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Learning and Retention Adaptations of Myoelectric Activity

During a Novel Multi-Joint Task

George D. V. Sarantinos

Department of Physical Education

McGill University, Montreal

Canada

May, 1999

A Thesis submitted to the Faculty of Graduate Studies and Research

In partial fulfillment of the requirements for the degree of

Master of Arts

0 George D. V. Sarantinos 1999

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TABLE OF CONTENTS

ACKNOWLEDGEMENTS ......................................................................... v

.......................................................................................... ABSTRACT vi . . ............................................................................................. RESUME VII

... ................................................................................ LIST OF FIGURES v i i ~

LIST OF TABLES ................................................................................... x

GLOSSARY OF DEFINITIONS AND ABBREVIATIONS ................................ .xi

CHAPTER I

INTRODUCTION ................................................................................ - 1

1 . 1 General Objective ........................................................................... 1

......................................................... 1.2 Nature and Scope of the Problem 3

................................................................. 1.3 Statement of the Problem -5

1.3.1 Assumptions and limitations ...................................................... 6

1.4 Hypotheses .................................................................................. -7

1.5 Rationale .................................................................................... -7

CHAPTER 11

METHODOLOGY ................................................................................ -9

................................................................................ 2.1 Participants -9

2.2 Apparatus ................................................................................. -10

2.3 Experimental Task and Protocol ........................................................ I0

2.4 Data Acquisition and Analysis .......................................................... 16

....................................................................... 2.5 Statistical Analysis -24

CHAPTER In

.......................................................................................... RESULTS 25

............................................................ 3.1 Participant Characteristics - 2 5

3.2 Adaptations in Performance Outcome with Learning and Retention ........... - 2 7

3.3 Adaptations in Performance Production during both Learning and Retenion .. -29

............................................. 3.3.1 Qualitative EMG Data Analysis 29

APPENDUC 7 ANOVA Table for the Performance Time Differences Between

the Experimental and Control Groups.. ................................. -123

APPENDIX 8 ANOVA Table for the Composite Score Data of W2 for the

.............................................. ...... Experimental Group.. .. -1 24

APPENDIX 9 ANOVA Table for the Composite Score Differences of W2

Between the Experimental and Control Groups.. ..................... .125

APPENDIX 10 Within Muscle Group Representations of W3 for the

Experimental Group - Day 1 to Day 5.. ................................ 127

APPENDUC 1 1 Within Muscle Group Representations of W3 for the

Experimental Group - Ret 1 to Ret 2.. ................................. -1 29

APPENDIX 12 Within Muscle Group Representations of W3 for the

Experimental Group - Ret 2 to Ret 3.. .................................. 13 1

APP ENDIX 1 3 Within Muscle Group Representations of W 3 for the

Experimental Group - Ret 3 to Ret 5 . .................................. 1 33

APPENDIX 14 Within Muscle Group Representations of W3 for the Control

Group - Day 1, Day 5 and Ret 5.. ....................................... 135

ACKNOWLEDGEMENTS

1 would like to express my appreciation for the support provided by my thesis

advisor Dr. René Turcotte, who encouraged me to persevere through the myriad of

challenges offered by the undertaking of this research.

1 also extend my thankfulness to the chairman of the Physicai Education

Department Dr. Greg Reid, for his assistance in the finalization of this project.

Special prayers are offered to Dr. Vassilios G. Vardaxis for his expertise and

association in this work and to his wife Panayiota and their chikiren George, Petros and

Theodore.

Extra admiration is held for the participants of this study without whom the

current investigation would not have been realized!

ABSTRACT

The learning and retention adaptations of muscle activity were studied during a

novel multi-joint task. Electrornyographic (EMG) signals were recorded fiom the

posterior deltoid, long and lateral heads of the triceps, pectoralis major, biceps and

brachioradialis muscles. These data were assayed in a pattern recognition analysis (SVD)

to ascertain the minimum number of 'common features7 or waveforms (W's) required to

describe the set of input EMG patterns (IP).

Fifteen participants perforrned targeted arm rnovements, which incorporated the

shoulder and elbow articulations, as fast and as accurately as possible in the horizontal

plane. Both experimental (E) and control (C) groups were employed. The E group was

trained (Day 1 to Day 4) and tested both pre- and post-learning. They were further re-

tested during a retention period (ET) consisting of 1, 2, 4, 6 and 8 week post-learning

sessions. The C group was tested before and after leaming and at the end of the RET

period.

The SVD analysis revealed three W's among the six IP7s. The first W(1)

represented a "running average" of the iP's with a generally higher load for the lateral

head of the triceps across both learning (LRN) and RET conditions. The second W(2)

demonstrated an 'out-of-phase' relationship that defined an increase in reciproca1

inhibition between the agonist (AG) and antagonist (ANT) muscle groups within each of

the shoulder and elbow joints with LRN. The third W(3) described the relationships

among the muscles within each of the AG and ANT groups. The AG group revealed an

enhanced proximal to distal activation of the muscles with LRN while the ANT group

exhibited a decreased representation and/or intensity of the muscles involved in the motor

task for the same period.

The adaptations in both the intensities of the out-of-phase relationship (W2) and

the proximal to dista1 activation of the AG group (W3) demonstrated a persistence of the

motor memory program consolidated with motor skill acquisition at one-week post-

learning. At two weeks post-learning, however, a decrement in the aforementioned

adaptations was revealed by each of W2 and W3. This demonstrated a motor memory

program that was indeed impressionable to an interruption in specific motor task training.

v i

Les adaptations de l'activité musculaire concernant l'apprentissage et le maintien

d'une habilité motrice ont été éxaminés dans cet étude a propos d'une tâche multi-

segmentaire. Les donneés électromyographiques (EMG) ont été enregistreés pour le

deltoïde postérieure, le grand pectorale, les portions longues et vaste externes du triceps.

le biceps et le brachioradiale. Ces enregistrements ont été analysés dans une méthode de

reconnaissance de motifs principaux, nécessaires à décrire la série des traces EMG.

Quinze participants ont éxécuté des movernents du bras à une cible, incorporant

les articulations de l'épaule et du coude, aussi rapidement que possible dans le plan

horizontale. Les membres d'une groupe expérimentale (E) et de contrôle (C) ont été

employés. Le groupe E a suivi un entraînement de quatre jours et a été évalué a chacune

des sessions avant et après l'apprentissage (APPR) ainsi qu'à 1, 2, 4. 6, et 8 semaines

apres I'APPR [les étapes de maintien (MAINT)]. Le groupe C a été évalué avant et apres

1' APPR ainsi qu'à la fin de la période de MAINT.

L'analyse a révélé trois traits communs (TC) parmi la série de traces EMG. Le

premier trait commun (TC1) consistait de la moyenne des traces EMG avec un

coefficient préférentiel pour la portion vaste externe du triceps a travers toutes les

conditions de I'APPR et de MAINT. Le deuxième trait commun (TC2) a demontré une

élévation de l'inhibition réciproque entre les muscles agonists (AG) et antagonistes

(ANT) à Ia suite de I'APPR. Le troisième trait commun (TC3) a décrit les relations panni

les muscles dans chacun des groupes AG et ANT, révélant une activation rehauseé du

séquence proximale au distal des AG et une décroissance du nombre et/ou de l'intensité

concernant l'activation des ANT.

Les adaptations demontrés par TC2 et TC3 ont révelé une persistance du

programme moteur en mémoire qui a été consolidé avec I'APPR jusqu'a une semaine

apres la fin de l'entrainment. Cependent, à deux semaines apres l'entrainement, les

adaptations de TC2 et TC3 ont subi des détériorations qui ont indiqués que le programme

moteur était susceptible à affaiblir suite à l'inactivité.

Figure 18. Sample singular value decomposition analysis on EMG patterns for

a single participant, four weeks pst - leamhg (Ret 3). ......................... .42

Figure 19. Sample singular value decomposition analysis on EMG pattems for

.......................... a single participant, six weeks post-learning (Ret 4). -43

Figure 20. Sample singular value decomposition analysis on EMG pattems for

...................... a single participant, eight weeks post-leaming (Ret 5). ..44

Figure 21. Eigenvalue fluctuations and prominent muscle characteristics for W 1

of the experimental group.. ....................................................... .46

Figure 22. Eigenvalue fluctuations and prominent muscle characteristics for W 1

................................................................ of the control group.. 48

Figure 23. Eigenvalue fluctuations and intensity of the 'out of phase' relationship

............................... as revealed by W2 for the experimental group.. .50

Figure 24. Eigenvalue fluctuations and intensity of the 'out of phase' relationship

as revealed by W2 for the control group.. .................................... ...52

TABLE 1. Anthropometric characteristics for the participants of the

experimental and control groups-. .............................................. . .26

TABLE 2. Eigenvectors of each of the waveforms W1, W2 and W3, for al1 levels

of leaniing and retention for the motor task of participant P7.. ................ 57

TABLE 3. Eigenvalues, percent variabi iity accounted for by each wave form

and the sum of al1 three W's within both learning and retention levels

................................. for the motor task of the experimental group.. ..6 1

TABLE 4. Eigenvalues, percent variability accounted for by each waveform

and the surn of d l three W's across post-training and post-retention

periods of the control group.. ....................................................... 63

GLOSSARY OF DEFINITIONS AND ABBREVIATIONS

Basis Functions (BF's): Basis functions are also referred to as "common features" or

waveforms (W's) that are representative of the original input pattems to a singular

value decomposition algorithm.

Bic: Short head of biceps brachii.

BrR: Brachioradialis.

Composite Score: The difference between the highest and the Iowest points on an

eigenvector (W2) which provides an indication of the degree of latency between the

agonists and antagonists under investigation.

Coordination: Collectives of muscles and joints that are involved in the control of a

speci fic action (Bernstein, 1967).

EMG: Electromyogram.

Cross Motor Skiil: An action or task that is charactenzed by the utilization of large

musculature and smooth coordination of movement where the precision of

movement is not as important to its execution as it is for a fine motor ski11 (Magill.

1993).

LA: Lateral head of the triceps brachii.

LO: Long head of the triceps brachii.

Pec: Pectoralis major.

PD: Posterior deltoideus.

PT: Performance time.

Ret: Retention condition.

SVD: Singular value decomposition analysis that involves a reformulation of a set of

input patterns into a smaller set of basis functions which are derived fiorn the

original data. It was employed herein to evaluate the eigenvectors and eigenvaiues of

the input EMG pattems.

Whipping Movement: A movement that involves the rotation of al1 joints in a similar

direction.

INTRODUCTION

1.1 Gen eral Objective

Motor behavior is an integral part of our daily lives. Many of o w movement

capabilities are enacted to realize particular movement objectives within various

movement contexts, including walking, running, throwing, kicking, etc. These skills have

been acquired throughout our motor development by active practice. They have been

learned both as practical skills and through participation in recreational and/or sporting

endeavors.

Motor skill learning entails the selection and timing of many muscles across

multiple joints and thus the coordination of those joints (Brooks, 1986). An interesting

phenornenon of inquiry would not only concem the nature of motor skill acquisition but

also, and eq uall y as signi ficant, the consequences of terrninating or abstaining fiom

movement practice. In other words, would the acquisition of multi-joint coordination also

possess with it some element of "use it or lose it"? Just how resistant would complex

motor ski11 learning be to forgetting?

Bernstein's (1967) theory of motor coordination relates the problern of the

multitude of degrees of freedom encountered by the leamer in the acquisition of a new

motor skill. Specifically, the minimization of those degrees of fkeedom and the

development of efficient movement are what characterize motor coordination. It is the

purpose of this study to inquire into the reduction of degrees of freedom with leaming

and investigate the consequences of terminating movement practice on multi-joint

coordination.

Compound (rnulti-articular) limb movements, that are learned and adapted to a

particular activity or sport, reside within the central nervous system [CNS (i.e. brain and

spinal cord)] in the form of overall plans, narnely complex motor prograrns (Brooks,

1986). The neuromuscular transmission of these motor behaviors is mediated by the

motor unit, the final common pathway of neuromotor k c t i o n (Brooks, 1986).

Ultimately, both centrally and peripherall y processed commands are translated into force

by the effector organ, skeletal muscle (Vandervoort, 1 WZ), enabling the muscles

involved in a motor action to operate in a smooth and expedient manner. A decrement in

the motor performance of a previously acquired complex skiII, (due to the tennination of

practice or training), would be difficult to measure if changes first manifested themselves

at the neuromuscular level. Consequently, inquiries regarding the acquisition and

subsequent retention of multi-joint movement patterns would necessitate a

comprehensive analysis of neuromuscular function; that is, an analysis of performance

production rneasures (Magill, 1993).

Motor skill learning research has often utilized electromyography (EMG). as a

performance production measure, to study the neural activation of human skeletal muscle

within the context of single (Persons, 1958; Finley, Wirta and Cody, 1968: Payton and

Kelley, 1972) and multi-joint coordination (Normand, Rouillard and Tremblay, 1982;

Hasan and Karst, 1989; Karst and Hasan, 1991). The intermuscular latencies and

amplitude of EMG activity in the agonist and/or antagonist muscles under investigation

have been used to infer specific modifications in neuromuscular coordination consequent

to learning (Kamon and Gormley, 1968; Hobart, Kelley and Bradley, 1975; Vorro and

Hobart, 1981; Engelhom, 1983). Indeed, EMG measures are considered to be the

"gateway" or "window" to the various motor programs within the CNS of the individual

(Ange1 and Garland, 1971; Angel, 1975; Strick and Waters, 198 1 ; Jemings and Sanes.

1984).

Earlier work by Persons (1958), for instance, reported a reciprocal activation of

agonist/antagonist involvement in the development of a motor habit, which supplanted a

previously unorganized pattern of simultaneous activation concerning opposing muscles.

Later, in a pilot study, Payton and Kelley (1972) observed what appeared to be a

differentiation of two muscles involved in a motor skill, into both auxiliary (supporti~te)

and prime mover roles; and that the reduction in total muscle activation and duration of

the movement agonist responsible for the successful performance of the motor task

indicated a more efficient use of that muscle.

Vorro and Hobart (1981) who extended the work of Hobart et al. (1975). using a

unilateral ball tossing task, confirmed that with practice an increase in the total electricat

output of a rnovement agonist served to increase limb velocity at ball release while an

increase in the activity of the antagonist functioned to decelerate the limb, producing a

braking e ffect. The latency of both muscles had also decreased substantiall y following

practice underscoring as Ludwig (1982) himself has suggested, the importance of

intemuscular timing in motor ski11 learning.

A detailed electromyographical analysis of the retention aspects of a newly

acquired complex motor ski11 is still not entirely evident in the literature. Within the

context of the present study, the EMG changes in the agonist and antagonist muscles of a

previously l emed bi-articular motor task will be measured to assess the persistence of

neurornuscular multi-joint coordination.

1.2 Nature and Scope of the Problem

In motor learning research, the concept of 'motor memory' is used to underscore

the importance of a person's sense of effort and its memory in both the planning and

execution of motor action (Brooks, 1986). Specifically, motor prograrnrning functions as

an indelible neuromuscular foundation that is set in the progressive, systematic

performance of any motor act. What remains to be clarified, entails the characterization of

the tenability of the resultant motor schema as a fùnction of motor skill leaming.

in even the simplest motor behavior, mediated by the vertebrate CNS, the spinal

stretch reflex (SSR), or tendon jerk in the biceps or triceps brachii, has shown an adaptil-e

plasticity in primates wherein SSR amplitude can be changed without modifications in

initial muscle length or background EMG activity (Wolpaw, 1983; Wolpaw et al., 1983;

Wolpaw et al., 1986; Wolpaw, 1994).

Following a 60 day control mode, whereby the initial amplitudes of EMG activity

(in volts) were determined in the primates, Wolpaw et al. (1986) proceeded to either

increase (SSR-up mode) or decrease (SSR-dom mode) the magnitude of the response via

operant conditioning (for 35-274 days) of the SSR pathway [Le. the Ia afferent fiber from

the muscle spindle, its synapse on the alpha-motor neuron and the alpha-motor neuron

itself (Wolpaw, l986)J.

Specifically, a two phase learning process of both experimental modes was

identified, composed of an early precipitous, although small, modification in EMG

response followed by a more gradual, incremental change that ultimately accounted for

80-90% of the final change. Furthemore, the average SSR amplitude in the control mode

as well as in the SSR-down mode were shown to persist during a senes of gaps in

performance of 10-38 days suggesting a persistent aiteration at the segmentai level. An

increase in SSR amplitude as a result of training was found to decay slowly over weeks,

however. with a half-life of about 17 days.

Motor learning paradigms of simple, single-joint, voluntary Iimb movements have

consistently demonstrated a characteristic decrease in task error variance d u h g practice

leading to improved motor performance (Persons, 1958; Payton and Kelley, 1972;

Hobart, Kelley and Bradley, 1975; Hobart, Vorro and Dotson, 1978; Vorro and Hobart,

1981; Ludwig, 1982; Engelhorn, 1983; Corcos et al., 1993; Vardaxis, 1996). This

improvement, which according to Newell (1991) "is due to the acquisition of

prescriptions for action that speciS the movement dynamics in relation to the task

demands" also follows a curvilinear fhction in which rnovement stability is realized

early on in motor practice (Corcos et al., 1993; Vardaxis, 1996).

Information regarding the underlying myoelectric activity patterns comrnensurate

with enhanced performance due to motor training, however, has been equivocal in view

of the task and procedure specific nature of the separate investigations (Persons, 1958;

Payton and Kelley, 1972; Vorro and Hobart, 198 1 ; Engelhorn, 1983).

Motor ski11 practice has exhibited an increase, decrease, or no change in the

amplitude and/or duration of EMG activity in opposing muscles kom pre-learning to

post-learning trials (Payton and Kelley, 1972; Finley, Wirta and Codey, 1968; Payton,

Sue and Meydrech, 1976; Jeagers, 1989). More important, however, have been the

modifications in intennuscular latencies and electromechanical characteristics associated

with ski11 acquisition (Person, 1958; Hobart et al., 1975; Hobart, Vorro and Dotson, 1978;

Vorro and Hobart, 198 1 ; Ludwig, 1982; Engelhom, 1983; Corcos et al., 1993; Vardaxis,

4

1996). Additionally, there has also been evidence conceming the use of mental practice

along with physical practice to increase the rate of motor skill learning (Maring, 1990).

Until recently, the study of the enhanced performance of single- or rnulti-degree

of fieedom movement due to practice has provided data inferring the effects of abstention

fiom motor training on ski11 acquisition. Using such performance production measures as:

(a) angular or linear displacement, velocity and acceleration (kinematics), (b) forces,

torques and powers (kinetics) and (c) muscle activation patterns (electromyography) in

their analyses, researchers observed improvements in motor behavior during one

experirnental session that were partially retained and demonstrated at the start of the next

session (Corcos et al., 1993; Vardaxis, 1996).

Now, CO-extensive with investigations into motor learning are demonstrations of

motor skill retention, including the lasting temporal characteristics of intemal mode1 (IM)

consolidations of the dynarnics of an acquired motor task (Shadmer and Brashers-hg.

1996; Shadrner and Holcomb, 1997).

Furthemore, researchers' tests of critical time periods following practice reveal

an ongoing development of such M ' s from fragile to more stable representations in

motor rnemory (Shadrner and Holcomb, 1997; Brashers-Krug et al., 1996). There is also

evidence of the dynamic neural mapping associated with motor skill Iearning and

retention using functional magnetic resonance imaging (MN) and positron emission

tomography (PET) (Kami et al., 1995; Shadmer and Holcomb, 1996).

The present study investigated the adaptations in neuromuscuiar coordination

consequent to both learning and retention using electromyography to further the scope of

Bernstein's problem. If the CNS adopts strategies a d o r plans to minimize the number of

degrees of freedorn available to the learner mastenng a motor skill, then what would the

rarnmi fications to motor coordination be if movement practice were terminated?

A pattern recognition analysis of singular value decomposition (SVD) was used to

ascertain the minimum number of "common features" or waveforms required to describe

a set of six myoelectric signals of the left upper limb. This type of analysis will permit the 5

evaluation of the muscle activation patterns in their entirety and will entai1 the

interpretation of the temporal characteristics andlor the phasic information of the latter

whic h are O ften overlooked in discrete time-characteristic analyses.

1.3.1 Assumptions and Limitations

The limitations associated with the collection of surface electromyographic signais

include:

1. "Cross-talk" artifacts fiom adjacent muscles. in the present study, carefûl

exarnination for the detection sites was effected as well as outlining the same

locations for use across experimental sessions in order to minimize such artifacts.

7 . S kidelectrode irnpedance. Electrodekkin interface impedance was minimized

with thorough cleansing procedures involving shaving and mild abrasion of the

selected recording sites followed by alcohol swabbing.

3. Signal contamination consisting of prevailing noise from power line hum and

movement artifacts. Appropriate filtering and processing techniques were used to

control such influences.

Assumptions asociated with the experimental design and the motor task.

1. The EMG data will be asssumed to provide a measure of neurornuscular function

and a 'window' to the motor learning program(s) of the motor task.

3 -. It was assumed that the EMG data collected throughout the learning and retention

conditions of the experimental period represent the resulting adaptations of each

participant at the given interval as a function of the level of practice experienced

up to that period.

3. Each trial was assumed to have been accomplished as quickly as possible,

according to the outlined accuracy requirements of the motor task.

Hypoth eses

The SVD analysis will provide more than one significant waveform that will be used

to explain the six input muscle activation patterns of the experimental group across

both learning and retention conditions.

The waveform analysis will reveal more than a simple amplitude modulation of

muscle activity patterns within both learning and retention levels. It will characterize

the phasic adaptations between the agonist and antagonist muscle groups to define a

degree of reciprocal inhibition within the joints involved in the rnotor task.

The waveform andysis will characterize the phasic adaptations among the musctes

within each of the agonist and antagonist groups fiom pre- to post-learning

conditions. It wilI outline an increase in the proximal to distal relationship of the

agonists as well as an increased synergistic activation of the antagonists with

learning.

The waveform analysis will characterize the phasic adaptations between the agonist

and antagonist muscle groups to define a decrease in the reciprocal inhibition within

the joints involved in the motor task with a termination in training.

The waveform analysis will characterize the phasic adaptations among the muscles

wititin each of the agonist and antagonist groups after training has stopped. It will

demontsrate a diminution in the power of the proximal to distal pattern of the

agonists as well as a decrease in the synergistic activation of the antagonists.

Rationale

The study of multi-joint rnovement is warranted on the basis that many of our

everyday rnotor activities, recreational and sporting preserves, involve the coordination of

various muscles across many joints. Our actions are inherently complex, including the

arrangement of serial single-joint movements in the production of motor skills. The

investigation of singular muscles or joints, although informative, is not entirely practical.

Furthemore, the fact that motor ski11 learning occurs is an attestation to the

possibility that "what c m be gained may also be lost". Consequently, it was the focus of

7

the present research to inquire into the retention phenomenon as it applied to the

production of a complex rnotor task. In order to study motor ski11 retention, the issue of

learning must first be addressed; the function of which would be to establish a

comparative baseline performance level for the subsequent analysis of post-learning

adaptations. In this study, an experimental paradigm was employed to facilitate the

acquisition of a fast complex whipping movement. The neuromuscular correlates of

motor memory (i.e. the motor prograrns) were indirectly assayed via the

eIectromyographic activity of the various muscles subserving the movement to provide a

'gateway' into the underlying processes of the CNS.

The effects of an interruption or cessation in motor ski11 training have received

substantial attention among researchers in a variety of disciplines. These studies have

included explorations in pursuit rotor and tracking tasks of experimental psychology

(Bell, 1 950; Jahnke, 1 958; Hammerton, 1 963), strength training/detraining paradigms in

exercise physiology (Hakkinen and Komi, 1983; Hakkinen et aI., f 985) and

reachinglpointing movements of motor control (Shadmehr and Brashers-Kmg, 1 996).

However, there has been a limited focus, if any, on the retention of 'maximum effort'

type movements of curvilinear trajectories that are inherent in many complex athletic

skills such as throwing, kicking and striking with and/or without an implement. Although

these skills possess significant force distribution characteristics. they are also defined by

salient timing features of segmenta1 rotations which allow the practitioner of a motor ski11

to perform in an efficient manner that is distinguished by an absence of superfluous

actions-

The impressionability of the aforementioned timing features to imposed no-

training intervafs, is very important if the goal is to maintain a certain level of task

proficiency or to return to a previously acquired level of performance. Knowledge of the

time course of pertinent pauses in training would permit an informed decision on the

restructuring and implementation of training programs to realize resumption in a prior

motor leaming status.

CHAPTER II

METHODOLOGY

Each of the experimental sessions, including measurement of anthropometric data,

task proficiency testing and re-testing following the non-performance penods took place

in the exercise physiology laboratory of McGill University's Seagram Spon Science

Centre. The methods and procedures of this study will be delineated within the ensuing

sections: (2.1) Participants; (2.2) Apparatus; (2.3) Expenmental task and protocol; (2.1)

Data acquisition and analysis; and (2.5) Statistical analysis.

In this study, fifteen male volunteen between the ages of 18 and 30 years, with no

history of neurological or physical disabilities, were randomly assigned to either an

experimental (10) or control (5) group. Each person's age. height and body mass were

recorded for descriptive purposes.

A pre-requisite met by al1 participants was the determination of their right

arm/hand preference in normal daily as well as sporting activities, the function of which

was simply to provide each individual the goal of having to perform and subsequently

l e m a unilateral bi-segmental motor task with the non-preferred arm (i-e. the Iefi). For

this purpose a questionnaire (Appendix 2) was submitted to each prospective subject to

better establish strongly lateralized (Le. right-handers) individuals and ovemile

participant "ambidexterity".

A description of the expenmental task and protocol (Appendix 3) was provided to

each prospective participant before an infonned consent form was read, understood and

signed by the participants pnor to the start of the study (Appendix 4). Finally, a statement

of ethics approval was received prior to the start of subject data collection (Appendix 5 ) .

2.2 Apparatus

All training and testing of the study's participants occurred via a specially

designed experimental table. Each individuaI was seated in a straight-backed, armless

chair with the trunk of the body secured to the back of the chair using velcro straps so as

to minimize any extraneous movement of the shoulder joint. The chair was located on the

same floor space for each person and was adjustable, allowing each subject to be in the

same relative position when performing the required skill. More specifically, the surface

of the table met the torso of the individual below the axilla and allowed resting of the

subject's upper limb on it in between the trials and blocks of practice, see Figure 1A.

A plastic splint, extending the length of the forearm and pronated hand and

terminating distally (beyond the fingerç) in a circular lOcm - diameter plate, was h l y

secured to both the forearm and the hand via velcro straps. This procedure immobilized

the wrist, restricted movement to the elbow and shoulder joints only, and defined the

circular plate as the end-point target of the upper extremity.

Two photodiodes were affixed to the experimental table designating the starting

and stopping points of the task and will otherwise be referred to herein as the "home" and

"target" areas respectively. Each photodiode consisted of an emitter and a receiver which

established a narrow uniform beam when set, and depending on which beam was

intempted, the output of the photodiodes consisted of either O or 5 volts. A chronometer

to which the photodiodes were wired provided a ruming time count of the limb's

excursion fiom the "home" to the "target" positions.

2.3 Experimental Task and Protocol

Originated by Vardaxis (1996), the motor task that was performed consisted of a

two-joint "a11-out" unidirectional whipping movernent of the lefl arm involving

horizontal abduction at the shoulder and extension of the elbow, both occuning in the

transverse plane. The task was chosen on the b a i s of it being a novel, gross motor skill;

although not too difficult to perform, it required practice to master. Moreover, the task

was neither akin to any normal everyday movement nor to a specific sporting activity or

10

Figure 1 : A schematic representation of the experimental set-up. (A) side view (B) top view.

skill. It did possess similar characteristics to such movements as striking and kicking with

the limbs and/or with implements, for instance, in that both c m be executed with relative

maximum effort, and to an extemal target. However, these movements would involve

different muscle groups, alternative planes and ranges of motion as well as contact with

objects as targets.

To begin with, a 'ready' or 'still' position was defined with the subject fitted to

both the chair and forearmhand splint, his arm in 90 degrees of shoulder flexion and 90

degrees of elbow flexion, with the circular end-point plate intersecting the beam of the

"home" photodiode. The subject was instmcted to move his hand fiom the "home" to the

"target" photodiode position, which could only be accomplished by a 45 degree

horizontal shoulder abduction and 180 degree elbow extension, as quickly as possible, see

Figure 1 B. The two photodiodes were adjusted to accommodate the variable segmental

lengths of each of the participants and ensure the same angular displacement for the two

joints during task execution.

The movement did not consist of a reaction time task. Prior to each trial the

experimenter prepared each subject with the phrase "Whenever you are ready ...".

whereupon the latter moved his am, to accomplish the task, on his own initiative and

without undue hesitation. A 'final' position was defined by the end-point plates' complete

stop at and intersection of the "target" photodiode beam.

With the arm segments (Le. brachiurn and fore-) operating in the horizontal

plane and rotating around the longitudinal axes of each of the glenohumeral and elbow

articulations, the following single and double joint agonist muscles were assayed: the

posterior deltoideus (single-joint horizontal shoulder abductor) and the long and Iateral

heads of the triceps brachii (double-joint horizontal shoulder abductor/elbow extensor and

single-joint, elbow extensor respectively).

The single and double-joint antagonist rnuscies consisted of: the clavicular

pectoralis major (single-joint, horizontal shoulder adductor), short head of the biceps

brachii (double-joint, horizontal shoulder adductor and elbow flexor), and brachioradiafis

(single-joint, elbow flexor).

Since motor skill learning has been demonstrated to occur even after many

hundreds of repetitions (Nomand et al., 1981; Gottlieb et al., 1988; Corcos et al., 1993)

the protocol selected was similar to that used by Vardaxis, (1996) which was shown to

facilitate complex motor skill acquisition. The experimental group performed three (3)

sets of twenty-five (25) trials, for a total of seventy-five (75) trials per day on four (4)

consecutive days. There was a 24 h o u period between testing sessions and each session

was undertaken at the same time of day for each individual to minimize any diurnal

change in performance (Corcos et al.. 1993).

Each set was intempted by a 5-min. rest period in an effort to minimize fatigue.

They were also allowed to rest between trials whilst receiving performance feedback

from the experimenter. The specific feedback was verbal, relating to both the movement

time and accuracy demands of the task as observed by the experimenter on a cornputer

monitor at the end of each trial. Performance time (PT) consisted of the elapsed time

behveen the circular end-point plate's departure from the "home" position (movement

onset) to its arriva1 at the "target" point (movement end). The accuracy demands of a

successful trial entailed the single intersection of each of the "home" and "target"

photodiode beams by the circular end-plate, see Figures 1 B and Figure 5.

Eac h individual of the experimental group was accorded ten (1 0) familiarization

trials without feedback on the first testing day. This process acquainted him with the

procedures of the task as well as with the experimental apparatus; these trials were

discarded at the time of the analysis. Subsequently, ten (10) preparatory, or "wm-up".

trials without feedback were permitted prior to the actual practice trials of the first and at

the beginning of each of the remaining practice sessions on succeeding days.

In addition to being used to prepare the individual for an optimal level of

performance, the latter five of the ten wann-up trials for each of the four practice sessions

constituted the learned trials or the 'stable' adaptations of the task (Le. the aspects of the

motor task which had been retained). Evidently, on the first day of practice, these five

stable adaptation trials consisted of an initial performance level in the motor task. The last

five of the practice trials of each of the aforementioned training days comprised transient

learning, which featured the level of task proficiency attained as a result of training for

that particular day.

Also included was a fif3.h day incorporating ten (10) successful trials of which the

latter five trials were used to determine the final stable adaptations of the motor task or

the resultant leaming level as a function of the four-day training protocol. Only the two

sets of five stable adaptation trials f?om Day 1 and Day 5 fiom each individual were used

in the ensuing analysis, to determine the learned aspects of the rnotor task. Transient

learning will not be addressed in this study. A complete representation of the

experimental protoc01 is offered in Figure 2.

It should be noted, however, that the greater the number of testing trials required

before actual practice in the task, the greater the conceivable index or gauge of learning

which can be procured fiom the ensuing training mals (Corcos et al., 1993). The risk that

is run, though, is one that exacts fûrther pressure on the patience of the subjects

cornmitted to the study, who may already be performing to the limits of their discretion.

Consequently, the nurnber of warm-up trials used in this study was determined according

to the above contention as well as in view of the familiarization and pre-training

procedures used by Vardaxis, ( 1996).

Motor skill learning or task proficiency was determined by the following

performance outcome criterion: a decrease in the performance time of each person. to

within a stabilized time period. Following the training protocol, there was a 'time-course'

method used to evaluate the effects of 'no-training' or 'no-practice', consisting of

increasing retention intervals. It was systematized in a manner that required the

expenmental group to abstain fiom the task for an initial one week period (starting fiom

the end of Day 5 to the following seventh day - Ret 1) at the end of which al1 returned for

a re-testing session of 10 successfûl trials. Once again, the first five attempts constituted

warm-up trials while the latter five stable adaptation trials were used in the analysis. The

participants desisted tiom practicing the task for another week followed by the same re-

testing protocol at this, the second week post-learning (Ret 2). They underwent a similar

re-testing procedure at 4, 6 and 8 weeks post-leaming (Ret 3, Ret 4 and Ret 5

respectively). Only trials 6-10 of each of the five retention intervals (i.e. the 5 stable

14

[I F A M I L I A R I Z A T T PRA CTICE I TRANSIENT 1

II Trials: 1

5 1 5 Il

Figure 2: The experimental protocol for leaming of the motor task. The farniliarization, preparation and stable adaptation trials did not include feedback. Stable learning represents the adaptations consolidated in memory. Transient learning which included feedback reflects the practice effect within experimental sessions. Transient learning was not assessed in this study.

15

adaptation trials at 1, 2, 4, 6 and 8 weeks post-leaming) were analyzed. These p ~ i c u l a r

time penods were chosen to represent two short-term (Ret 1 and Ret 2), and three long-

t e m (Ret 3, Ret 4 and Ret 5) 'non-performance' possibilities, in order. An overview of

the retention protocol is available in Figure 3.

The control group performed 10 familiarization trials without feedback followed

by 10 additional 'successful' trials on the fint day o f the learning period of which the

latter 5 of the 'correct' trials were analyzed. As well, each control subject performed 10

successhil tnals of the task on the fifth day of the learning penod and at the completion of

the expenment; on the day of the fifth retention interval. see Figure 4. Only the latter 5

tnals of each of the three conditions were subjected to the ensuing analysis.

Al1 subjects were requested to abstain from either performing the experimental

task privately (Le. on their own) or engaging in any progressive resistance type training of

the upper limbs and trunk during the entire experimental period. Furthemore. they were

asked to keep a log of their physical activities and sports participation (recreational or

othewise) during each of the retention periods for the expenmenter's information.

2.4 Data Acquisition and Analysis

During the experimental penod the electrical output of the muscles under

investigation was recorded using disposable, uni-patch dual-element silver/silver chloride

surface EMG electrodes. These bi-polar electrodes were placed near the enervation points

and onented longitudinally according to the muscle fiber direction of each of the six

muscles (Warfel, 1993; Kearney, 1994). In order to ensure the same electrode placement

for al1 seven testing sessions (Le. Day 1, Day 5 and Ret's 1 - 5 ) , the specific sites were

marked with a non-toxic permanent ink marker. A ground electrode was located on the

stemal extremity of the nght clavicle.

To minimize electrode impedance and decrease the skin potentials at the

elec trode/skin interface sites, the surface areas used to monitor muscle activi ty were

shaven of epidermal hair, abraded of dead skin cells and cleansed by alcohol swabbing

(Kearney, 1994). Care was also taken regarding electrode placement to avoid the

PROTOCOL WTFJVTION)

P R E ~

1 PREPARA TION

Trials: 5

PREPARA TION Trials: 5

II Trials: 5 II

5

STABLE 5

11 P R E P A R A T ' N 1 STABLE 1 11 Trials:

L

5 I 5 II

Figure 3: The experimental protocol for retention of the motor task. The preparation and stable adaptation trials did not include feedback. Stable learning represents the adaptations consolidated in mernory.

PREPARA TION STABLE Trials: 5 5

c

F A M ~ ~ STABLE I>

PREPAM TION STABLE Trials: 5

Trials: 15

Figure 4: The control protocol including matching intervals for Day 1 (before learning), Day 5 (after learning) and Ret 5 (8 weeks post-learning).

5

potential of "cross-talk" or interference in the signal of one muscle from adjacent muscles

(Kearney, 1994).

Al1 six 'raw' EMG signals were recorded via an eight channel GRASS High

Performance AC Preamplifier (mode1 p5 1 I ). Powered by a regulated power supply it

included a 60 Hz notch filter, 20 Megaohm input impedance amplifiers. 4 microvolt

sensitivity and a Cornmon Mode Rejection Ratio (CMRR) adjustable to 10 000:l at 60

Hz. Individual signals were differentially arnplified with a gain of 1000, and band-pass

filtered with the high and low cut-off fiequencies set at 10 and 1000 Hz respectively.

The EMG data along witb the two photodiode signals were then passed through

eight, gain and phase-matched, pole Bessel analog low-pass active anti-aliasing filters

with a cut-off frequency of 250 Hz (Frequency Devices). The conditioned signals were

digitized at a sampling rate of 1000 Hz by an analog to digital board. They were

represented as both raw and full-wave rectified EMG waveforms on a computer analog

display using Labview: a prograrn development application that uses graphical

programming language, (G), to make programs in block diagram form. The program. or

virtual instrument (VI), that was accessed employed a conditional retrieval mechanisrn to

speciQ a software trigger, which started the acquisition and made the data availabie while

the VI continued to operate. By design, a11 six of the muscle activation waveforms fiom

each trial, including both photodiode signals, were observed in a two second acquisition

-window' including a 500 ms pre-trigger time, prior to being saved on computer

diskettes, see Figure 5 .

Further analysis of the stored EMG records entailed the smoothing of individual

EMG patterns using a fourth order Butterworth low-pass digital filter applied in both

directions to avoid any phase shift (Vardaxis, 1996). Additionally, the EMG data were

normalized for performance time (PT) in such a way as to include an 80% PT period

before movement onset as well as a 20% PT period afler the temination of the

movernent.

The time base of each resulting EMG trace was then resarnpled in MATLAB, a

rnatrix laboratory computer software prograrn (version 4.0), to 100 points in total, taking

I I 4 - 2 - PECTORALIS MAJOR

O * * -

f I

s 1 - I I E -

0.5 - Y *-

LONG HEAD OF TRICEPS > A -- O

4 - > 2 - w

.- Y

2 I

C3 1 - 0.5 -

W BICEPS

1 * LATERAL HEAD OF TRICEPS

O I

- START

0.5 1 .O 1.5

Time (sec)

i 1

1 HOME PHOTODIODE I f

O 5

Figure 5. A typical dataset as acquired for a single trial of the motor task including: ( 1 ) event triggers (Home and Target) and (2) the muscle activation patterns cf the PD, Pec, LO, Bic, LA and BrR.

I I

CT) 1 I END

TARGET PHOTODIODE

.- al 4 : t=

2

1 I

I I

- 1 I

O - I

into account both of the pre- and post-performance time provisions resulting in a data set

consisting of:

Motor task = 80% PT +- PT + 20% PT

100 points = 40 pts. + 50 pts. + 10 pts.

(Vardaxis, 1996). The resarnpling procedure did not change the nature of the individual

EMG traces, rather, it enabled the temporal evaluation of al1 the EMG pattems on an

equal time line. Every processed signal was also nomalized to peak ( 1 00%) amplitude,

see Figure 6. Further processing of the stored EMG records entailed averaging the five

trials for each of the six different muscles, fiorn each of the learning (Day 1 and Day 5)

and retention (Ret's 1, 2, 3, 4 and 5) levels, for each subject of the experimental group.

The five trials fiom each of the three testing sessions of the control group. as deheated

above, were prepared in a manner consistent with that of the expenmental group.

The averaged and smoothed data that were performance time nomalized were

then quantitatively assessed using Singular Value Decomposition ( S m ) analysis, also

known as Principal Component (PC) analysis. SVD is a mathematical technique that can

facilitate the quantification of specific component contributions to myoelectric patterns.

among other electrophysiological phenornena (Flanders, 199 1 ). Specifically. the analysis

involves a reformulation of a set of input patterns into a smaller set of basis functions

(BF's) which are derived fiom the original data. In this manner, the patterns of different

experimental conditions c m be compared or contrasted.

Each bais fùnction, also referred to as a "common feature" or simply a waveform

(W). is orthogonal in relation to other BF's in that the dot product or covariance of any

two W's is equivalent to zero. The W's of the SVD analysis are not sinusoidal however;

insteâd this analysis is more like Fourier analysis since each of the original input patterns

c m be reconstnicted as a weighted sum of the W's. The construction of an auto-

correlation matrix enabled the calculation of the W's. The eigenvectors of the

syrnmetncal matrix consisted of the W's among the input patterns while the eigenvalues

signified the energy contained in each of the waveforms. Consequently, a waveform will

be descnbed herein as a signal that is representative of al1 of the input pattems analyzed,

which possesses a rneasure of variance accounted for by (Le. the eigenvalue). If, then, al1

2 1

of the waveforms are used with respect to an equal number of input pattems, al1 of the

variance cm be accounted for (Le. 100%).

The aim of the SVD analysis was to determine the minimum number of

waveforms required to describe the EMG data for each of the leaniing and retention

conditions of the experiment. That is, how the eigenvalues and eigenvecton of the

analysis changed with learning and, more importantly, following periods O f abstinence

fiom motor task training. An evaluation of the complete myoelectric signais focussed on

the phasic characteristics of the data to elucidate the temporal patterns of muscle

activation.

Numerous researchers have employed singular value decomposition analysis, also

known as principle component analysis, as a technique to quantify the pattems of muscle

activation associated with movements of the upper and lower extremities (Patla, 1985;

Soechting and Lacquanity, 1989; Flanders, 199 1 ; Flanders and Hermann, 1992).

Furthemore, investigators have recently used SVD in the evaluation of movement

synergies employing kinematic data in hurnan locomotion (Mah et al., 1994). the anaiysis

of cerebral activity fiom a multi-channel electroencephalograrn (Lagerlund. Sharbrough

and Busacker, 1997), and in the extraction of repeating pattems in cyclic biomechanical

data (Stokes, Lanshamrner and Thorstensson, 1999).

The singular value decomposition analysis was executed using the SVD algorithm

contained in MATLAB (version 4.0). The analysis was initially performed for each of the

learning levels in this study, using the myoelectric patterns of the six different muscles,

for each participant of the experimental group. That is, a set of six input pattems from

each of Days 1 and 5 per individual. tt should be noted that each EMG trace represented

an average of the corresponding five trials for each of the two learning levels that was

normalized to both percent performance time (100%) and peak amplitude (lOOOh), (see

Figure 6). The analysis was used to determine any changes due to learning after the shape

of the waveforms, the eigenvalues and eigenvectors were evaluated.

SVD was also performed for each of the five (5) post-trainingketention levels by.

once again, using the six different muscle input pattems for every subject of the

experimental group. In this manner, any changes within the 'non-performance' intervals

22

100 -

1 O0

40 Pectoralis Major 20

O

80 60 40 20

100

Percent Performance Time

- - Posterior Deltoid - -

80 60 40 20

Figure 6. Sample averaged and smoothed EMG waveforms for al1 six muscles that have been normalized to both penormance time (100%) and peak ampiinide (1 00%) before input to the singuiar value decomposition analysis.

O =

- - - Lateral Head of Triceps -

O

would be demonstrated. Fwtherrnore, cornparisons between the analyses of both the

learning and retention levels conceming the changes in the activation patterns of al1 the

muscles at once was also possible; specificaliy in terms of the timing characteristics of

the myoelectric signals.

Equally, SVD was employed on the EMG signals of the six muscles of each of the

subjects of the control group on the first and f i fth days of the learning period as well as on

the day of the fifth retention period.

2.5 Statistical A nakysis

A two-way repeated measures univariate analysis of variance (ANOVA) was used

to compare the expenmental and control groups, at three points in time of the expenmetal

period: (1 ) the first day of practice, Day 1, (2) the final day of testing in the fearning

protocol, Day 5, and (3) on day of the final retention interval, RET 5. The single

dependent variable that was analyzed included the performance outcome measure of

performance time.

Additionally, a repeated measures one-way analysis of variance was conducted on

the experimental group to identiw any changes across the five levels of practice or

training and five retention intervals using, once again, performance time as the dependent

\ x i able.

SVD analysis will be presented qualitatively in this study.

RESULTS

The present study investigated the neuromuscular adaptations consequent to both

Ieaming and retention conditions of a novel muhi-joint task. The linear envelope detected

EMG profiles (waveforrns) were used in an SVD analysis, as an indirect measure of

neuro-motor function, which aIluded to the motor prograrns of the C N S . The aim was to

elucidate the changes occurring with motor task practice and more specifically, to

determine the effects of abstaining fiom such exercise. A time course evaluation of motor

ski11 retention was employed to test the stability of the resultant motor coordination as a

function of motor ski11 leaming. The topics conceming this chapter wiIl be subdivided

into the following sections: (3.1) Participant characteristics, (3.2) Adaptations in

performance outcome with learning and retention and (3.3) Adaptations in performance

production during both learning and retention.

3. I Participant Characteristics

Fi fteen male volunteers agreed to participate in the present study, without

remuneration, following an explanation of the experimentai task and protocol and the

signing of an informed consent form. Ten individuals were randomly assigned to an

expenmental group while five others were likewise allocated to a control group. They

reported no persona1 injuries or prior history of neurological, motor system, disorders. All

participants identified themselves as right arm preferred for the motor tasks listed within

the questionnaire. Their ages ranged from 23 to 34 years, with a mean age of 26.6 years.

The heights and body masses of the participants ranged fiom 1.65 to 1.85 m and 67.3 to

106.8 kgs respectively. Table 1A displays the age, height and body mass for each

participant of the experimental group. Table 1B shows the same data for the members of

the control group.

TABLE 1

A. An thropometric charactenstics for the participants of the experimental group.

Participant Age (Years) Heigbt (m) Body Mass (kg)

Mean (* SD) 26.6 (* 2.91) 1.76 (* 0.07) 76.7 (& 12.00)

B. Anthropometric characteristics for the participants of the control group.

Participant Age (Years) Height (m) Body Mass (kg)

- - - - - - - - - -

Mean (* SD) 26.4 (I3.29) 1.77 (kO.08) 78.3 (*4.27)

3.2 Adaptations in Performance Outcome with Learning and Retention

Performance tirne, (PT), was the single dependent variable used to evaluate

performance outcome on the motor task by the participants of the experimental and

control groups, within their respective learning and retention levels. Al1 participants

executed each trial with maximum effort and according to the accuracy demands of the

motor task. A one-way repeated measures ANOVA with tests of within-subjects contrasts

applied to the data of the experimental group revealed a significant decrease in

performance time (i-e. 47%) across participants, from pre- to post-learning trials (Le. Day

1 to Day 5) . F (1,9) = 29.3, p<0.0001, as shown in Figure 7A. That is. with learning. each

member OJ=l O) was able to perform the movement faster without sacrificing the end-

point accuracy conditions of the motor task. The slight increase in performance time from

Day 5 to one-week post-learning (Ret 1) was not significant, F (1,9) = 0.2, p<0.649,

indicating that the performance tirne of the experimental group had attained a plateau at

this retention interval. However, the change in performance time from Ret 1 to Ret 2 was

significant, F (1,9) = 10.4, pc0.011, and attested to the fact that the members were

slowing d o m in their movements to the target with two-weeks of no-practice. There

were no other significant differences in the performance times of the group beyond Ret 2,

as demonstrated by the pair-wise cornparisons of Ret's 2-3, 3-4 and 4-5, see Appendix 6.

A two-way repeated measures ANOVA, applied to the 'pooled' data of both the

experimental and control groups demonstrated significant changes in performance time

across post-training and post-retention conditions, F (2,26) = 13.4, pc0.0001, as well as

significant interactions of the data over the same time periods, F (2'26) = 7.3, p4.003

(see Figure 7B). The tests of within-subjects contrasts revealed significant decreases in

PT for both groups fiom Day 1 to Day 5, F (1,13) = 18.2, p<0.001 and a significant

increase and decrease in PT for the experimental and controI groups respectivsly, from

Day 5 to Ret 5, F (1,13) = 8.625, pc0.012. The rate of the decrease in PT fiom pre- to

post-learning conditions for each group was found to be significantly different, F (1.13) =

5.8, ~ ~ 0 . 0 3 2 , with the experimental group showing a much greater index of change (Le. a

47% decrease) than the control group (Le. a 4% decrease). Additionally, the rate of the

A. Performance time - Experimental Group

r

Day 1 Day 5 Ret 1 Ret 2 Ret 3 Ret 4 Ret 5

B. Performaoce Time - Experimental and Control Groups

- -- Day 1 Day 5 Ret 5

Figure 7. Mean performance time (PT) across participants within each of the experimental (N=10) and control (N=5) groups. k PT's of the expenmental group for al1 levels of leaming and retention. B. PT's of both experimental (Exp) and control (Con) groups compared over post-training and post-retention conditions (i.e. fiom Day 1 to Day 5 and Day 5 to Ret 5).

28

changes for each of the groups fiom post-training to post-retention conditions was also

significant, F (1 ,l3) = 8.8, p<0.011. This dernonstrated that the experimental group had

slowed down by the end of the retention period whereas the control group exhibited an

increase in movement speed over the sarne interval, (see Figure 7B and Appendix 7).

3.3 Adaptations in Performance Producrion during both Learning and Retention

EMG measures were acquired fiom the study's participants to provide a

neuromuscular performance index, in ternis of the specific coordination of the muscles

selected as producers of the motor task. The resultant adaptations in motor coordination

due to both leaming and retention conditions would thenceforth provide some recourse to

the rnotor programs of the CNS. An examination of the EMG data in this section will

include a preliminary qualitative interpretation of the muscle activation wavefoms. This

wilI be followed by an in-depth report of the changes in the EMG patterns of the agonist

and antagonist muscle groups within each leaming and retention level using a method of

SVD.

3.3.1 Qualitative EMG Data Analysis

The EMG records employed in the qualitative data analysis consisted of the

ensemble averaging of five trials nonnalized to time base, that is 100 data elements (note:

for the qualitative interpretation, whose focus was purely descriptive, the EMG signals

were presented at each of their non-normalized amplitudes). Of those, elements 40 to 90

relate to the initiation (Onset) and termination (End) points of the motor task respectfully.

Figure 8 represents the linear envelopes corresponding to the agonist (PD, LO, LA) and

antagonist (Pec, Bk, BrR) muscles as exemplified by one participant, P7, before leaming,

on Day 1. The latter muscles are presented as inverted curves in the figure and paired

with their respective agonist counterparts for purposes of clarity as well as to underscore

their antagonistic or reciprocal nature in the motor task. The trials represented within the

figure, proceeded without feedback and followed both the farniliarization and preparation

(i.e. wam-up) penods. The solid line of each plot represents the mean signal whiie the

Motor Task for Participant P7

A. Before Learning (Day 1

END

B. After Learning @ay 5)

Posterior Deltoid r

Pectoralis Major (f ec)

Long Head

Lateral Head of Triceps

I ONSET END - -

Brachioradialis -1 ,b 1

1 1

61 91 1 31 61 91


Figure 8. A sample plot of ensemble averaged (5) muscle activity patterns for the motor task of participant P7. The solid line line represents the mean pattern while the thin vertical lines demonstrate (*) 1 SD. A. Before learning, Day 1. B. After learning, Day 5 .

thin vertical bars demonstrate *1 SD. Also included in the figure are the EMG wavefoms

for the same muscles on the fiAh day @ay 5), following the learning schedule. These

trials were likewise cornpleted without performance feedback by P7. They clearly reveal

that learning was consistent with EMG wavefoms of greater amplitude with more phasic

and distinctive bursts. in comparison to the patterns manifested before learning, the well-

practiced movements were characterized by steeper slopes of the tising EMG signals

concomitant with initial b m t peaks that were located or displaced, earlier in time with

respect to movement onset.

Figures 9-1 3 inclusiveIy, compare the rectified and fiItered EMG data of both the

agonist and antagonist muscles across the post-learninghetention periods for the same

participant. An evaluation of these data demonstrated that at one week post-leaming (Ret

1) there was a decrease in the amplitude of the muscle signals, unlike the greater

amplitude charactenstics of the same EMG patterns observed on Day 5. However, an

additional phase shift of each of the agonist muscles, earlier in time, with respect to

rnovement onset, indicated that there were adaptations consequent to the learning

paradigm which continued to evolve for this individual.

At two weeks post-learning (Ret 2) the agonist muscles for P7 appeared to gain in

amplitude, except for the LA. Nevertheless, these muscles also demonstrated a shift in

phase. later in time, with respect to movement onset, which suggested that they were

being activated at a later time in comparison to Day 5. These changes alluded to a

decrement in the adaptations seen with learning and which had persisted to Ret 1. The

antagonist muscle activation patterns in tum appeared to lose some amplitude in

cornparison to the waveforms of Ret 1. By four weeks post-learning (Ret 3) the PD was

similar in character if not of slightly greater amplitude than at Ret S. Meanwhile. the

triceps muscles were observed to shifi still later in tirne, with the LO decreasing in

amplitude, unlike the LA, which demonstrated an increase in the sarne EMG burst

parameter. The antagonist muscies appeared to be similar in nature as in Ret 2; that is

they had not changed much in terrns of intensity or displacement.

At six weeks post-learning (Ret 4), the agonist muscles showed a slight nse in

amplitude with little shift in phase. The antagonist patterns of the Pec and BrR may seem

3 1

Motor Task for Participant Pl

-4. After Learniog (Day 5) B. One Week Post-Learoing (Ret 1 )

Posterior Deltoid

3

Pectoralis Major

(Pet)

Long Head of Triceps

@O)

Biceps (Bic)

1 Lateral Head

61 91 1 31 61 91


Figure 9. A sample plot of ensemble averaged (5) muscle activity patterns for the motor task of participant P7. The solid line represents the mean signal while the vertical lines demonstrate (*) 1 SD. A. AAer leaming, Day 5. B. One week post-learning, Ret 1 .

Motor Task for Participant PI

A. One Week Post-Learning (Ret 1) B. Two Weeks Post-Learning (Ret 2)

-0.30 1 ONSET

END

Posterior Deltoid

Z / Pectoral is

Major (Pet)

Long Head of Triceps y Lateral Head o f Triceps (LA)

ONSET END

61 91 1 31 61 91


Figure 10. A sample plot of ensemble averaged (5) muscle activity patterns for the motor task o f participant P7. The solid line line represents the mean pattern while the thin vertical lines demonstrate (*) 1 SD. A. One week post-learning, Ret 1. B. Two weeks post-learning, Ret 2.


A. Two Weeks Post-Learning (Ret 2)

-0.30 1 ONSET

1 31

END

B. Four Weeks Post-Learning (Ret 3)


2 L Biceps

(Bit)


Posterior Deltoid

Pectoralis Major (Pet)

61 91 1 31 61 91


Figure 11. A sample plot of ensemble averaged (5) muscle activity patterns for the motor task of participant P7. The solid line line represents the mean pattern while the thin vertical lines demonstrate (*) 1 SD. A. Two weeks post-learning, Ret 2. B. Four weeks post-learning, Ret 3.


A. Four Weeks Post-Learning (Ret 3)

ONSET

B. Six Weeks Post-Learniog (Ret 4)

Posterior Deltoid

Pectoralis Major

(Pet)

Long Head

(Bic)

1 Lateral Head

I

t-'

ENDI / ONSET END

61 91 1 31 61 91


Figure 12. A sample plot of ensemble averaged (5) muscle activity patterns for the motor task of participant P7. The solid line line represents the mean pattern while the thin vertical lines demonstrate (*) 1 SD. A. Four weeks post-learning, Ret 3. B. Six weeks post-learning, Ret 4.


-4. Six Weeks Post-Learaing (Ret 4) B. Eight Weeks f ost-Learning (Ret 5)

-0.30 1 ONSET

END

Posterior Deltoid (PD)

P - Pectoralir Major

(Pet)


Biceps (Bic)


/' ONSET END -É&zzzizG\ - (BrR) I I

61 91 1 31 61 91


Figure 13. A sample plot of ensemble averaged (5) muscle activity patterns for the motor task of participant P7. The solid line line represents the mean pattern while the thin vertical lines demonstrate (+) 1 SD. A. Six weeks post-learning, Ret 4. B. Eight weeks post-leaming, Ret 5.

to decrease whereas the Bic increases in amplitude but these signais too demonstrate

limited displacement. As a result, the limited changes expressed by the muscles at Ret 4

would imply a stabilization or persistence of their features with respect to Ret 3. Finally.

at eight weeks post-leaming (Ret 3, the agonists are al1 of lower amplitude, as compared

to Ret 4, with the LA exhibiting a shifi in phase ahead or earlier in tirne with respect to

the onset of movement. Among the antagonists, the Pec displays a srna11 increase in

amplitude while the Bic and BrR are each observed to decrease in intensity. These

muscles did not reveal any shifts in phase.

3.3.2 EMG Patterns Across Muscles Wifhin Euch Learning and Reîention Level-

Singular Value Decomposition Andysis (SVD)

The singular value decomposition analysis employed on the six processed ELMG

signals (normalized to both 100% performance time and peak amplitude) of each of the

learning and retention periods revealed three wavefoms (W's) that may be used to

explain the six original input patterns. The results of such an anaIysis as exemplified by

one participant, P7, are presented in Figures 14-20. As seen in these figures.

superirnposed upon the six original input EMG patterns are the reconstnicted traces using

only these three W's. Minor deviations fiom the original EMG signais and, in various

instances, close to identical plots are concordant with the error of estimation in using

these waveforms to describe the changes in the levels of both the leaming and retention

conditions.

Each of the W's possesses an eigenvalue, in tenns of a percentage score,

s ipiQing the total variability accounted for by that waveform. ï h e eigenvectors or

muscle coefficients in turn reveal the relative significance of those muscles as represented

by the W. Both the eigenvalues and eigenvectors are relative scores, meaning that each

can be considered as a multiple of the other scores in its category making it possible to

refer to one value as being two or three times another. Plotted in parts B, C and D of

Figures 14-20 are W's 1, 2 and 3 for participant P7 of the before and after learning

conditions, along with each of the five retention periods.

Motor Task for Participant P7: Day 1 Thin Lines: Original Data Thick Lines: Reconstructed Data

BrR: 0.37

LA: 0.54

Pec: -0.48 Bit: -0.38

Pec: 0.28 - w3: PD: -0.32

6.04% C


Figure 14. Sample singular value decomposition analysis on the EMG patterns for the motor task of participant P7 before learning @ay 1). A. Original input activation pattems (thin lines) and reconstructed data (thick lines) using al1 three Waveforms (W's). W's I to 3 including their eigenvalues and eigenvectors are presented in parts B to D. B. WI. C. W2. D. W3.

Motor Task for Participant P7: Day 5 Thin Lines: Original Data Thick Lines: Reconstructed Data - PO

0 100 - ---- LO --- 8 0 - LA

W Pec 60 - --- Bic

A. w

cc - BrR

2 40 -

20 oi O

BrR: 0.40 LA: 0.56

PD: 0.69

B R : 0.17

1 12 23 34 45 56 67 78 89 100


Figure 15. Sample singular value decomposition analysis on the EMG patterns for the motor task of participant P7 aRer learning @ay 5). A. Original input activation patterns (thin lines) and reconstmcted data (thick lines) using al1 three Waveforms (W's). W's 1 to 3 including their eigenvalues and eigenvectors are presented in parts B to D. B. W1. C. W2. D. W3.

Motor Task for Participant P7: Ret 1 Thin Lines: Original Data Thick Lines: Reconstructed Data

w1: Pec: 0.32 \ Bk: 0.35 BrR: 0.39

LA: 0.55

0.3 - PD: 0.54 Pec: 0.21 Bic: 0.28

0.0


Figure 16. Sample singular value decomposition analysis on the EMG patterns for the rnotor task of participant P7 at one week post-leaming (Ret 1). A. Original input activation patterns (thin lines) and reconstructed data (thick lines) using dl three Waveforms (W's). W's 1 to 3 including their eigenvalues and eigenvectors are presented inpartsBtoD.B.WLC.W2.D.W3.

Motor Task for Participant P7: Ret 2 Thin Lines: Original Data Thick Lines: Reconstmcted Data - PD

Pet: 0.30

LO: 0.40 Bic: 0.35

LA: 0.57 BrR: 0.41

Pec: -0.51 Bic: -0.44

O 3 r Pec: 0.16

PD: 0.20 Bic: 0.12

0.0 w3: LO: 0.55 BrR: 0.14


Figure 17. Sample singular value decomposition analysis on the EMG patterns for the motor task of participant P7 nt two weeks post-learning (Ret 2). A. Original input activation patterns (thin lines) and reconstructed data (thick lines) using al1 three Waveforms (W's). W's 1 to 3 including their eigenvalues and eigenvectors are prescnted inpartsB toD. B. W1.C. W2. D. W3.

Motor Task for Participant P7: Ret 3 Thin Lines: Original Data Thick Lines: Reconstructed Data

Pec: -0.50 Bic: -0.34

PD: 0.69 Pec: 0.18 Bic: 0.28

1 12 23 34 45 56 67 78 89 100


Figure 18. Sample singular value decomposition analysis on the EMG patterns for the motor task of participant P7 at four weeks post-learning (Ftet 3). A. Original input activation pattems (thin lines) and reconstnicted data (thick lines) using al1 three Waveforms (W's). W's 1 to 3 including their eigenvalues and eigenvectors are presented inpartsB toD. B. W1.C. W2. D. W3.

Motor Task for Participant P7: Ret 4 Thin Lines: Original Data Thick Lines: Recoastmcted Data

Bic: 0.36 BrR: 0.40

LA: 0.57

3 0.2 - .I

e: 2 Pec: -0.47

Bic: -0.39 c* 0.0 E

C 5 26.17% 4 -0.2 -

PD: 0.70 Pec: 0.26 Bk: 0.27


Figure 19. Sarnple singular value decomposition analysis on the EMG patterns for the motor task of participant P7 at six weeks post-leaming (Ret 4). A. Original input activation patterns (thin lines) and reconstmcted data (thick lines) using al1 three Waveforms (W's). W's 1 to 3 including their eigenvalues and eigenvectors are presented in parts B to D. B. W1. C. W2. D. W3.

Motor Task for Participant Pf: Ret 5 Thin Lines: Original Data Thick Lines: Recoashvcted Data

-- Bic - BrR

55.46% r u

LO LA. ,.,,

4 0.38 . n A* Bic: 0.35

BrR: 0.40

PD: 0.59

Bic: 0.21 BrR: -0.24

1 1 1 1 I 1 I I


Figure 20. Sample singular value decomposition anaiysis on the EMG patterns for the motor task of participant P7 at eight weeks post-learning (Ret 5). A. Original input activation patterns (thin lines) and reconstnicted data (thick lines) using al1 three Waveforms (W's). W's 1 to 3 including their eigenvalues and eigenvectors are presented in parts B to D. B. W1. C. W2. D. W3.

The first waveform, WI, for the above participant accounted for 62.99Y0 and

61.75%, of the total variability before and aller leaming respectfblly. At the end of one

week without practice (Ret 1), the variabitity acounted for decreased slightly to 60.48%

and further to 59.00% by Ret 2. At Ret 3 this value was augmented to 60.79% before

reducing to 56.74% at Ret 4 and settling to a lowest percentage of 55.46% by the end of

the retention period (Ret 5), see Figure 2 1 A.

Unlike the slight decrease in the eigenvalue following learning for P7 above, the

total variability accounted for by W1 increased in 8 out of 10 or 80% o f experimental

members. as a group, Erom Days 1 to 5. The opposite appeared to be tme fiom Day 5 to

Ret 1 with 7 out of 10 people exhibiting eigenvalues for W1 that decreased. Across the

levels of the retention condition there was a tendency for this percentage to rise as 40%.

?O%, 60% and 70% of individuals experienced an increase in the eigenvalue fiorn R 1 -W.

R2-R3. R3-R4 and R4-R5 respectfully, (see figure ZA), in comparison the trend of

declining values demonstrated by P7.

W 1, in this analysis, represented a sort of ' m i n g average' of al1 the input

patterns accounting for muscle coefficients that were al1 positive. W1 is an eigenvector

that is also related to amplitude, representing the strength of i ts pattern within each of the

input signals. A higher load for the LA was evident for P7 on Day 1, before learning.

which was dissimilar to the other muscle activation patterns (0.54 vs 0.34, 0.49, 0.35,

0.30 and 0.37 for the LA vs. the PD, LO, Pec, Bic and BrR respectfülly). The same higher

order eigenvector loading for the LA continued to predominate after learning (Day 5 ) and

throughout the entire retention period, (see Figure 21 B). This shows that for P7, the first

common feature strongly represented the pattern for the LA and highiighted the

importance of this muscle within each of the learning and retention levels of the

experimental period.

Six out of ten or 60% of experimental participants displayed the trend for a higher

load of the LA on Day 1. Likewise, 7 out of 10 or 70% demonstrated a higher weightins

for the sarne muscle on Day 5 (see Figure 218). The predominance of the LA above al1

other muscle coefficients, across the five levels of the retention condition was found in

90%, 70%, 60°h, 60% and 60% of participants in Ret 1, Ret 2, Ret 3, Ret 4 and Ret 5

45

A. Eigenvalue fluctuations for W1 - Experimental group


B. Prominent muscle across participants for W1 - Experimental group

Participant: P 1

PZ P3 P4 P5 P6 P7 Pl3 P9

P l 0

w BrR

LA LA

BrR LA

LO LA LA

LO LA

LA LO LO

LA LA LA LA LOUA

L O LA

Figure 2 1 . (A) Eigenvalue fluctuations and (B) Prominent muscle characteristics for W1 of the experimental group. The bold features highlight participant P7.

respectively (see Figure 21B). Therefore, just as for P7, the uniqueness of the LA pattern,

as revealed by W1, was also a general attribute across experimental participants.

Moreover, for those individuals not displaying a preferential loading for the LA, it was

the LO which predominated arnong the muscle coefficients. The single exception to the

preceding statement was that for Ret 4, the BrR constituted a different muscle, which,

other than the usual appearance of the two triceps muscles in every other experimental

Ievel, dernonstrated its supenority among the agonists and antagonists of two participants.

Regarding the members in the conboi group, the total variability accounted for by

W1 decreased in 3 out of 5 people, increased for one and remained approximateiy the

sarne for another from Day 1 to Day 5 (see Figure 22A). From Day 5 to Ret 5 three

participants displayed an increase in the eigenvalue, as two others showed a reduction in

the latter. In addition, three of five people in the sarne group demonstrated higher muscle

coefficients for the LA on Day 1 while members Cl and C2 each possessed higher LO

loadings for the sarne day (see Figure 22B). On Day 5, C l and C3 displayed greater

coefficients for the LO, whereas C2 and C5 exhibited supenor weightings for the LA.

The PD predorninated arnong muscles in C4 only. At Ret 5 two people possessed higher

muscle coefficients for the LA, two in turn for the LO and one individual displayed a

greater loading for the BrR above the other five muscles (see Figure 22B). The variability

in the eigenvalue fluctuations as well as in the predominance of individual muscle

coefficients within the control group evidently represented nul1 results.

An examination of the eigenvector associated with the second waveform (W2) of

P7. before learning, illuminated an out of phase relationship between the PD (0.62. high

positive loading) and LO (0.32, moderate positive loading) versus the Pec, Bic and BrR

(-0.38, -0.38 and -0.36, moderately high to moderate negative loadings respectively), see

figure 14C. That is, W2 represented the timing of the power of activation between the

agonist and antagonist muscle groups. It was evident that this out of phase relationship

was getting stronger with leaming as the eigenvector coefficients for Day 5 are obsewed

closely (see Figure 15C). Before leaming, the structure of the eigenvector was 0.62 and

0.32 versus -0.48, -0.38 and -0.36 for PD and LO vs. Pec, Bic and BrR respectively.

accounting for 24.04% of the total variability. AAer leaming, the eigenvector coefficients

47

A. Eigenvalue fluctuations for W1 - Coatrol group

Day 1 Ret 5

B. Prominent muscle across participants for W1- Control group

Figure 22. (A) Eigenvalue fluctuations and (B) Prominent musde charactenstics for W1 of the control group.

LhLl IhL5 IkCi Participant:

Cl C2 C3 C4 CS

LO LO LA LA LA

LO LA LO PD LA

BrR LO LO LA LA

were 0.55 and 0.40 versus -0.48, -0.42 and -0.36 for the same muscles as above

accounting for higher variability, 28.3 1%. An increase in the intensity of the out-of-phase

relationship for P7 revealed a greater antagonistic inhibition with learning that was

di fferent from a more prevalent CO-contraction before learning.

At one week beyond practice, the power of the relationship appeared to have

plateaued as revealed by the eigenvector for Ret 1 of 0.55 and 0.37 for PD and LO in

sequence versus the Pec (-0.48), Bic (-0.41) and BrR (-0.38) accounting for 29.3S0/0 af the

total variability. At two weeks post-learning the muscle coefficients dernonstrated a small

increase in the intensity of the out of phase relationship at 0.5 1 and 0.39 vs. -0.5 1. -0.34

and -0.34 concomitant with a diminution in the eigenvalue to 28.12% From 29.38% at

Ret 1. From Ret 2 to Ret 4 the eigenvector loadings did not offer a concrete case for

either the progression or regression of the out of phase pattern. The intensity of the

pattern was more or less maintained, supported by the stabilization of the eigenvalues

frorn 28.12% to 26.37% and 26.17% for the three retention intervals respectively (see

Figures 16C - 19C).

Finally, at eight weeks post-learning the eigenvector was characterized by the

values of 0.50 and 0.25 for the agonist muscles of the PD and LO versus -0.50, -0.44 and

-0.39 for the antagonists of the Pec, Bic and BrR respecthlly (see Figure ZOC). When

compared to the muscle coefficients for Ret 4, an increase in the pattern between the two

muscle groups was evident in spite of an eigenvalue that had not changed measurably

frorn Ret 3. In summary, the eigenvector coef'fïcients, reIating the intensity of the

aforementioned out of phase pattern between muscle groups for P7, clearly divulged an

enhanced antagonistic inhibition with learning that continued to manifest itself at one

week post-learning. However, other than a small increase in the strength of the

relationship at Ret 2, the same muscle coefficients did not reveal any categorical changes

to the relationship with retention. For a report on the eigenvalue fluctuations for W2

arnong members of the experimental group see figure 23A.

Another method of quantifjwg the out of phase relationship between the agonist

and antagonist muscle groups was the evaluation of the delay between the peak and the

valIey of the eigenvector for W2. If a line is vertically drawn fiom both the highest point

49

A. Eigenvalue fluctuations for W Z - Experimental group

7 r - r r -


B. Composite score fluctuations for W2 - Experimental group

-


Figure 23. (A) Eigenvaiue fluctuations and (B) Intensity of the 'Out of Phase' relationship as revealed by W2 for the experimental group. The solid line represents the data for participant P7 while the faint lines descnbe the data for the other members.

(peak) and the lowest point (valley) of the eigenvector to the abscissa or x-mis, which

represents percent performance time, a percentage score is obtained. Subtracting one from

the other provides a composite score that can be used to demonstrate either an increase or

a decrease in the aforementioned relationship. For example, it can be determined that for

Day 1 . the composite score is 28% (76%, the percentage value associated with the lowest

point of the eigenvector, minus 48%, or the value paired to the highest point of the sarne

eigenvector), For Day 5 it is 35%, which therefore represents an increase in the intensity

of the out of phase relationship with learning. For P7 the post-learning level was

maintained at Ret 1 but showed a decrease in the composite score and hence a diminution

in the power of the relationship at Ret 2. Thereafier, the values were not observed to have

changed considerably, see Figure 23 B.

Looking at the entire pool of expenmental participants, the group was found to

display a significant increase in the strength of the out of phase relationship with learning,

F (1.9) = 35.1, p<0.001, and thus an increase in reciprocal inhibition. Furthemore,

fluctuations in the level of intensity of the above pattern during the retention period were

only statistically significant fiom Ret I to Ret 2, F (1,9) = 10.8, pc0.01. At two weeks

post-leaming then, there was a decrease in the values of the composite scores that

promoted a diminution in the level of reciprocal inhibition and an increase in the

antagonistic CO-contraction between the two muscle groups, see figure 23B. There were

no other significant differences in the composite scores of this group beyond Ret 2 as

dernonstrated by the pair-wise cornparisons of Ret's 2-3, 3-4, and 4-5, see Appendix 8.

Changes in the eigenvalues for W2 within the control group can be seen in figure

24A. The percentages did not reveal any significant trends. Altematively, a two-way

repeated measures ANOVA that was conducted on the composite score data that was

pooled over both the experimental and control groups revealed significant adaptations in

the intensity of the 'out of phase' relationship across each of the post-training and post-

retention conditions, F (2,261 = 9.4, p<0.001. The pooled data also demonstrated

significant interactions between the two groups, F (2,26) = 4.3, pc0.025. The tests of

within subjects contrasts exhibited significant increases in the power of the relationship

for both groups fiom pre- to post-learning trials, F (1,13) = 12.2, p<0.004. The tests also

5 1

A. Eigenvalue fluctuations for W2 - Control group

B. Composite score fluctuations for W2 - Experimental and

15

Control groups

-

Day 1

12 I

Day 1 Day 5 Ret 5

Day 5 Ret 5

Figure 24. (A) Eigenvalue fluctuations for the control group and (B) Intensity of the 'Out of Phase' relationship for both expenmental (Exp) and control (Con) groups as revealed by W2.

divulged a significant decrease and increase in the intensity of the pattern for the

experimental and control groups respectively, from post-learning to post-retention

periods, F (1,13) = 5.5, pc0.036. The rates of the increases seen in the out of phase

relationships fiom Day 1 to Day 5 for each of the groups were not statistically different, F

(1,13) = 0.2, pc0.634. However, the rates of the changes describing a reduction in the

intensity of the pattern for the experimental group by the end of the retention protocol. in

contrast to the continuing increase in the power of the relationship for the control group.

was found to be significant, F (1,13) = 10, p<0.007 (see Figure 24B and Appendix 9).

The third waveform, W3, for P7 accounted for 6.04% and 4.39% of the variability

before and after learning in sequence. Thereafier the eigenvalue rose to 5.96% at Ret 1

and increased fiirther to 8.30% at two weeks post-learning before falling to 6.98% four

weeks afier training. At Ret 4 there was an increase in the variabiiity accounted for to

8.74% and 9.49% by Ret 5.

W3 explained the remaining variability of the three wavefoms used to interpret

the EMG data. In other words, after the variability for both W 1 (a running average of the

muscle activation patterns with a stronger representation of the LA) and W2 (out-of-

phase relationship between agonist and antagonist groups) is removed, what remains is

the variability associated with W3. Even though the eigenvalues for W3 are low, as seen

above for P7, the fact that there exist opposing polarities of the eigenvector coefficients

within each of the agonist and antagonist groups made it evident that this waveform

represen ted the complex contrasts among the individual muscles within each group.

An observation of the eigenvector of P7 for Day 1, before learning, divulged the

LA (0.56) with a high positive loading in contrast to the PD (-0.32) which had a

moderately low negative weighting coefficient among the agonists; the LO (-0.07) was

essentially, not represented. The Bic (-0.69) with a very high negative coefficient differed

in polarity from the Pec (0.28), whose low positive weighting, along with the BrR's

(-0.14) very low weighting, made each of these muscles within the antagonist group

negligible.

An examination of the shape of the waveform for W3, on Day 1, dispiayed a more

local pattern of the motor task, whose amplitude was concentrated within the latter half of

53

the movement (Le. between 50 and 100 points of percent performance time). The local

pattern seemed to portray the high positive loading of the LA and more importantly, the

very high negative loading of the Bic (-0.69), see figure 14D. Consequently, before

learning, P7 demonstrated an antagonist representation of the motor task with a relatively

weaker contribution of the agonist muscles.

After learning, on Day 5, each of the PD (0.69) and LA (-0.61) had increased

remarkably in magnitude and maintained their contrasting polarity, attesting to the strong

latency between them. The LO (-0.22), although demonstrating an increase in its

coefficient as compared to Day 1, was still at a relatively low and negtigible weighting. In

contrast, there was little, if any, presence of the forearm flexors (0.24, 0.17 and 0.13 for

the Bic, BrR and Pec respectfully). The waveform on Day 5 was evidently sinusoidal and

eshibited a more global pattern of the task that was distributed over the entire

performance time. At this point the amplitude of the waveform appeared to be

concentrated within the initial half of the task (Le. between 1 and 56 points of percent

performance time). As a result, following learning, P7 demonstrated an essentially

agonist representation of the motor task owing to the negligible presence of the

antagonists (see figure 15D). An examination of the agonist pattern revealed a proximal

to distal relationship defined by the very high positive loading of the PD versus the high

negative loading of the LA. This interpretation of the latter muscles on Day 5, wouid

seem to quali@, in retrospect, the agonist representation on Day 1 as a weaker or

underdeveloped proximal to distal relationship since the LA was shown to be the

predominant muscle in contrast to the PD before practice.

With one week of no-practice the PD maintained its contrasting polarity with the

LA but was lower in magnitude at 0.54, with respect to the latter muscle which had

become much more prevalent at -0.76. The small gain realized by the LO afier learning,

had effectively been compromised at Ret 1 (LO: 0.1 1). Among the antagonists, there was

no representation for the BrR (0.01), as the Bic and Pec possess low weighting

coefficients (0.28 and 0.21 respectively). The global, sinusoidal shape of the waveform

was maintained at Ret 1 that continued to depict an agonist characterization of the

'strategy' employed by P7 to produce the motor task. However, the lower eigenvector

54

loading of the PD in contrast to the higher weighting of the LA revealed what appeared to

be a decrement in the strength of the proximal to distal pattern-

At two-weeks post-leaniing the agonist portrayal changed with the LO (0.55)

corning into prominence at a high positive loading in opposition to the LA at -0.78, a very

high negative coefficient. The PD (0.20) was conspicuously reduced in its presence

among the extensor muscles at this time which was readily observed by a leveling out of

the eigenvector for Ret 2 (see figure 17D). Consequently, the LO muscle seerned to take

on the role of the PD in describing the proximal to distal timing of the activations

between the two triceps muscles. All of the antagonist muscle coefficients remained

insignificant here.

At four weeks beyond the completion of training (Ret 3) the flexor group was still

conspicuously absent. Within the extensor group however, the PD had increased

substantially in its loading and was positive at 0.69, in relation to the LA and LO each at

a high (-0.56) and moderate (-0.32) negative weighting, respectively. It appeared that at

this time the proximal to distal pattern had become re-energized as evidenced by a greater

latency between the PD and the combined activation of the LA and LO muscles which

demonstrated an increase in synergistic activation. The aforementioned pattern also

appeared to persist through to Ret 4, except for the LO, whose eigenvector coefficient

decreased to the point of being negligible (see figures 18-1 9D).

At the end of the retention period, the PD decreased in weight to 0.59 as the LO

displayed itself at a very high negative loading of -0.69. There was no representation for

the LA however, which had consistently demonstrated a strong latency with respect to the

proximal joint agonist in each of the preceding experimental sessions. It would appear

that the LO muscle supplanted the LA in characterizing the proximal to distal pattem

upith the PD. Each of the Pec (0.27), BrR (-0.24) and Bic (0.21) remained, as throughout

the retention penod, at low weighting coefficients.

In sumrnary, for this participant, W3 remained global and unchanged for the

majority of the retention penod; except for Ret 2, which demonstrated a virtual absence

of the PD. Moreover it was dominated particularly by the extensor group and depicted the

contrast of the firing pattem between the PD versus the LA and LO. According to the

55

eigenvector coefficients, this pattern deteriorateci at two-weeks pst-training after which it

appeared to make a corne back at four and six weeks of no-practice. It seemed to dirninish

in strength again by Ret 5 (eight weeks post-leaming). The eigenvectors of al1 three

waveforms (Le. W1, W2 and W3) for participant P7, within each of the learning and

retention conditions, are presented in Table 2.

A complete depiction of the within muscle group contrasts of al1 experirnental

members, is provided in Appendices 10 - 13. Appendix 10A shows the agonist ancüor

antagonist representations of the rnotor task fiom Day 1 to Day 5, before and after

learning respectively. The actual data (Le. the eigenvector coefficients) o f t he

a forernent ioned muscles depicted in the preceding Appendix are avai lable in Appendix

10B. Appendices 1 1 - 13 include the within muscle group characterizations of the rnotor

task, as well as the eigenvector coefficients of the muscles for both the short- (Day 5 to

Ret 2) and long-term (Ret 3 to Ret 5) retention intervals. Within each of the these figures

the muscles are presented in order of decreasing magnitude according to their respective

coefficients. This was done in order to highlight those muscles contributing most to the

production of the motor task. They do not necessarily imply an order of muscle firing

unless otherwise stated. instead they cornrnunicate the relative importance or significance

of each muscle within the agonist and/or antagonist pattern of the particular learning or

retention condition (see page 1 26).

Across experimental participants, learning also resulted in significant phasic

adaptations to the sequencing of the muscle activity patterns within the agonist muscle

group in particular. It revealed a general increase in the pattern of the proximal t o distal

activation of these muscles, in eight out of ten people (80%: P2-P9), which contributed to

an improvement in motor performance. At the sarne time, the level of antagonist

involvement was observed to decrease for the majority of experimental members (70%:

Pl-P2, P4, and P6-P9). The latter was demonstrated by a reduction in either the

magnitude or the nurnber of eigenvector coefficients for the muscles highlighted as

significantly contributing to the motor task on Day 1. The muscles which remained

representative within the task after learning consisted of either the Bic or BrR.

TABLE 2

Eigenvectors of each of the three waveforms, W1, W2 and W3, for al1 levels of learning and retention for the motor task of participant P7

1 Muscle 1 Day 1

PD 0.34 Pec 0.35 L O 0.49 Bic 0.30

1 BrR 1 0.37

Day 5 Retl 1 Retz 1 Ret3 1 Ret4 1 Rets

Muscle

1 Pec 1 0 . 2 8 1 0 . 1 3 1 0 . 2 1 1 0 . 1 6 1 0 . 1 8 1 0 . 2 6 1 0 . 2 7 1

Muscle l

w2 Day t 1 Day 5

I

Day 1

Ret4 1 Ret 5

1 1

Ret 1

Day 5 Ret4

Ret 2

Ret 1 Rets

Ret 3

Ret 2 Ret 3

The above mentioned recession of antagonist activation within the motor task

reinforced the significance of the agonist representation and suggested the apparent

'strategy' of the neuro-rnotor system: to program the initial propulsive characteristics of

the motor task so as to engage only the appropriate or sufficient arnount and/or timing of

antagonist activity. Furthemore, the degree to which the magnitude of the relationship

between the PD versus the LO and LA is expressed, is not the same for everyone but

specific to the individual performing the task. In other words people will leam to petfom

the motor task with varying extents of muscle activations owing to simple individual

di fferences.

Certain exceptions among the members of the experimentai group were

noteworthy, however, such as for P8, who was singular in his portrayal of a global pattem

of the third waveform (W3) before practice. The pattern highlighted a rather distinguished

proximal to distal relationship of the PD (-0.66) versus the LA (0.41) and LO (0.38) on

Day 1, apparently superseding the involvement of the Bic (-0.42). Members P4 and P l0

also displayed a similarly conspicuous proximal to distal agonist pattern on Day 1, before

practice, but whose wavefonns were characteristic of the local pattern described

previousIy (see Appendix 10A and B). With learning, the agonist representation did not

change for P4 and P8, instead the power of the relationship between the muscles becarne

stronger as evidenced by the eigenvector loadings for both participants (P4: 0.61 vs. -0.5 1

on Day 1 and 0.65 vs. 4-71 on Day 5 for the PD versus the LA respectively and f8:

-0.66 vs. 0.41 and 0.38 on Day 1 with respect to 0.61 vs. -0.47 and -0.43 for the PD

versus the LA and LO respectively). In addition, P l0 was the only person to convey a

decrease in the intensity of the agonist representation with learning in favor of a Full

complement of antagonist muscles involved in the task, see Appendix 10A and B.

Other interesting findings included the antagonist representations of participants

P6 and P9 before training, which exposed a dissociation of the Pec (a proximal joint

horizontal adductor) versus the Bic and/or BrR (muscles primarily associated with elbow

flexion). The differentiation of these muscles on Day 1 would suggest a proximal to distal

activation concerned with arresting the initial propulsion characteristics of the brachium

by the PD and the resulting extension of the fore- to the target as effected by the LA

58

andior LO muscles. It was observed that following training, these same individuals

simpli fied the manner in which they stopped the whipping movement by mostly enlisting

the action of the Bic, a two-joint muscle, which may have acted at both points of the two-

joint system.

Across the short-tenn retention intervals, the data of the third waveform for the

experimental group provided results that corroborated the findings of the second

waveform which, as previously noted, described a persistence of the adaptations between

muscle groups at Ret 1, and a decrement in the latter at two weeks post-learning. The

third waveform revealed a majority (i.e. 60%) of experimental members (P3. P5. and

P7-P IO) who also exhibited a persistence or even an improvement in the within muscle

group adaptations fiom Day 5 to one-week post-learning. These included a maintenance

or enhancement of the power of the proximal to distal relationship and a continuing

abatement in the significance of the antagonists during the motor task (Le. P3, P5, P7-

P 10. see Appendix 1 1A and B). Some exceptions to the preceding declarations included

P9 who showed an irnprovement in performance based on a substantial decrease in

performance time, from 255.4 msec on Day 5 to 208.8 msec at Ret 1. Underlying the

decrease in performance time was an agonist representation of the LA (-0.55) versus the

LO (0.50) muscle that introduced the latter as a significant proximal joint agonist in the

motor task. Participant P l 0 was also exceptional within the experimental group at Ret 1

in that he demonstrated a fortified antagonist sequence of the BrR (-0.77) versus the Bic

(0.54) and Pec (0.31) cornmensurate with a total dissolution of the agonist muscle

presence (see Appendix 1 1 A and B).

The four rernaining individuals, Pl-P2, P4 and P6, exhibited decrements in motor

performance at one-week post-learning that were characterized by either a weakening of

the proximal to distal pattern of the agonists and/or a resurgence of a significant

antagonist presence in the motor task. It is important to note, however, that the

diminut ion in coordination expressed by three of the aforementioned members did not

necessarily demonstrate regression to pre-training levels. The within muscle group

representations of these people (N=3) still promoted certain adaptations acquired with

learning. Participant Pl for instance, showed that the LA muscle, which solely

59

distinguished the agonist representation on Day 5, continued to present itself as a

preeminent muscle within the agonist group at Ret 1. P2, who exhibited a reduction in the

degree of the proximal to distal pattern of the agonists at Ret 1, nonetheless continued to

show an absence in the antagonist presence that was specified with learning on Day 5 . in

addition. P6 retained a degree of the proximal to distal character of the agonists. after

training, in the form of the LO versus the LA, in spite of a reappearance of the antagonist

muscles which were observed to characterize the motor task on Day 1. In fact, P4 was the

only person to display a complete reversa1 of adaptations at the end of one-week without

training, see Appendices 10 - 11, A and B.

At two-weeks post-learning, however, 60% of individuals (Pz. PS, and P7-P10)

demonstrated decrements in the within muscle group characterizations which, like the

results in the second waveform above, provided fùrther evidence of a limit to which

adaptations in motor ski11 acquisition remained unaffected by a termination in training.

For P2, P5 and P7-P9 the decline in performance entailed a decrement in the status of the

proximal to distal nature of the agonists and a reaffirmation of the antagonist presence in

the motor task with respect to the within muscle group characterizations of the previous

retention interval (see Appendix 1 1A and B). Participant P l0 on the other hand, reverted

to a greater representation of the agonist muscles in a proximal to distal sequence of

activation, which was similar to that exhibited on Day 1.

The data of the long-term retention penods, however. did not necessarïly reveal

that the diminution in neuromuscular coordination observed at Ret 2, marked the

beginning of a progressive decrease in performance over Ret's 3 - 5. Rather, in each of

Ret7s 3, 4, and 5 there were 70% of experimental participants who exhibited either

persistent or slightly augmented levels of motor performance in comparison to the degree

of coordination displayed at Ret 2 (see Appendices I l - 13, A and B). The improvements

in movement production were usually accompanied by decreases in performance time but

these values, which were sometimes better than the counterpart times at Ret 2, were never

lower than the PT'S demonstrated at Ret 1. In other words, the instances of an

enhancement in performance within experimental members across the long-tenn retention

penods were indicative of individual residual improvements in motor coordination that

60

TABLE 3

Eigenvalues, percent variability accounted for (* 1 SD) by eacb waveform and the sum of al1 three W's within both learning and retention levels

for the motor task of the experimental group (N=10)

Da' 1

Day 5

Ret 1

Ret 2

Ret 3

Ret 4

Ret 5

SUM W1-3

were restricted to these intervals. They did not represent superior performances in relation

to those observed at Ret 1 , the last indication of a persistence or improvement in the

neuromuscular adaptations acquired with leming.

Table 3 displays the average variability terms for each of the wavefonns of the

SVD analysis (Wl, W2 and W3) as welt as the surn of a11 three, for the entire

experimental group, within each Iearning and retention level. Although the changes

observed for the individual waveforms were not conspicuous, the sum of al1 the

wavefoms put together demonstrated an increase in the variability accounted for with

leaming and a decrease in the variability accounted for at the end of the retention period.

These data confirmed the tower variabiiity in the EMG waveforms as a result of the

training regimen and an increase in the variability of the muscle activation patterns after

eight weeks of detraining.

Appendix 14A presents the within muscle goup characterizations of the control

group fiom Day 1 to Day 5 . The actual data for the muscles depicted in the figure is

available in Appendix 14B. Four out of five individuals clearly dernonstrated a local

pattern of the waveform for W3 on Day 1, while a fiflh person was singular in the

exhibition of a global pattern of the waveform for the sarne day. Similar to the findings of

the expenmental group above, before practice, the local pattem of the four control group

members (N= 4) portrayed a significant presence of the antagonists in deference to a

weaker contribution of the agonist muscles. The magnitudes of the antagonist coefficients

ranged fiom -0.31 (C4: BrR) to 0.85 (Cl: Pec) see Appendix 14B. Among the five

rnembers of this group, C 1 , C4 and CS show the presence of one antagonist muscle, as C2

and C3 demonstrate two and three antagonists respectively.

On Day 5, four out of five rnembers displayed a global pattem of the wavefonn

for CF3. Only one person, C l , continued to show a local pattem characterizing the motor

task whose within muscle group representation was identical to Day 1. Therefore,

equivalent to the changes expenenced by the majority of the expenmental group, the

aforementioned subgroup (N= 4) of control participants conveyed an increase in the

power of the proximal to distal relationship cornmensurate with a diminution in the roles

of the antagonist muscles.

At Ret 5, al1 of the control group members portrayed a global shape of the

waveform for W3, which communicated an ongoing manifestation of the intensity

conceming the proximal to distal pattern of the agonists developed by Day 5. A

reconstitution of the antagonist presence was also apparent however, indicating a retum

to the significant involvement of these muscles in the motor task, as was previously noted

on Day 1, and hence a small but notable regression in petformance. The fact that the

control group displayed a persistence of some of the acquired adaptations expressed on

Day 5 further attested to the learning effect in this group in spite of a minimal amount of

exposure to the motor task (see Appendix 11B).

The averaged variability tenns for each of the three waveforms and the surn of al1

three together for the five members of the control group are presented in Table 4. The

data showed an increase in the variability accounted for fiom Day 5 to Ret 5. which

demonstrated a higher contribution of the second waveforrn (W2).

TABLE 4

Eigenvalues, percent variability accounted for (* 1 SD) by each waveform and the sum of al1 three W's across post-training and post-retention

periods of the control group (N=5)

L

Day 1 W l

62.2 1 (12.63)

W2 22.78 (13.79)

W3 8.37

(* 1.76)

SUM W1-3 93 -3 5 (* 1 -23)

CHAPTER IV

The current study empioyed electromyographical techniques to assess the neural

activations of six muscles of the left upper limb during both leaming and retention

protocols. These EMG signals constituted mesures of performance production that were

analyzed by a method of singular value decomposition. SVD analysis permits the

examination of entire wavefoms as opposed to discrete evaluations conceming the time

series of the data, which observe only portions of the actual muscle activity patterns, (e-g.

onsets and offsets, threshold levels etc.). Consequently, it is a useful method in describing

the phasic information of the muscle activity patterns being anaiyzed. Moreover, the

identification of a minimum number of common patterns or wavefoms underiying the

EMG data is consistent with the reduction of degrees of fieedom theory in motor control

as proposed by Bernstein (1967). That is, similar to Bernstein's theory, the SVD analysis

seeks to generate a minimum number of control pattems whose changes across both

learning and retention levels of the current experiment c m elucidate the modifications in

the neural input to the muscles being analyzed.

Of the six original input patterns to the SVD process, three wavefonns were

extracted fiom the data to describe the neuromuscular adaptations to motor ski11 learning

and retention. As alluded to above, the aim was to illuminate the CNS strategies

goveming the reduction of degrees of freedom with learning as theorized by Bernstein

( 1 967) and more importantly, to determine how these strategies change with increasing

penods of no-practice.

The results of this investigation are discussed within sections delineating the

learning adaptations of the experimental group as a fùnction of the practice protocol first.

This will serve as a preface to the subsequent evaluation of the effects of both short- and

long-term penods of no-practice respectively, on the coordination of the muscles

goveming the task. The changes associated with the control group will be dealt with

separately, at the end of the chapter.

The expenmental participants in the current study achieved the principle criterion

of leaming, namely a significant decrease in performance time. Even though the motor

task consisted of a relatively simple whipping movement, the volunteers were able to

improve their execution of an as fast as possible action to an extemal target over

successive days of the learning paradigm. It is important to note that although the

mechanical aspects of the motion are easily reproducible, the requirement of perfonning

to the limits of one's maximum efforts entails a vigorous challenge for the neuromuscular

system. Consequently, investigations into apparently simple movements are valuable

when inquiring into the underlying processes and products of movement (Gottlieb et al.,

1988; Corcos et al., 1993; Vardaxis, 1996).

When studying multi-joint movement in particular there is always a question

regarding the representation by the sample of muscles selected for analysis. In this

investigation six muscles were chosen according to each of their primary and/or

secondary îùnction as an agonist (PD, LO and LA) or antagonist (Pec, Bic and BrR) to

the motor task. A simple way of looking at this sarnple is to consider pairs of reciprocal

muscles in the same anatomical location that possess antagonistic roles. For instance. the

PD and the Pec can both be observed as the proximal, single-joint muscles involved in

horizontal abductiodadduction. The former contracts concentrically first. to decrease the

posterior angle of the shoulder while the latter follows with an eccentnc contraction, to

control the increasing anterior angle of the same shoulder. Likewise the LO and Bic are

both two-joint muscles that cross each of the shoulder and elbow articulations. In order,

they fiinction as a secondary agonist and antagonist to the proximal joint respectively. as

well as to the distal joint, the elbow. Finally, each of the LA and BrR share in their

unique actions at the distal joint, as a primary elbow extensor and flexor respectively. The

above muscles were chosen as being representative of the motor program used to produce

the task. There are other muscles of the upper limb, shoulder and postenor back regions,

which contribute to the movement, however these muscles are located deep within the

lirnb and shoulder complex (e.g. media1 head of the triceps, brachialis, coracobrachialis

and pronater teres) which would preclude the use of surface electrodes.

4.1 Adaptations of the agonist and antagonist muscle groups with learning

The leaming protocol employed in this study was successful in determining

changes conceming the neural activations of the muscles composing each of the agonist

and antagonist groups. The SVD analysis appropnately revealed those changes, as

observed by the three wavefoms used to explain the muscle activation patterns

contributing to the production of the motor task. It is meaninghl to discuss the 'number'

of wavefoms involved since they are orthogonal and independent one from the other.

sharing no covariance between them. The first waveform (Wl) had, associated with it.

eigenvector coeficients that were al1 positive across both pre- and post-learning

conditions. This communicated the fact that W1 constituted a 'nuuiing average' of the

original EMG pattems, representing the strength of the W 1 waveform within each of the

original input pattems. The shape of the waveform before leaming appeared to possess

two 'humps', of which the second was larger than the fint. They seemed to reflect the

temporal locations of the initial agonist EMG bursts followed by those of the antagonist

muscles (see Figure 14A and B). At the end of training, the waveform had a more

'rounded-out' look (see Figure 15B). It clearly attested to EMG bursts that had become

more phasic, with earlier and faster rise times in relation to the onset of movement

(particularly among the extensor muscles), whose areas were considerably larger than

before training (see Figures 8 and 15B). Although there was a general increase in the

eigen~ralues for W 1 across experimental participants, From pre- to post-learning settings,

the magnitude of the changes with leaming were not pronounced (see Figure 2 1 A, Day 1

to Day 5). The inconspicuous nature of these results was interesting since qualitative

observations of each of the six muscles for an example participant (P7) categoncally

attested to the effects of training on the muscle activation pattems, as referred to above

(see Figure 8).

Among the muscles represented by W l , the LA was one that demonstrated a

higher eigenvector coefficient above al1 other muscle coefficients from pre- to post-

learning trials for the majority of experimental participants (see Figure 21B). The

prominence of this muscle probably indicated its importance in extending the forearm to

the target of the motor task following the initial propulsion of the Srachium by the PD

and/or the LO. This could be explained by the fact that the angular displacement required

at the elbow (90 degrees of extension from the initial starting position) to reach the target

was greater than that of the shoulder (45 degrees of horizontal abduction from the initial

holding position). These results concur with the findings of Wadman et al., (1980) who

demonstrated that for the muscles having a real contribution to the movement under

investigation, the duration of the agonist excitation was longer for a larger movement.

Thus the LA, as the single-joint elbow extensor, wouId be central to the task.

Furthemore, it is possible that a stretch reflex was elicited from the LA muscle, during

the initial acceleration of the brachium by the proximal joint agonists, that could have

placed the former muscle on stretch. It is well known that a muscle which is piaced on

stretch, to a certain degree accorJing to the length tension relationship of the specific

muscle, responds with a more forcefil contraction (Kreighbaurn & Barthels, 1985).

It is interesting to note that the LO exhibited the second highest eigenvector

coefficient arnong the muscles studied from Day 1 to Day 5 and was often quite close to

the magnitude of the value for the LA. This may reflect the LO's dual nature in the motor

task as horizontal shoulder abductor and elbow extensor, such that it could have been

assisting in each of the aforementioned actions during the performance. Once again.

however, in view of the greater amplitude of movement required at the elbow in the task,

i t would be plausible to assume that, like the LA, the LO was being recruited as an elbow

extensor rather than as a shoulder abductor. As a result, it couId have also experienced a

stretch reflex during the motor task that would help explain its comparable muscle

coefficients, with respect to the values of the LA. Any comments related to the actual

strength of the above muscles, as a contributing factor to their superior manifestation

within the eigenvector, would be speculative since no pre- or post-learning strength

measures were taken.

Although the amplitude of a muscle's EMG activity can be equated with the

muscle's force characteristics (Woods & Bigland-Ritchie, 1983), there are a number of

factors associated with surface EMG recording that should be taken into account when

interpreting such a parameter. These include the variability in the fiber-type composition

of different muscles, the low-pass filtering effects of larger skinfolds as well as the inter-

electrode distance of bi-polar configurations (Bilodeau et al., 1990). In this investigation.

the EMG patterns were normalized to peak amplitude before the SVD analysis, a process

that would preclude an evaluation of the amplitude characteristics of the signals and

hence a measure of the force characteristics of the muscles. As a result, only the phasic

effects of the muscle activation pattems assayed during both the learning and retention

protocols were capable of being analyzed. An increase in the strength of the muscles

following the practice penod is possible however, considering that strength

training/detraining paradigms have alluded to the prospect of increasing neural

adaptations prior to actual muscle fiber hypertrophy (Hakkinen & Komi, 1983; Narici et

al.. 1989).

Moreover, researchers have found a preferential hypertrophy and an increase in

the integrated EMG activity of individual muscles within the same muscle group

following a strength training regimen that alluded to a different fraction of the total force

of the muscle group being exerted by these muscles (Narici et al., 1989). This knowledge

emphasizes the importance of ascertaining the strength levels of the muscles being

investigated in movement studies, throughout the experimental period, in order to clearly

assess their precise roles in producing the motor task in question (van Bolhuis & Gielen.

1997).

The appearance of the second waveform, (W2), was sinusoidal with an initial

positive peak located in the fint half of the task followed by a negative peak present in

the second half of the motor task. The eigenvector coefficients for W2 were divided into

positive scores for each of the PD, LO and LA muscles within the agonist group and

negative scores for the Pec, Bic and BrR muscles of the antagonist group. Both the shape

of the waveform and the division of the coefficients along sign lines underscored a

synergistic activation of the agonist and antagonist muscles with an activation lag

between the two groups. Specifically, this cornmon feature highlighted the out-of-phase

relationship regarding the PD and LO versus the Pec, Bic and BrR which exhibited a

higher CO-contraction between the two muscle groups before learning (see Fisure 14C).

-4cross experimental participants the eigenvector coefficient for the LA muscle

possessed a minimal weighting which revçaled that it did not share in the synergy

expressed by the other two agonist muscles. The proximal origins of the PD and LO

would apparently explain the increased covariation between these muscles and dictate a

greater latency of their EMG bursts with respect to the patterns and, in particular, the nse

times of the antagonists. It is not that the LA burst or its rise time was not distinctively

separated from each of the shoulder and f o r e m flexors, but rather to a slightly lesser

degree as compared to the other two agonist muscles. In fact for one particular individual

(participant P l ) the rise time and presence of the LA burst was actually in the same

temporal location (Le. in the second half of the motor task) as each o f the antagonist

bursts. on Day 1. This was substantiated by an eigenvector loading for the elbow extensor

that was negative and approxirnately of the sarne magnitude as the other shoulder and

elbow flexor muscles. Furthemore, it is interesting to note that the LO was not

represented equally with the PD in terms of its eigenvector loading and. for al1

experimental participants, was always o f a lower weighting with respect to the latter

muscle. Once again, this is probably due to its position within the proximal to distal

hierarchy of the agonists; that is, within the motor task it was the secondary shoulder

extensor after the PD.

With leaming, the phasic effect, as revealed by the shape of the wavefonn,

became very clear among the experimental participants, demonstrating a decrease in

antagonistic co-contraction in light of an increase in reciprocal inhibition between the

agonist and antagonist muscle groups (see Figure 15C). This was also observed by a

general increase in the eigenvalues and eigenvectors of the SVD analysis for most

members. Some participants did not show significant gains in either o f the two SVD

parameters but inspection of the original data wavefoms and the eigenvectors for CF2

unequivocally revealed the changes brought about by motor task practice. As described

within the Results chapter, an evaluation of the delay between the 'peak' and the 'valley'

of this waveform and therefore of the activation lag between the agonist and antagonist

muscles provided a more meaningfùl portrait of the intensity of the out of phase

relationship. In particular, al1 members displayed an increase in the strength of the

relationship with practice that was statistically significant ( p c O.OS), see Figure 23B and

Appendix 8.

The third waveform demonstrated a local pattem of the motor task before

practice, in al1 but one of the experimental participants (P8). This pattem was defined by

a greater amplitude of the waveform towards the latter half of the task (i-e. tiom 50% to

100% performance time) as was seen in Figure 14D for participant (P7). The eigenvector

coefficients of W3 displayed values of contrasting poluities among the muscles within

each of the agonist and antagonist muscle groups. This evidently revealed that the nature

of W3 was to illuminate the individual roles, or more specifically, the activation patterns

of the within group muscles with respect to the production of the motor task.

The initial local concentration of the waveform before practice appeared to

convey two things: (1) the slowly rising slopes of the agonist EMG signals cornmensurate

with burst peaks that were closer to the onset of movement (see Figures 8 and 14A) and

(2) the preerninence of either one or a combination of antagonist muscles that were

involved in the task (see Appendix 1OA and B). On Day 1, six out of ten (PLP3, P5, P7,

and P9) or 60% of experimental members exhibited a dissociation between the PD versus

the LO and/or LA in which the latter muscles possessed a greater eigenvector loading. It

would appear that before practice, these participants subscribed to a proximal to distal

strategy that entailed a greater emphasis of the triceps muscles in the production of the

task (except for P4 and P l 0 who possessed a higher Pdel coefficient in relation to the LA

and the LA and LO coefficients respectively, see Appendix 10A and B). Furthemore. the

lesser amplitude of the first half of the waveform, that is associated with the agonist

muscles and which is temporally located at about the onset of movernent (Le. at 40% PT),

suggested that, for this penod, the proximal to distal characterization was essentially

underdeveloped.

For the same members above (N=6), either the Bic or BrR (i.e. the antagonist

muscles operating at the elbow joint, including the distal aspect of the biceps, a two-joint

muscle) was shown to be central in slowing down and/or stopping the limb's excursion to

the target (for P4 it was the Pec). This finding would be an appropriate complement to the

greater representation of the triceps muscles within the proximal to distal relationship of

the agonists described above. That is, the increased action of extending the elbow to

accelerate the forearm to the target would require an enhanced activation of the

antagonists subserving the elbow joint, to decelerate the distal limb. Concerning the result

of participant P4, a representation of the Pec (-0.51) would entai1 a logical selection for

this person who demonstrated a higher magnitude of the PD coefficient (0.61) in

opposition to the LA muscle (-0.5 1) within the agonist muscle sequence. An activation of

the proximal joint antagonist would seem necessary against the more forcehl action of

the abducting brachiurn produced by the leading role of the PD. This, however. was not

the case with P8 and P l 0 who also exhibited a predominating PD in their proximal to

distal pattern- Instead each of them demonstrated the Bic muscle as the preferential

antagonist in the motor task.

In two out of ten memben (P6 and P9) the local pattern of the waveform

characterized an even greater involvement of the antagonist muscie group. P6 displayed

the Pec versus the Bic, which outnurnbered the single LA of the agonist group, whereas

the Pec versus the Bic and BrR outnurnbered the PD versus the LO for P9. In fact, the

dissociation of the Pec fkom the Bic (a two-joint muscle) and/or the BrR, according to the

polarities of the eigenvector loadings for these muscles, actually demonstrated a proximal

to distal relationship of the antagonists. The greater magnitude of the Bic within the

aforementioned pattern of each of these individuals still highlighted the increased role of

the muscle among the antagonists in the motor task, as it had for the other participants

above. These findings are both unique and meaningful, in that they support the proximal

to distal programming of the agonist muscles discussed previously. For instance. the

sequential firing of the Pec versus the Bic and/or BrR would be necessary to decelerate

and stop the initial propulsion characteristics of the brachium, to get the two-joint system

moving, followed by the angular velocity of the forearm in that order. Moreover, the

greater angular velocity of the forearm. as dictated by the increased actions of the LA and

LO muscles for P6 and P9 respectively, explained the superior manifestation of the Bic to

counteract and brake the increasing angle at the elbow. For these volunteers then, the

presentation and/or coordination of the antagonists in arresting the movement of the limb

revealed a strategy that was equally as important if not more so than the initial commands

to get the ann moving to the target.

Finally, the facility with which P8 performed the motor task on Day 1 afler oniy

15 farniliarization trials was remarkable (PT: 185 I 1 msec). The outnght expression of

an unequivocally strong PD (-0.66) in contrast to the synergistic activation of the LA

(0.4 1 ) and LO (0.3 8) muscles before practice signalled the neurornotor systems capacity

to appropriately identiQ the prescriptions for action relating to a supenor rnotor

performance with minimal practice. In fact McGrain (1986) found similar evidence for

the application of an apparently suitable motor program to a novel motor task when

investigating a knee extension movement. In this study participants were required to push

a four wheel carriage through a timing gate located eight feet away at a criterion speed of

5 mph. There were no significant changes observed in either total movement time or

timing of EMG activity for two muscles across twenty practice trials of the task.

According to the author, the simplicity of the motor task may have resulted in the

seIection of a movement strategy which had established the necessary timing of EMG

activity for both muscles from the very beginning. The implication was that the

participants were able to sense the timing of muscle activity needed to perform the task

before they had executed the first trial. Therefore. even though P8 had no pnor

experience in the motor task of the current study, the participant was able to 'get a good

idea' of the timing characteristics required for a good motor performance after the first

few trials of the task.

With learning the shape of the waveform for W3 changed considerably for al1

experimental participants, into a global pattern whose augrnented magnitude spanned

across the entire task. It clearly revealed the development of the contrast in the firing

between the PD versus one or both of the triceps muscles, confinning the proximal to

distal strategy selected before learning. Other researchers have shown similar evidence

concerning the sequential progressions of initial agonist activations from axial joints to

peripheral ones (Wadman et al., 1980; Karst & Hasan, 1991; Vardaxis, 1996). This

sequencing of segmental rotations is more commonly known as the kinetic link principle

and is used for such patterns of movement as throwing, kicking and striking wherein the

action of the moving system is likened to the motion of a whip (Kreighbaum & Barthels,

1985). It involves an initial rotation of a stable base segment that is followed by a

fonvard rotation of the next distal segment. The latter only comes forward afier the

proximal segment has reached its peak angular velocity. Consequently, this scenano

creates an effect on the distal segment that is referred to as a 'lag'. In athletic situations.

the 'lagging back' of the distal segment@) is produced by a preliminary reversal in the

motion of a system most commonly observed as a 'wind-up'. Within the context of this

study's experimental task, which did not include a wind-up, a comparable lagging of the

foream may have been engaged by a progression of the brachium out and ahead of the

distal segment, a process called inertial lag (Kreighbaum & Barthels, 1985). As was

discussed earlier on in this chapter, it was the inertial lag of the forearm that may have

evoked a stretch reflex in each of the triceps muscles.

There were eight members who demonstrated the kinetic link principle via a

fortification of their agonist muscle sequences after the practice protocol. Five of these

people led with a hlgher muscle coefficient of the P D (P3, P5, P7, P8 and P9) whereas

three others possessed greater eigenvector loadings of one or both of the triceps muscles

(Pz, P4 and P6). In the latter three cases, the P D also showed an increase in its role in the

task with respect to Day 1, by virtue of a cornmensurate augmentation of its coefficient.

Alternatively, two individuals were unique in their portrayal of either a single highly

weighted LA or a prominent dissociation concerning the Pec versus the Bic and BrR.

respectively. These results communicated the effects of individual differences in the

performance of motor skills, such that the sequence of muscle activations for a particular

movernent are not necessanly the same and that participants will seek to enhance

performance in different ways (Corcos et al., 1993; Magill, 1993). ïhese findings are not

surprising since the members in this study were given no instructions about any particular

moLrement strategy that would assist them in their planning and/or execution of the motor

task. They were free to proceed at their own discretion.

Motor task practice also had the effect of diminishing the roles of the antagonists

in eight out of ten (80%) volunteers fiom pre- to post-leaming conditions, for which the

remnants of antagonist activity still featured the Bic or BrR acting at the elbow joint

(except for P i who displayed the Pec). Two others, P3 and P5, on the other hand.

revealed an increase in antagonist presence (see Figures 18 and 19). The general decrease

in the importance of the antagonist muscles following learning may reveal the CNS's

operation of economizing ancilor reducing the problem of the complexities of movement.

In other words, confronted with this study's novel whipping task, the above people were

initially more occupied with arresting the primary propulsion characteristics of the

agonists. Following the practice protocol, however, they learned to engage the

appropriate amount of whipping action to perfom the motor task more quickly and

efficiently without enlisting any greater a complement of antagonist muscles than was

necessary, In this manner, a simple decrease in the number of antagonist muscles

exploited during the execution of the motor task would indicate that the available

numbers of degrees of fieedom had been reduced by the CNS.

Additionally, an analysis of the cumulative variability accounted for, by the

eigenvalues of al1 three wavefoms (W's 1,2 and 3) put together, revealed that the value

for the expenmental group was higher on Day 5 than it was on Day 1 (Table 3). This

suggested a decrease in the variability of the muscle activation patterns with learning and

reinforced the fact that the participants had achieved a level of mastery in the motor task

which allowed them to perform in both an efficient and expedient manner.

4.2 Motor Task Retention Adaptations of the Agoni* and Antagonist Muscle

Groups: Functional Stages of S h o ~ - und Long-Term Motor Memory

In this study, a time-course evaluation of motor task retention was undertaken in

order to reveal the relative stability of the motor memory programs associated with

complex motor skill acquisition. The strength trainingdetraining literature of exercise

physiology research contains significant information regarding the impressionability of

strength-training induced adaptations to increasing periods of detraining (Hakkinen &

Komi, 1983 and 1985; Narici et al., 1989; Ishida et al., 1990; Staron et al., 1991 ).

However, these results have also alluded to certain selective, complex, post-training

adaptations which referred to a persistent alteration of the motor memory prograrn

subserving the particular motor skill. In fact 'periodization' of training schedules.

involving a reduction in one or more strength training variables such as volume of

training, has even shown improvements in motor skill performance to subsequent testing

or cornpetition (Hakkinen et al., 199 1 ).

Furthemore, more recent investigations in motor control have documented the

lasting effects of motor skill learning (e.g. over several months). These studies have

focussed on the neural mapping of motor memory correlates using functional M N and

Pet scans of rapid finger sequencing (Kami et. al., 1995) as well as of adjusted pointing

movernents to the torque pulses of a robotic manipulandum (Shadmer & Holcomb, 1997;

Shadmer et al., 1997). The above research will be used to help put the results of the

curent study into context.

4.2. I Short-term Changes l n Motor Memory

With one and two-weeks of no-practice respectively, neither did the shape of the

waveform for W1 nor the representations of the eigenvector coefficients conceming the

agonist and antagonist muscle groups. change measurably with respect to Day 5. Al1 of

the scores remained positive with unequivocal fluctuations in their magnitudes across the

two retention conditions for al1 memben of the expenmental group (for example. see

Figures 16 and 17B of participant P7). At the same time it was curious to note that 90%

of the people displayed a higher eigenvector loading for the LA at one-week post-

learning as opposed to 70% seven days later at Ret 2, see Figure 21B. The fact that there

were no changes conceming the eigenvalues, eigenvectors and waveforms of W1 for the

short-term memory conditions communicated the need to go beyond this waveform in

order to delineate how these retention intervals affected the memory of the motor task.

Changes in the 'out of phase' pattern between the agonist and antagonist groups

for the participants as a group, over Ret's 1 and 2, were difficult to ascertain using the

eigenvalue fluctuations and the structure of the eigenvectors across experimental group

members. However, statistics performed on the composite scores of the second

waveform, which revealed no significant differences in the tests of within subjects

contrats regarding the means fiom Day 5 (38.70%) to Ret 1 (38.10%), highlighted the

sisnikant decrease in the means From Ret 1 to Ret 2 (36.40%), p<0.009. These results

demonstrated a persistence of the intensity of the out of phase relationship with one-week

of no-practice. Therefore, the increase in antagonistic inhibition experienced with

learning was not lost or otherwise compromised seven days following the interruption of

practice. In this study, though, fourteen days rnay have constituted too long a time

without practice before the enhanced reciprocat inhibition between muscle groups was

influenced. indicating regression toward antagonistic CO-contraction.

The apparent extension of the increased latency between the two muscle groups at

Ret 1 begs the clarification of whether the ten retention trials (i-e. 5 preparation and 5

stable adaptation trials) were suffkient to comprise a retraining stimulus for the

volunteers. It is meaningful to consider since each of the participants did not correctly

achieve the first five stable adaptation trials sequentially and required more trials to attain

the criterion of tive. In particular, for each of the short-term retention periods as well as

the pre- and post-leaming trials of the control group, al1 of which occurred within a one-

week interval, the opportunity for additional trials could have constituted a factor limiting

the e ffec tiveness of the study 's treatment, namely abstinence from practice. Although the

above resdts concerning W2 may confirm that these 'extra' trials did not re-engage the

Iearning process or affect the retention intervals differently, the possibility that they could

have remains a question to be addressed in this investigation.

The third waveforrn (W3) was also sensitive in exposing changes to the Ieamed

adaptations of the motor task during the short-term periods of no-practice. To begin with,

the eigenvecton of the third waveform disclosed alterations of the within muscle group

relationships suggesting a lapse in motor coordination in only four people (PLP2, P4.

and P6) after the first retention interval. When cornpared to Day 5, the characterizations

of the agonist and antagonist muscles for these members were similar, although not

identical, to those exhibited on Day 1, before practice. They either manifested a

weakening of the proximal to distal relationship of the agonist muscles alone (Pl. P2), or

together with the reappearance of a significant antagonist presence (P4 and P6), (see

Appendices 10 and 11A and B). Researchers have previously alluded to the fragile

nature of short-terrn motor memory as revealed by the incomplete retention of both

simple and complex motor skills from one expenmental session to the next (Le. 24 to 48

hour intervais; Corcos et. al., 1993; Vardaxis, 19%).

It is important to note that although in the latter studies, the participants' next day

performance had been slightly beiow the peak attained at the end of the preceding day. it

was nonetheless above the level of performance exhibited at the b e g i ~ i n g of the

previous day. A between learning levels analysis was not performed in this investigation;

even so, similar findings of short-term motor memory lability should not be precluded in

this case. By extension, it would seem appropriate for the results of these participants

(N= 4), at one week post-learning, to reflect a cumulative effect of several days without

practice and hence a decrement in the coordination of the muscles producing the task.

Nevertheless, in three out of the four people for whom the latter situation was tme, rnotor

performance had not necessarily regressed to pre-training levels (e.g. P1-P2, and P6).

Wolpaw et. al., (1986), in their spinal stretch reflex studies have indicated that a major

function of supra-segmental control is to suppress spinal reflexes. This would

understandably allow for the perseverance of acquired skillful movements (Goode & Van

Hoeven, 1982). It may also underlie the observations of why the three participants still

exhibited some retention (however limited) of the learned adaptations of the motor task at

Ret 1. In other words, the CNS facilitates the acquisition and subsequent retention of the

motor commands having to do with skiIlfiil movements. This has a1so been demonstrated

within strength training/detraining paradigms conceming the selective persistence of

absolute measures of fast force production and maximal dynamic strength. These values

had decreased but were still greater than pre-training levels at 12 and 30-32 weeks post-

detrainhg respectively (Hakkinen & Komi, 1985; Staron et al., 1991). P4 was the only

individual of the above subgroup (N= 4) who displayed a complete reversa1 in learning

adaptations, experiencing what investigators of the detraining phenomenon would define

quite simply as " an effect comparable to the opposite effects of training" (Hakkinen &

Komi, 1983 and 1985).

The fact that the majority of experimental members (i.e. 60%: P3, P5 and

P7 - P10) showed a persistence or even an improvement in motor task performance at

Ret 1, further illuminated the capacity with which the CNS strives to replace the initial

pre-leaming rnotor comrnands with new ones borne out of deliberate and specific

practice. As a result, this group (N=6) confirmed that one week without training was not

deIeterious to the neuromuscuIar coordination acquired with training. Moreover, these

findings corroborated the results of the second waveforrn, which also revealed a

persistence and/or improvement in the learned adaptations for the experimental group at

Ret 1. Indeed as Brashers- h g et. al., (1996) and Shadmer & Brashers-Krug (1997)

have found with adjusted pointing movements, an interna1 mode1 (IM), which associates

a particular pattern o f muscle torques with the desired trajectory of a motor skill, is not

only stabilized but consolidated in rnotor memory at approximately 4 hours afler practice.

Thus people who learned the motor task were able to perfonn better on recall tests at 24

hours and up to three-weeks beyond training.

In accompanying experiments, the sarne authors tested the stability of the

acquired IM by intervening with a second, different, motor task following learning of the

initial one (i.e. retrograde interference). It was revealed that 5.5 hours between the two

tasks was sufficient time to allow for a significant recall of the first IM at one-week post-

training. When 24 hours had elapsed before the second task was introduced, recall of the

first IM approached the performance index of controls who had only practiced the first

task. Ishida et. al., (1990) have also suggested that short-term strength training may

actually lead to rather significant post-training adaptations (i-e. consolidation), regarding

an increase in the maximal rate of force development in the human triceps surae muscle

at four and eight weeks post-detraining. Thus, it would appear that in the present

investigation, the majority of experimental participants had consolidated the prescriptions

for action associated with the motor task in motor memory and that the motor program

itself was seemingly resistant to forgetting for up to a one week period without practice.

At two weeks post-leaming, however, the experimental group featured six

participants (P2, P5 and P7- P10) who expenenced decrements in their motor

coordination, with respect to the leamhg adaptations engendered with practice and

maintained over a one week penod, as described above. These individuals (N=6)

eshibited a deterioration in the proximal to distal relationship of the agonist muscles

including an increased representation of the antagonists [e-g. for P2 (BrR: -0.52) and P9

(Pec: 0.68 vs. the BrR: -0.47), see Appendix 1 1A and BI. The attenuation in the proximal

to distal sequencing of the agonist muscles together with the greater involvement of the

antagonists probably alluded to the decreasing acceteration and increasing deceleration

profiles of the movement. Consequently, the PT for these individuals was observed to

increase, indicating that they were slowing down.

These generahzed results of a decrease in motor performance with no-practice

would appear to agree, in principle, with the findings of strength trainingdetraining

paradigms, concerning the reversible nature of training-induced adaptations. In the

aforernentioned investigations, common decreases in: maximal dynamic or isometnc

contraction forces, associated neural activations (Le. maximum integrated EMG' s) and

size andlor percentages of fast twitch fibers (type IIa) are usually observed when the

training stimulus has been removed for up to 12 weeks. The changes however, were not

to pre-training levels (Hakkinen & Komi, 1983 and 1985; Narici et al., 1989; Staron et

al., 1991).

A reversa1 in the participants' adaptations within the current study at Ret 2

suggested a decay in the motor prograrn subserving the task. Whereas an upper limit in

the stabiiity of the motor program consolidated in rnemory was estabfished at one week

post-learning, two weeks without training was apparently too long a time to keep the

program from deteriorating. Moreover, the data of the third waveform afforded hrther

evidence against the argument that the re-testing trials of the retention conditions

provided an additional stimulus to the participants, which may have contributed to a

further improvement in their performance. If these trials were re-engaging the learning

process, then the trials executed within the first retention session (Ret 1) should have

reinforced the temporal sequencing features of the muscles involved in the task to curtail

any decrements in the motor prograrn at Ret 2; this was not the case.

4.2.2 Long-term Changes in Motor Memory

Across each of the long-term retention conditions, fiom four to eight weeks

beyond the completion o f training, the general shape of the first waveform (WI) did not

reveal any significant changes. Also, the characteristic preeminence of the LA muscle

within the majority o f the eigenvectors among the experimental participants was

maintained.

An analysis of the composite scores conceming the second waveform did not

revea1 any significant effects among the intervals of the long-term motor memory period

(see Appendices 12 - 13, A and B). In fact the fluctuations in the values fiom nvo- io

eight weeks post-learning were very small and did not provide any notable increase or

decrease in the out of phase relationship between the two muscle groups. Consequently.

the status of the last meaningful alteration in the out of phase pattern, regarding the

decrement in reciprocal inhibition expenenced from Ret 1 to Ret 2, remained the modus

operandi for each of Ret's 3 ,4 and 5 .

Modifications, in the phasic adaptations of the muscles within each of the agonist

and antagonist groups, as delineated by the eigenvectors of the third waveform, did not

necessarily expose any progressive deterioration in motor coordination across

participants. Lnstead, in each of Ret's 3, 4 and 5 there was a majority of expenmental

members who demonstrated either a persistence o r even an improvernent in motor

79

performance with respect to the preceding long-term retention period. Wi th few

exceptions the observed irnprovements in performance were accompanied by decreases in

performance time; however, the reductions in PT were never greater than the PT'S

exhibited on Day 5 or at Ret 1. This clearly indicated that the improvements in movernent

production were probably the result of compensatory adj ustments to the prevailing

coordination of the muscles involved in the motor task. In other words, in view of the

findings concerning a probable decay in the motor program at Ret 2, the participants who

returned for testing during the long-term retention penods were likely trying to make up

for the decrement in performance that they were experiencing. To that end, they used

whatever rnernory of the skill was still available to hem, in addition to any extra 'cues'

they could get from both the preparatory and stable adaptation trials at the time of the re-

testing sessions to execute the task as quickly and as accurately as possible.

The changes observed in the cumulative variability accounted for by the surn of

the three waveforms across the retention conditions were not very large but a decrease in

the values by the end of the retention period indicated an increased variability among the

EMG patterns (see Table 3). This reinforced the finding that the experimental participants

were no longer perfonning with the sarne certainty in the motor task as they had been on

Day 5 and Ret 1, periods which characterized a greater automaticity in their motor

responses.

4.3 Ch anges in the Performance Production and Outcome Measures

of the Control Group

The effects of the control group protocol in producing adaptations among its

members over the leaming condition of the experimental penod (i.e. Day 1 to Day 5) that

were sirnilar to the changes observed in the experimental group were unexpected but not

totally surprising. The changes in the adaptations for each of the groups over the retention

period (i-e. Day 5 to Ret 5) , however, were different and alluded to a superficial leaming

effect in the control group. To begin with, the twenty scheduled trials afforded to the

control members on Day 1 were evidently sufficient to stimulate the organization of a

motor program that accommodated the temporal features requirements of the motor skill.

An analysis of the composite scores fiom the second waveform (W2) for both

80

experirnental and control groups demonstrated that the difference in the rate of increase

in the intensity of the out of phase relationship observed from Day 1 to Day 5 was

statistically insignificant. Nevertheless, the experimental group sti 11 exhi bited a much

greater index of change (Le. a 20.6% increase) with training as opposed to the control

group (i-e. a 5.6%) which did not receive specific training in the task. Similarly, the

control group succeeded in exploiting the proximal to distal strategy of muscle activation

among the agonists and reduced the activation of the antagonists, to decrease their

performance time. However, inspection of the percent changes in PT measures over both

groups from Day 1 to Day 5 showed that the experimental group realized a 47% decrease

in PT as compared to the 4.3% reduction attained by the control group. Therefore, even

though the control group displayed adaptations in both performance production and

outcome measures fiom Day 1 to Day 5, these changes were substantially smaller than

the adaptations experienced by the experimental group as a result of the training protocol.

From Day 5 to Ret 5, the trends in the changes observed for each of the two

groups were found to be significantly different. For instance, the experimental group

experienced a reduction in the intensity of the out of phase relationship between the

agonist and antagonist muscle groups that indicated an increase in antagonistic co-

contraction. The majority of participants within this group also exhibited a regression in

the adaptations of the within muscle group relationships which showed that the proximal

to distal pattern of the agonists was weakened and that there was an increase in the

activation of the antagonists in the motor task. As a result, the overall performance time

of the experimental group was observed to increase fiom post-training to post-retention

trials. In contrast, the control group demonstrated an additional increase in the out of

phase pattern for the second waveforrn and a decrease in performance time over the same

interval. Moreover, an increase in the cumulative variability accounted for, by the sum of

al1 three waveforms for this group, indicated that the muscle activity patterns for the Ret

5 condition had becorne less variable than on Day 5 (see Table 4), which supported the

ongoing improvement in motor performance.

Consequently, the differences in the results of each group were significant in

highlighting a functional level of learning for the expenmental group and a superficial

level of acquisition for the control group. That is, participants in the former group had

achieved a degree of mastery in the motor task for which the consequences of terrninating

practice entailed a decrement in motor performance. In contrat, the members of the

control group had procured a comparativeiy limited degree of task proficiency that

defined a substantial performance reserve. It would explain their inclination to improve

upon a performance level on Day 5 that was not very high to begin with.

CHAPTER V

SUMMARY

The current research investigated the retention charactenstics of the acquired

neuromuscular adaptations in a fast complex motor task. Specifically, the aim of this

study was to elucidate the stability of the temporal sequencing of muscle activations

subserving the movement in motor memory, when specific training in the task has been

terrninated. Furthemore, how Bernstein's degree of freedom theory applied to the

changes in rnotor coordination during retention of the motor task, was aiso assessed. ft

was presumed that eiectromyographic activity provided a 'gateway' to the central

processing of the neural commands to the muscles involved in the motor task. It was

h)~othesized that the between and within muscle group adaptations with leaming would

be compromised during the retention penod.

In this study an experimental group cornprising ten participants was trained over a

four day learning protocol to execute targeted arm movements in the horizontal plane at a

maximal speed. They were re-tested at 1, 2, 4, 6, and 8 weeks following the end of the

leaming period which constituted the retention protocol. The first two weeks post-

leaming were categorized as a 'short-terni retention period' while a 'long-term retention

penod' was defined by four to eight weeks post-learning. A control group was also tested

in the motor task at pre- and post-learning conditions as well as at the end of the retention

penod for comparative purposes. Surface electromyography was used to monitor the

electrical activity of six muscles of the iefi upper limb and chest. EMG electrodes of a

bipolar configuration were placed directly over the bellies of the posterior deltoid,

clavicular pectoralis major, long and lateral heads of the triceps brachii, long head o f the

biceps brachii and brachioradialis. A reference electrode was placed over the right

clavicle. A method of singular value decomposition (SVD) was employed to determine

the minimum number of waveforms required to describe the set of six muscle activation

patterns.

5.1 Concluswns

Experimenfal Group

( 1 ) The learning protocol resulted in significant decreases in performance time for the

motor task, among the participants in the expenmental group. This performance

outcome rneasure appropnately defined motor skill acquisition in this

investigation.

(2) The learning protocol produced an increase in reciprocal inhibition between the

agonist and antagonist muscle groups in the motor task that detennined a decrease

in antagonistic CO-contraction within the shoulder and elbow joints involved in the

movement.

( 3 ) Learning enhanced the proximal to distal activation of the agonist muscles across

the shoulder and elbow joints and reduced the number and/or intensity of

antagonist muscles that were significantly exploited in the motor task. A decrease

in the representation of the antagonists with learning fulfilled Bernstein's theory

conceming a reduction in the degrees of freedom of movement with motor skill

acquisition.

(4) The re;ention protocol resulted in significant increases in performance time for

the motor task beginning at two weeks post-learning of the short-term retention

period. This performance outcome rneasure provided the first index of a

decrement in the motor performance arnong participants.

( 5 ) The retention protocol revealed a diminution in the reciprocal inhibition between

muscle groups observed with learning at two weeks beyond the completion of

training, in light of an increase in antagonistic CO-contraction within the shoulder

and elbow joints subserving the movement.

(6) The retention protocol also demonstrated that the learning adaptations of the

within muscle group relationships were compromised at two weeks post-learning.

The decrements included a weakening of the proximal to distal pattern of

activation arnong the agonist muscles and a relative resurgence in the number

and/or intensity of the antagonist muscles in the motor task. An increase in the

representation of the antagonists indicated a reversal in the reduction of the

nurnber of degrees of freedom with learning.

(7) The motor task was simple enough to engage significant improvements in both

the performance outcome and production measures of the control g r ~ u p .

Nevertheless, these adaptations characterized a superficial leaming of the motor

task arnong these members and reinforced the efficacy of the learning protocol for

the experimental group, which resulted in the achievement of a functional levei of

mastery in the motor task for the latter.

5.1 Recommendations for Future Research

The current study has raised some pertinent issues for tuture investigations into

motor skill learning and retention that include: (1) the nature and complexity of the motor

task employed in the research, (2) the performance index required of the participants and

(3) the skill level of the individuals taking part in the study.

First, the nature of the motor task used in the research must be explicitly specified

and categorized in order to allow for appropriate comparisons with the findings of both

existing and tiiture studies using similar tasks. For instance, the complex g r o s motor

whipping movement involved in the present study did not Iend itself entirely to

comparison with the majority of pointing andhr reaching movements of motor control

research. Therefore, more study is required on the ballistic tasks that are inherent in many

athletic skills such as throwing, kicking and striking with or without an implement-

Second, the practice or training used within a learning protocol must realize a

performance plateau in the participants involved, to eliminate any question of a

performance resenre among the individuals. This would allow for a clear delineation of

the performance level in a motor task and facilitate the comparison to other experimental

sessions a d o r members. For instance, in the current study, although the experimental

group members exhibited substantial improvements in performance time, there was no 85

guarantee that these changes necessarily characterized the performance peak within each

of these individuals.

Finally, an account needs to be made conceming the ski11 level andor prior

experience of a prospective participant so that the results of an investigation are

appropriate to the treatment adrninistered and not confounded by the particular abilities of

the individuals comprising the experimental group.

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Appendix 1

LITERATURE REVIEW

A review of the related literature to the major topics of the present study will be

categorized as follows: firstly, a preliminary discussion of the electromyographic (EMG)

activity involved in motor skill learning will ensue as it pertains to single- and multi-joint

actions respectfully. Considering that true expressions of single joint movements are rare

in 'real', everyday activity, the focus on such laboratory based tasks does provide a

fundameatal assessrnent of the operation of the central nervous system (CNS) during

movement production. As a resutt, they are a necessary starting point to building a

progressive understanding of more complex ideas, such as when enquiring into the

electrophysiological dynamics of multi-segmental systems.

Secondly, a presentation of the information pertaining to motor skill retention, as

i t applies to the context of this investigation, will conclude the review.

EMG Adaptations of Single- and Multi-Joint Movements with Practice

Simple Movements

A biphasic or triphasic muscle activation pattem has been consistently

documented in the literature with respect to simple voluntary goal-directed movement

that is rapidly executed. As early as 1926 (Wacholder ar,d Altenberger), an initial agonist

volley (AGI) was observed to be followed by a 'quiet period' of reduced electncal

activity during which time the antagonist (ANT) woutd fire. A second agonist burst

(AG2) terminated the electrical event.

If fast, high speed or skilled ballistic trajectories are characterized by the above

motor output pattern (Hallet & Marsden, 1979; Lestienne, 1979; Brown and Cooke.

1980; Mustard & Lee, 1987; Brown & Gilleard, 1991), slow movements display a more

continuous agonist excitation in light of a diminished or complete pause of antagonist

activity (Patton & Mortenson, 1970; Hallet et al., 1975; Lestienne, 1979). Even slower

speed rarnp movements are manifested by agonist/antagonist CO-contraction.

The role of each of the EMG components as they relate to the kinematics of a fast

movement can be described as follows: AGI constitutes the propulsive force initiating

targeted limb movement, while the subsequent 'silent period' is apparently reciprocally

matched by ANT which attenuates the limbs acceleration in a deceleratory phase. AG2 as

the tertiary burst is also present during limb deceleration and may assist in stabilizing the

joint at its terminal end-point position.

The etiology and functional significance of the triphasic pattern within the CNS

has heretofore received comprehensive attention. Numerous investigators have proposed

a central origin for AG1 and ANT whereas the strong variability accrued in the assay of

AG2 has attested to its penpheral mediation (Garland & Angel, 1971; Garland et al.,

1972; Angel, 1974; 1975; 1977; Hallet et al., 1975). Regardless of the apparent pre-

construction of the first two EMG bursts however, researchers employing various

perturbations and paradigms of movernent have exploited the impressionability of these

vo1leys to segmenta1 manipulation (Hallet & Marsden, 1979; Brown & Cooke, 1980;

Waters & Strick, 1981; Berardelli et al., 1984; Sanes & J e ~ i n g s , 1984). Thus central

commands issued as starting points to a movement could still be modified at the

periphery according to the later properties of an action.

Using electromyography, researchers such as Person (1956) and Kamon &

Gormely (1968) studied the changes in muscle activity that accompanied the skilful

performances of sorne 'real-life' and athletic tasks. For instance, during early training of

filing and cutting with a chisel, Person observed the simultaneous activations of triceps

(agonist) and biceps (antagonist) muscles that were central to the tasks, arnong

participants.

Specifically, early movements were affected by an increased activation of the

agonist when the antagonist was excited a? the same time, resulting in erratic,

unrhythmical actions. After training, rhythmical manifestations of the movements were

CO-ordinated by reciprocally prograrnmed onsets and offsets of agonist and antagonist

volleys. Hence, the principle forcehl nature of the triceps and the ulterior corrective role

of the biceps (in braking the movement at specific times) were clearly delineated within

the tasks respectively.

In novices executing a gymnastic single-knee circle mount on the horizontal bar,

Kamon and Gomley witnessed the EMG bursts of several muscles investigated in the

hip, tmnk and amis which were characterized by extended durations contributing to

frequent overlapping or CO-contraction before training. As the panicipants performed the

exercise more fluently in the terminal stages of practice. however, there was a greater

incidence of sequential activations arnong muscles (Le. decreased CO-contractions) which

were ful filling more speci fic roles in the motor task.

Payton and Kelley (1972) devised a pilot study to determine the EMG

charactenstics o f the anterior deltoid and biceps brachii with the learning of a novel ball-

tossing task. Expenmental participants, who were fitted to a straight-backed chair, had a

Ieather cuff secured upon the forearm o f the dominant arm, which was placed in the

anatomical position. Attached to the cuff was a plastic cup containing a standard ping-

pong ball. The aim was to propel the ball to a target bucket whose rim was 76 cm away.

Both the shoulder and elbow joints were fiee to move. A decrease in the total electrical

output and in the rise time for the biceps, regarded as the focal muscle in the task, was

found with learning in cornparison to a non-significant increase in the activity of the

proximal joint agonist.

Experiments by Hobart, Kelley and Bradley (1975) used a similar method of an

underhand ball-tossing task to describe the movement changes with learning and funher

elucidate the electrophysiological manifestations subserving the action. To that end they

restricted the movement to the shoulder joint and an assay of the anterior deltoid and

pectoralis major as agonists versus the posterior deltoid and triceps brachii as antagonists

in the task. The target consisted of a 72 square inch board of concentnc circles with a

common centre. It was 150 cm away fiom the base of a throwing chair and at an

inclination of 22 degrees fiom the floor. Following 150 trials of the task, experimental

participants had decreased the limb angle at bal1 release while perfoming at higher

velocities early on in the movement to reduce both their throwing error and movernent

tirne. A decrease in the total electrical activity of the anterior deltoid with no change in

the pectoralis was observed concomitant with a decrease in the time to reach peak activity

by both agonists. These changes figured prominently in providing a greater impulsive

force to augment the velocity profile of the limb early on in the movement. Altematively.

increased activity in each of the antagonist muscles and a decreased latency of the

posterior deltoid, with respect to the onset of its agonist counterpart, contnbuted in

reducing the higher initial velocity of the limb and to release the bal1 earlier at an

increased velocity.

Payton, Su and Meydrech (1976) elaborated on the significance of the apparent

equivocal activity conceming the prime movers of a motor task fiom pre- to post-leming

conditions. To that end they restricted their focus on only the abductor digiti quinti of the

fifih digit in a shuffleboard type task. They found that sets of 100 trials used to reach a

learning cntenon provided no statistical difference between the E-MG data of the pre-

practice and post-practice trials. They concluded that the results reinforced a hypothesis

originated with the findings of Payton and Kelley (1972); narnely that the agonists

pertaining to a task resolve fiom a previously 'undifferentiated field of muscles' into the

prime movers and auxiliaries of a movement. The former, remain at a comparable level

of electrical activity as the latter show a decrease in activity with motor ski11 leaming.

In cornparison to previous results, however, specifically those upon which the

hypothesis was originally predicated, the postdates do not necessarily represent the

findings. For instance, in the pilot study by Payton & Kelley, it was the biceps, a two-

joint muscle, which was singled out as the probable prime mover in propelling the ball to

the target. Although no data was collected regarding the onset times of either the anterior

deltoid or the biceps, it would be plausible to suggest that it was the proximal joint

agonist that fired first providing the initial displacement of the brachium. As a result, it

likely possessed an assisting role in the task to guide the proximal limb to the target. In

that case, the biceps, as the principle mover. would be inclined to demonstrate no

particular change in activity, according to the hypothesis, while the EMG activity of the

anterior deltoid or auxiliary muscle, would decrease. The reverse was actually m e ; it was

the biceps, which decreased in activity, as the anterior deltoid experienced no significant

change. It would appear that the unrestrained elbow in the task precluded a clear

delineation of which muscle possessed the prime mover role. Indeed, in the investigation

by Hobart et al., above, a forearm splint restricting movernent to the shoulder, which

clearly exposed the anterior deltoid as the prime mover, also demonstrated a decrease in

totaI electncal output of the latter muscle. The pectoralis, another agonist, which actually

played a supporting role, displayed no change in its activity.

Additional research by Hobart, Vorro and Dotson (1978) reproduced the method

of the bail-throwing task used by Hobart et al., (1975), to investigate the dynarnics of

motor ski11 acquisition. The results of various kinematic and EMG variables were

analyzed at five separate intervals of a practice period totalling 104 trials of the task (Le.

trials 1-4, 26-29, 5 1-54, 76-79 and 10 1- 104). Statistically significant decreases in

throwing enor, movement time, iimb angle at ball release and in the time to peak velocity

of the limb, were found to occur within the first 25 tosses. Not surprisingly. these ieamed

adaptations were sirnilar in nature to those observed in the aforementioned study since

the same task was employed. In contrat to those reports though, there was no change in

the total integrated activity of either the anterior or postenor deltoid muscles, which had

previously shown a decrease and an increase in total electrical output respectively.

Nevertheless, a decrease in the latency of the posterior deltoid, an antagonist, was still

demonstrated which continued to support the importance of muscle timing (or the

sequencing of muscle activation) in de fining the changes associated with learning.

Vorro and Hobart (1981a-b) extended their research with the ball-tossing task to

two separate distances, 90 and 150 cm and analyzed a total of eight muscles, 6 agonists

and 2 antagonists.The practice of 103 trials was distributed into seven blocks (block 1:

throw 1, block 2: throws 2-3, block 3: 13-15, block 4: 26-29, block 5: 5 1-53, biock 6: 76-

79, block 7: 101-103). Moreover, they employed a regression equation to determine the

relative importance of a nurnber of kinematic and EMG variables, which best described

the acquisition of the motor ski11 at each of the designated distances. The investigators

noted that the greatest decreases in uirowing error also occurred early on in the practice

period, this time afier only the first two training blocks (Le. 15 trials).

The first equation underscored a large initial adjustment in the total electrical

output of both agonists and antagonists to increse the limbs veIocity at ball release and

contribute to its deceleration respectively, within the first three trials of the task. The

second equation, related to the changes between the first and second training blocks,

profferred significant increases in the initial velocity of the limb as well as a decrease (90

cm goup) and an increase (150 cm group) in the limb angle at ball release. Subserving

these aforementioned kinematic variables were pnmary increases in the pre-movernent

times of the agonists including an augmented synergistic activation of these muscles to

propel the limb toward the target. These were followed by a decreased latency of the

antagonists to decelerate the limb. Further modifications in the above variables, fiom

blocks 3 to 7, were considerably smaller than the adaptations reported between the first

two; they retlected only minor alterations in rnyo-temporal sequencing.

Ludwig (1 982) investigated the triceps and biceps muscles in horizontal extension

movements of the non-dominant ann dunng learning of a shuffleboard task by

participants whose aim was to propel a puck at a 4,s cm target zone located 89 cm away.

The elbow angle, which started at 90°, was required to end at an approximate angle of

120" in order for the target to be hit. Average changes in both myo-electric and myo-

temporal characteristics were calculated in blocks of four trials starting from the first

block (trials 1-4) to the second block (trials 8-1 1) etc., for a total of 100 trials in the motor

task. Significant decreases in target error as well as in puck speed (the time elapsed

between puck release and the attainrnent of the target) and movement-time (the time

between onset of movement to puck release), were observed across training blocks.

Ludwig (1952) confirmed the participants' predisposition to a greater use of force

in accomplishing the motor task within the first few trials (i.e. block 1 ) of the leaming

paradigm, as previously seen with Vorro and Hobart (l98la-b). This was outlined by the

elevated values of total integrated and performance integrated (the total iEMG of the

triceps fiom the onset of limb movement to puck release) EMG activity during execution

of the task. Following this initial period, however. the participants learned to distribute

the forces appropriately as they decreased both the time to peak amplitude of the mucsles

and the latency o f the triceps (an agonist) with respect to the onset of movement. As a

result, there were no meaningfül alterations in the magnitude of the triceps or biceps from

block 2 and on.

Engelhorn (1983)' who suggested that the prevailing kinematic features of the

motor tasks used in the preceding studies had an effect of camouflaging the actual

adaptations in the EMG responses proposed a different methodology. He employed

relatively simple tasks whose kinematic patterns would be rninimized with practice. Each

of these entailed an elbow flexion through a 60' angle fiom an initial joint position of

140". One task consisted of stopping at a point of coincidence with a separate stimulus

visible on an oscilloscope (i.e. a positioning task) while the other involved moving

through the coincidence point within a specified time (coincidence task). Both tasks were

executed at 40" and 200" per second. The EMG data were integrated over six time

periods, two before and four following the onset of movement, in 64 msec bins.

Significant reductions in both movernent time and angular displacernent errors

were found arnong participants after 120 trials of each of the motor skills. An analysis of

the discrete periods of both of the muscle activity patterns revealed that antagonistic

activity in the triceps increased in those time periods wherein adaptive decreases in the

agonist activity of the biceps did not occur, for both the slow and fast movements.

Therefore an augmented CO-contraction in the specific phases of the motor responses was

found to characterize learning.

Contrary to the reports already discussed, McGrain (1986) found no significant

alterations in either the total movement tirne or the myo-temporal variables of a pair of

agonist muscles selected for the analysis of two different strategies of a novel rnotor task.

Seated in a height-adjustable chair, participants used a knee extension rnovement

including the right foot to propel a four-wheel carriage (2,5 kgs) through a timing gate,

located 8 feet away, at 5 mph. Each of two expenmental groups was appropriated either a

back-swing or no back-swing condition of movernent. Although there were changes

between groups, with the back-swing group possessing greater movement times and

increased latencies of the vastus medialis and lateralis muscles by virtue of the reversa1

involved in the task, there were no differences in any of the variables across twenty

practice t d s within each group. These results provided evidence of an experimental task

that was easily acquired without changes in total movement time or timing of the musdes

involved in the activity. According to the investigator, the participants were able to begin

practice of the movements with a motor program, which already met the fundamental

myo-temporal requirements of the task. It was suggested that some other variable such as

the amplitude of EMG activity was manipulated to achieve the criterion velocity of the

motor task.

It is quite evident however, as shown by Gottlieb et al., (1988) that an entire range

of movement compiexity c m elicit significant improvements in critenon learning

variables, including the most seemingly farniliar single-joint tasks. For instance.

participants in the aforementioned study practised both fast and accurate eIbow flexions

of 54" to a target 3" wide within ten separate experimental sessions, conducted on

following days, at 200 trials per session. Researchers observed more than simple

réductions in movement time and increases in the total integrated activity of the biceps

and triceps muscles responsible for accelerating and decelerating the forearm

respectively. They also found that training at one distance increased the propensity with

which they could perform both speedily and accurately at other distances (e-g. a t 36" and

72" movements).

Maring (1990) also found that the mental rehearsai of a simple ball tossing routine

was effective in increasing the rate at which the task was acquired. According to the

elbow flexion movement involved in propelling a ping-pong ball to a horizontal 'bull's

eye' target at a distance of 150 cm, members of an expenmental group were directed to

visualize and 'feel' the movement before they actually performed 10 testing trials.

Following five separate periods of the aforementioned procedure, they had reduced their

tossing error to a significantly greater extent at each stage of the learning schedule as

compared to a control group that did not rehearse. Furthemore, in contrat to the control

group who demonstrated no change in selected myo-temporal variables, expenmen t al

participants had decreased the time to peak activity in both agonist (biceps brachii) and

antagonist (long and lateral heads of the triceps brachii) muscles. An increased latency

between the opposing muscles also chracterized learning that was enhanced by mental

practice.

More recent research by Corcos et al., (1993) extended the work of Gottlieb et al..

(1988) by investigating both within and between session adaptations of 1400 targeted

elbow flexion movements (identical to those described in the latter study) over seven

expenmental periods of 200 trials each. With one day intervening behveen sessions. the

investigators could compare changes in myo-electnc and mechanical variables as a

function of practice (at the end of the B n t session) and learning (across the remaining

sessions). Significant increases in peak velocity, peak acceleration and deceleration

profiles, as well as decreases in the terminal position errors of the movement were found

within the first session. These changes were smaller but similar to those observed and

augmented across sessions. EMG adaptations to the learning paradigrn were consistent

with increases in the intensity of agonist muscle activation in response to an increase in

movernent speed. However, the activation of the antagonist was contingent upon

individual performances as some participants demonstrated a decreased latency of the

muscle (with respect to the onset of the agonist) with learning while others exhibited an

opposite effect. In one particular case, the learner activated the antagonist earlier over

bIocks of the first session and later, across sessions on succeeding days.

Another salient feature of the experiment was the demonstration of retention in

the performance enhancement changes observed with practice fiom one experimental

session to the next. Specifically, performance in the first block of trials conceming the

second session had begun close to but just below the peak attained in the preceding

session and above the level to which performance had declined at the completion of

practice on that first day. Therefore, it was the contention of the authors that the

irnprovements in motor behavior seen with practice, the retention of those improvements

across sessions of the practice paradigm and the reduction in the variability of the

participants responses, which unequivocally defined learning.

A final testament to the above view, on what constitutes learning, was revealed in

the data of the transfer expenments of Jaric et al., (1993). These testing penods were

incorporated into the learning schedule of Corcos et al., (1993), the results of which

expanded on the premise of generalizing the learning at one distance to enhanced

performance at several distances, originally presented in Gottlieb et al., (1988). Pre-test

trials consisted of 11 movements at 18", 34", 54", 72" and 90°, followed by the 1400

trials of the practice schedule and a post-test condition that was identicai to the pte-test

session. Of the five participants studied, three exhibited positive transfer at al1 distances

whereas a fourth only demonstrated transfer to the two longer distances (72" and 90").

Complex Movements

The appearance of a triphasic pattern in fast complex arm movements has been

observed for antagonistic muscles pain at both the shoulder and elbow joints (Wadman.

Van der Gon & Derkson, 1980; Smeets, Erkelens & Van der Gon, 1990). Wadman et al.,

( 1980) found that the triple-burst pattem characterized the activities of opposing muscles

involved at an articulation which exhibited most of the action in accelerated reachinç

movements. When present in both pairs of muscles at each of the joints. the patterns

developed more or less synchronously. Smeets et al., (1990) showed similar results with

flexion movements in which the moments (torques) occumng at the shoulder and elbow

joints of a force in the direction of motion were equivalent. The €MG patterns

demonstrated approximately the sarne timing and intensity for the reciprocal pain of

shoulder and elbow muscles studied.

Altematively, in the execution of fast straight lines and geometric figures with an

electnc pen on an interactive tablet, Accornero et al., (1984) observed a biphasic EMG

pattern in antagonistic muscles of the shoulder and elbow. Although, at times. the

electrical activity in the agonist muscles presented two bursts, the researchers suggested

that a basic building block of one volley in the agonist and one in the antagonist

subserved the various patterns of two-joint ballistic a m movements. These results were

corroborated in an ensuing study by Berardelli et al., (1986) for normal participants

1 O4

perfoming the same drawings of geometric figures in comparison to patients with

Parkinson's disease. The latter group tended to show compensatory multiple bursts in the

agonist for the same actions.

In order to investigate the effects of leaming on both the timing and sequence of

muscle activations underlying a bi-articular motor task, Normand et al., (1982) employed

an experimental protocol of eight separate training sessions, at 100 trials per session, of a

maximum speed horizontal arm adduction, forearm flexion movement. A control group

participated in the pre-test and post-test sessions of the experimental penod each of

which consisted o f five trials. Learners succeeded in reducing their total movement time

for the task as weIl as the movernent times of each of the proximal and distal segment

motions, evaluated separately, in comparison to control group members who were only

found to decrease the time of elbow flexion. Similar to the control group however.

participants trained in the task did not dispiay modifications in the duration o f any of the

agonist or antagonist bursts studied, prompting the researchers to intimate a pre-

programming of the task's myo-temporal features. Instead the individuals learned to

increase the latency between the antagonistic muscles at each joint to allow for the

unimpeded progress o f each of the two limbs during the motor task, for maximum speed.

In a rnotor learning study by Vardaxis (1996), to which the current research is an

addition, a four-day training period of 60 trials per day was utilized to exploit both within

and between session adaptations in the kinematic and myo-eIectric characteristics of two

tasks. They included a uni-directional whipping movement, also used in the present study

(simple task), as well as a bi-directional movement that entailed a reversal at the target of

the latter task, back to the original starting position (complex task).

Significant decreases in performance time were observed for both tasks, within

and between sessions of the experimental protocol commensurate with srnoother and

more consistent end-point, curvilinear, trajectories. Increases in the shoulder and elbow

joint angular velocities were also seen across sessions along with a compensatory

synchronization between the two joints in the complex task. Both amplitude and phasic

modulations in EMG activity were found in the first and second to third wavefoms of the

SVD analysis respectively. They defined a greater activation of agonist and antagonist

muscies as well as an incrrase in the synergistic activation within muscle groups

concomitant with a decrease in antagonistic CO-contraction to enhance the control of both

elbow and shoulder joints, for the two tasks. Furthemore, a partial retention of the

adaptations acquired with motor task practice was also noted for each of the motor skills,

from one expenmental session to the next, which reinforced the efficacy o f the learning

protocol.

In addition to the works presented above, there are numerous investigations

pertaining to the EMG activity associated with multi-joint arm movements primarily

involving reaching andior pointing tasks. Some of these have studied the relationships

between the magnitude and timing characteristics of neuronal activity in the motor cortex

and muscle activations of arm movements in a two-dimensional work space in monkeys

(Caminiti. Johnson & Urbano, 1990; Turner, Owens & Anderson, 1995). Other

researchers investigated path constraints and load perturbations on EMG activity in both

point to point and targeted human arm movements (Lacquanti, Soechting & Terzuolo,

1986; Soechting 1988). Recent work has included a delineation of the basic features

inherent in the EMG pattern for two-joint reaching movements and dynamic isometric

forces in various directions (Flanders, 199 1 ; Flanders & Hermann, 1992; Flanders.

Pellegrin & Geisler, 1996; Pellegrin & Flanders, 1996). Still other studies have sought to

promulgate certain rules or strategies of the CNS conceming the initiation, timing and

magnitude of EMG activity for planar two-joint arm movements (Karst & Hasan. 199 1 a-

b; Gabriel. 1995).

-4tthough al1 of the above studies are revealing in their inquiries into the

phenomenological neurobiology of complex movements, which are central towards an

understanding of how the CNS programs human motor behavior, the motor tasks

involved are fundamentally different from the whipping rnovement being explored in this

investigation. To reiterate, they promote pointing and reaching actions which create more

straight line paths of movement as opposed to the curved trajectory inherent in the motor

task of the present study. Also, a maximum speed condition, employed to elicit the

greatest possible learning adaptations in the currently investigated movement, was not a

necessary circumstance in the tasks of the above research.

Motor Ski11 Retention

The phenornenon of motor ski11 retention has been a focus of inquiry among

investigators across various scientific disciplines. Early studies in ~xperimenral

psychology, which provide an historical perspective on the topic, ernployed pursuit rotor

skills (Bell, 1950; Jahnke, 1958) and other compensatory tracking tasks (Arnmons et al..

1958; Fleishman & Parker, 1962; Harnrnerton, 1963) to assess the effects of interpolated

pauses. or rest periods of no-practice, on motor ski11 training and/or acquisition.

Bell (1 950) utilized a relatively brief practice paradigm of 20 one-minute trials on

a simple pursuit rotor task. Compared to the participants' level of learning on their last

pre-pause test trial, he found that within the first training trial of a retention test one year

Iater. they had only experienced a 29% decrease in their performance scores. Moreover.

any decrements in their motor responses were completely recovered at the end of eight

post-test trials of the motor task.

Jahnke (1958) trained his volunteers at 1, 2.5, 5 or 10 minutes on a similar rotary

pursuit task and re-evaluated their performance at 10 min., 1 day or 1 week post-training.

He uncovered a positive correlation between the initial post-test results and the arnount of

practice received but no statistically determinant changes with respect to the imposed rest

periods.

Arnmons et al., (1 958) investigated participants in a more complex 'Air plane

control test' whose aim was to adjust the orientation of a focal object (a mode1 plane) to a

straight 1 ine position, against various perturbing movements of the latter, using both hand

(control stick) and foot (pedals) controls. Individuals trained for 1, 8 or 40 hours in the

task and were re-tested at 1 day, lmonth, 6 months, 1 year and 2 years later. Larger

decrements in performance were revealed with increasing no-practice intervals, while

those learners who had practised less, experienced a proportionately greater decrease in

task proficiency. Re-learning, which was also studied, required more practice time the

longer the pause without training and the greater the arnount of practice before the

imposed 'rest' interval in question.

Fleishman and Parker (1962) presented differing results on a similar 'aircrafi

control' type tracking task, involving a control stick and rudder pedals to mediate the

fluctations of a target dot and centralize its position on a cathode ray oscillograph. By

increasing the initial training penod to 17 sessions of 21 one-minute trials per session,

distributed over six weeks of pract ice, the experimenters observed nominal performance

decrements in no-practice intervals of up to 24 months. Any srnall losses which did occur

were quickly recuperated within the first few minutes of retraining. Thus the level of

proficiency in the motor skill was observed to be highly dependent on the amount of an

individuals initial training in the task.

Hammerton (1963) debated the difficulty level of the velocity and positional

controls in the compensatory tracking tasks used by previous researchers to describe their

findings, as well as the degree of leaming afforded the participants, which he quatified as

overlearning. To this end, he used a more challenging second-order (acceleration) control

task and two groups differentiated by a level of overleaming in one of them. The

esperirnental task entailed moving a target dot on a cathode ray tube to a target Iine 22,5

mm away and keeping it within a 1,s-mm zone on either side of the line for 2 seconds.

Acceleration of the dot was proportional to the deflection of a thumb joystick. Volunteers

in the regular practice group trained from 40 to 110 trials in the task. while the

overleaming group practised from 90 to 170 trials. Each of these groups was re-tested at

26 weeks post-training. The results indicate decrements in performance as a result of the

no-practice interval, irrespective of the l e d n g schedule but that overlearning did

improve recall of the task.

To clarify the issue of overlearning and its effects on motor ski11 retention,

Melnick (1971) studied groups of individuals who practised a balancing ski11 on a

stabilometer and then received 0, 50, 100 or 200% of extra practice following the

Iearning criterion. At both 1 week and 1 month post-learning, immediate absolute recall

of the gross motor skill was significantly better in al1 of the overlearning conditions as

compared to the performances of participants who did not receive estra practice.

However, when the latter group were given tirne to relearn the task, their scores were

found to differ only with the 200% overlearning group and only at the one-month

retention interval.

In erercise physioIogy research, the terni 'detraining' is used to refer to the

transient and reversible nature of training-induced adaptations (McArdle. 1995).

Attempts to analyze changes. using EMG, in neuromuscular performance within strength

training/detraining paradigms have focussed on both unilateral and bilateral leg

movements and the abstention of the knee extensor/flexor muscles from a strength

training stimulus (Hakkinen & Komi, 1983; Hakkinen, Alen & Komi, 1985; Narici et al..

1989; Hortobagyi et al., 1993). Depending on an individual's distribution of motor units

within a muscle (or muscles) and his or her capability of controlling the gradation of

muscular force through such mechanisms as recruitment ancUor rate coding, for instance,

i t is possible to think of maximum strength as a motor ski11 (Vandervoort, 1992).

Preliminary research by Hakkinen and Komi (1983) included participants

accustomed to weighi training who followed a progressive resistance strength-training

program of 16-weeks duration. It combined both concentric (75% of contractions studied.

at 80-100°/b of one maximum concentric repetition. 1-6 reps per set) and eccentric (25%

of contractions, at 100-120% of one maximum concentric repetition, 1-2 reps per set)

contractions using a dynamic squat lifi exercise. An eight week detraining penod ensued

wherein al1 strength training was teminated. A significant increase in the maximal

bilateral isornetric force of the quadriceps was found post-training, concomitant with a

similar augmentation in the averaged maximum integrated EMG (IEMG) activity of the

leg extensor muscles (Le. rectus femoris, vastus lateralis and medialis), up to 12 weeks of

the training regimen. Both the isometric force and IEMG measures were observed to

decrease after detraining but not to pre-training levels. The authors attributed the decline

in neuromuscular performance to an absence of the strength training stimulus and

categorized the detraining effect as 'comparable to the opposite effects of training'.

In a secondary investigation, Hakkinen and Komi (1985) extended both the

training and detraining penods to 24 and 12 weeks respectively, along with increasing the

nurnber of repetitions for each of the concentnc (1-10) and eccentnc (3-5) contraction

exercises, described above for the sarne squatting exercise. Similar decrements in the

averaged maximum IEMG values of the quadriceps muscle group, frorn post-training

leveIs, were observed after detraining which correlated significantly with the decrease in

maximal isometric force for the sarne no-training penod. However, an improvement in

the maximal rate of isometric force production, particularly at the higher force levels

analyzed (e-g. 3000 N), was found to persist or even be further enhanced dunng the

detraining period. These results led the researchers to suggest an ongoing adaptation of

the motor unit recruitment pattern subserving fast force production in experimental

participants, despite a termination of the training program.

Experiments by Narici et al., (1989) incorporated isokinetic knee extension

training (at an angular velocity of 2.09 radlsec) of the dominant leg in participants. who

were exercised for six series of ten maximal contractions, four times a week for fifieen

weeks; they subsequently detrained for the following ten weeks. The results at the end of

training revealed an increase in the cross sectional area of the quadriceps that was only

approximately iess than half of the rise in the maximal isometric force production (MVC)

of the trained leg. The changes in force output in hm, were only about half of the

increase observed in the IEMG activity of the vastus lateralis indicating that the

enhancement in MVC with training may have been influenced by a greater neural

activation as opposed to an increase in muscle hypertrophy. Moreover, the authors

suggested that increases in both IEMG and MVC measures for the untrained kg,

although not statistically significant, alluded to a supraspinal modulation of the neural

drive to the muscles. The kinetics of the changes seen in each of the above-mentioned

variables with leaming, were observed to have an equal time-course during detraining.

Ishida, Moritani and Ito, (1990) studied the relationship between modifications in

maximal voluntary strength and selected twitch contraction parameters evoked by

electrical stimulation, in an attempt to elucidate the central andlor peripheral factors

mediating the adaptations during both training and detraining. Volunteers were trained in

a heeI raising exercise whose program consisted of three sets of 15 repetitions per set

(using 70% of the maximal load on day 1) three times a week for eight weeks. They

demonstrated a significant rise in the MVC of the gastrocnemius muscle with training, in

comparison to no particular changes in the maximal twitch torque or maximal rate of

torque development in the triceps surae muscle. In contrast, eight weeks of detraining.

which resulted in no apparent decrease in MVC revealed a significant increase in the

maximum value conceming the rate of torque production. The investigators speculated

that central factors contributing to the augmentations in the maximal strength of trained

muscles might facilitate a potential for complex post-detraining adaptations in the same

muscles afler training has ceased.

Staron et al., (1991) showed similar results of a propensity for individuais to

retain strength-induced adaptations during a detraining period but what made their

findings unique was the fact that the no-training interval was extended to 32 weeks.

Specifically, women who had subscribed to a 20-week progressive resistance strength

training program, including dynamic squat, leg press and leg extension exercises.

continued to demonstrate maximal performances for the squat at eight months post-

detraining that had not significantly diminished fiom post-training measures. The values

for the other two exercises exhibited statistically defined decreases at the end of

detraining but not to pre-training levels. To assist in the evaluation of these data the

researchers noted a sustained hypertrophy of the myofibers within muscle biopsies of the

women's vastus lateralis and also suggested a retention of neural adaptations as a resuIt

of training. According to the authors, it was the acquired reserve of each of the

aforernentioned factors that decidedly aided the previously trained women in additional

re-training experiments (Le. 6 weeks), versus a second group of untrained women.

achieve maximal strength increases in each of the exercises within a comparatively

shorter time.

Hortobagyi et al., (1993) further underscored the importance of an individual's

training status as a determinant factor in the assessrnent of detraining effects on acquired

muscu1a.r strength levels, particularly among power athletes who are characterized by a

long history of strength training. To this end, the investigators studied a group of strength

ath letes, composed of power li fiers and football players, homogeneous in anthropometric

characteristics and who possessed similar weight lifting performances and workout

schedules. They were evaluated on a series of maximal strength measures including both

isometric and isokinetic knee extension/flexion forces, as well as one repetition

maximum testing of free-weight bench press and squat exercises both before and after a

14 day detraining period. An analysis of pre- and post-detraining measures revealed

statistically significant decreases in only maximal eccentric knee extension strength

performed at angular velocities of 0.87, 2.62 and 4.37 radsec. An EMG analysis of the

vastus lateralis during each of the aforementioned testing conditions could not explain the

decrements in eccentric strength since there were statistically insigni ficant reductions in

the muscle's activity level, suggesting maintenance of the neural drive to the latter.

Instead, the investigators indicated a probable decrease in the hypertrophy of fast twitch

muscle fibers associated with eccentric strength gains. Thus when the initial training level

of an athlete is very hi& short-term detraining periods do not necessarily have any

deleterious effects on the specific adaptations in maximal concentric forces developed

with long-term strength training.

The consequences of reduced training periods on neuromuscular performance

have also been evaluated for both previously trained and untrained individuals. Research

conducted by Graves et al., (1988) involved two groups of participants (previously

untrained for at teast a year) who had been undergoing variabte resistance, bilateral knee

extension strength training programs for penods of ten and eighteen weeks. Individuals

who were trained two days a week and three days a week in both of the training regimes

experienced significant increases in maximal bilateral isometric strength as well as in the

amount of resistance used during training. All of these people were subsequently engaged

in twelve weeks of reduced training fiequency. Those who had trained at 2 days per week

were randomly assigned to both a 1 day a week group and a detraining group while

rnembers who exercised for 3 days a week were relegated to a 2 days per week group and

a 1 day a week group. The findings demonstrated no statistically significant reductions in

either of the above mentioned strength measures for those groups in which training had

been reduced to 2 days a week and 1 day per week. The detraining group, on the other

hand. exhibited a decrease of more than half of their original post-training isometric

strength.

Hakkinen et al., (1991) investigated reduced training in ten strength athletes

composed of power lifters and body builders, each of whom possessed a systematic

strength training background of 5 to 10 years. Al1 of the athletes participated in a three-

week experimental period incorporating a two-week 'regular* heavy resistance strength

training program for the leg extensor muscles followed by a one week period in which

the overalI volume of training was reduced by 50%. The regular program consisted of a

squat-lifi exercise of 18-22 contractions per session at 70%-100% of one maximum

repetition (1RM) and a leg press or knee extension exercise of 20 to 40 contractions per

session at 60%-80% of IRM, every second day. The results showed no changes arnong

the athIetes in bilateral MVC dunng leg extension, maximal force per cross sectional area

(force/CSA) of the quadriceps (each of which were found to be comelated), and maximal

averaged IEMG of the vastus lateralis, medialis and rectus femoris, before and afier the

three-week period. The researchers found, however, that they could divide the group into

five 'best' athletes and fwe 'other' athletes based on a person's value of maximal

force/CSA of the quadriceps. This distinction between the two groups revealed that the

'best' athletes exhibited significant increases in both bilateral MVC and averaged IEMG

during the reduced training period as opposed to the 'others' who did not. The

investigators concluded that in the case of highly trained strength athletes, who may have

at~ained their maximum in neuromuscular performance. fùrther improvements in

maximal strength ancUor neural activation may be accrued not fiom 'normal' training

periods but rather fiom a short penod of 'reduced' training.

As was presented within section 1.2 of the introduction, a separate experimental

mode1 based on the spinal stretch r e m (SSR) has aided in defining the underlying

processes andlor substrates accounting for the acquisition and sustenance of a simple

motor ski Il (Wolpaw, 1994). The learning paradigm involved training monkeys to

maintain a constant elbow angle (90°) against an extension torque for a pre-specified time

interval. If the averaged EMG activity of the focal biceps was found to be in a certain

range. a small additional extension torque would be provided to extend the eIbow and

elicit the biceps SSR. Liquid reward was given to the monkeys 200 msec aller the extra

torque. The animals were trained under one of three different modes, a control mode, in

which the reward always followed the additional torque, established the base-line

amplitude of the response. Converseiy, under each of an SSR-up or SSR-down mode.

reward was only given if EMG activity was greater (SSR-up) or less (SSR-down) than

the control value.

Leaming in either of the two experimental modes, characterized by 3,000 to

6,000 trials per day over a period of 2 to 17 months, elicited a different learning cuwe

than that seen in traditional motor learning paradigms. An immediate change of

approximately 8% in the specific direction of a mode was observed on the first day of

training, which preceded that modes gradua1 development over weeks, in which 80%-

90% of the change actually occurred (Wolpaw, Braitman & Segal, 1983; Wolpaw &

O'Keefe, 1984). lnvestigators suggested that the initial phase development process

entailed an operant conditioning of one or more descending spinal cord pathways acting

on the reflex arc mediating the SSR and that the chronic daily presence of this activity

produced a persistent structural and/or biochemical alteration in the spina1 cord. The fact

that these changes were observed to persist over pauses in training of 10-38 days

supported the notion of an adaptive plasticity in the spinal cord (Wolpaw et al.. 1986).

Further studies on the reversal and redevelopment of SSR change, demonstrated

similar incremental evolutions in the face of opposite mode imposition followed by

reimposition of the original mode (each of which also survived non-performance breaks)

that reinforced the hypothesis of a persistent segmental alteration (Wolpaw, 1983).

Moreover, the predominance of the SSR phenornenon in the focal agonist (biceps) as

compared to other synergistic (brachialis and brachioradialis) and antagonist (triceps)

muscles underscored the feasibility of the SSR system as a substrate for the study of

memory in primates.

Recent motor control research, focussing on the acquisition and retention of

motor skills has investigated complex tasks as well as visual imaging of the brain itself.

in order to elucidate the resulting CNS adaptations to each of the preceding phenornena.

Kami et al., (1995) noted both substantial improvements and significant retention arnong

participants in the learning of a motor task that required the rapid tapping of accurate

finger sequences in opposition to the thumb of the non-dominant hand. A training

schedule incorporating 10 to 20 minutes of practice per day for five weeks resulted in a

performance index that was two times the speed of accurate sequencing exhibited at the

beginning of practice. The performance enhancement displayed a fast early rising phase

within the first w-eek that was followed by a more gradua1 evolution of acquisition to

asymptote by week four. The task showed linle transfer to the other hand and did not

generalize to the execution of a different control sequence of equivalent component

movements. The researchers did find however, that the MW of local blood oxygenation

level-dependent (BOLD) signals elicited in the primary motor cortex (M 1 ) demonstrated

a consistently larger activation area for the trained sequence in cornparison to the control

sequence. The tirne course in the development of the size differences between the trained

and the control sequences of the Ml response corresponded with the maximal asymptote

performance of the trained sequence, suggesting that leaming is charactenzed by a new

and more extensive representation in the motor cortex. Additional retention experiments

reinforced a long lasting effect of the graduai learning process, as a persistence of

superior performance in the task and in the evoked M l response was observed after 10

and 2 1 weeks of no extra training.

In their study, Brashers-Krug et al., (1996) investigated the underiying

consolidation process of an experimental task in motor memory. They trained a total of

seventy individuals in the use of robotic manipulandum to make 10 cm rectilinear

reaching rnovements fiom a central position to eight different target locations, at a

moderate Pace (i-e. 500 msec). An initial target set consisting o f a senes of 192

movements was first used to establish baseline motor response patterns before the

introduction of a second set in which the manipulandum provided perturbing forces in a

clockwise direction. The participants were required to learn to compensate for these

forces in an effort to continue to guide their rnovements to the targets (task 1). The

performance index of learning was the degree to which the participants could adjust to

the extra forces in reproducing their baseline trajectories

The investigators found that a control group tested 24 hours after the learning of

task 1, exhibited a significant irnprovement in their performance with respect to post-

training values. An experimental group, which received training in a different pattern of

forces (conter clockwise) immediately after the learning of task 1, demonstrated a

reduced learning capacity or negative transfer in the second task. When tested a day iater

for retention of the first task, the performance level of the experimental group was

comparable to the index of learning observed after training but it did not show any

additional improvement, as had been noted for the control group. Therefore the extra

training in task 2 apparently compromised the retention of the first task (retrograde

interference). Intervening with the second task at 5 minutes, 1 hour and four hours post-

training, in three other separate groups revealed that only the 4-hour group could display

a statistically significant increase in the retention of task 1. However, both negative

transfer and retrograde interference were seen to decrease monotonically with increasing

no-training intervals. According to the researchers, there would thus exist a small time

time-window in hurnan motor memory wherein a more fragile representation of memory

is stored before it is transformed or consolidated into a more solid state.

In a follow-up study, Shadmer and Brashers-hg (1996) trained another group of

volunteers in a longer practice paradigrn of three target sets for each of the two different

tasks described above, that were separated by a 24-hour interval between training

sessions. Significant improvements in perfomance were observed at two and three weeks

beyond the completion of training for tasks one and two respectively while a control

group, which was only trained in first task, continued to show a high level of leaming at 5

months afler the initial practice session. Two separate intemal models of motor action

had therefore been consolidated in long-term motor memory when the temporal distance

between the learning of two independent skills was 24 hrs. The investigators also re-

evaluated the time course in the consolidation of the motor skills based on the newly

protracted practice period (to ensure a learning plateau) and a recall session that was

extended to 1 week post-training instead of 24 hours (employed to nulliS, any effects the

leaming of task 2 might have had on the subsequent recall of task 1 - anterograde

interference). They found a significant recall of the first task at 5,5 hours following the

completion of training in task 2 but that the retention level approached the performance

index of the control group only at 24 hn post-learning.

In yet another study, Shadmer and Holcomb (1997) provided evidence of a

reorganization of the neural representation of human motor memory to support the

îïndings of Brashers-Krug et al., (1996) and Shadrner and Brasher-Kmg, (1996)

regarding the stability of the intemal mode1 of a motor task, aHer only a few hours

following acquisition. The authors procured positron emission tomography (PET) scans

of the brain as participants leamed the task of a novel mechanical system (identical to

that used in the previous studies). Measures of regional central blood flow (rCBF) were

correlated with total motor output over areas of the prefrontal cortex dunng training of

the task. Participants were then monitored a second time at 5,s hours post-learning. a

period that signified consolidation of the motor ski11 in the above research. The

investigators observed new regions where activations correlated significantly with motor

output, the premotor, posterior parietal and cerebeller cortex, concomitant with a

reduction in the preceding correlation for the prefiontal areas.

Appeadix 2

QUESTIONNAIRE

Age :

Height: m Weight: kgs

Arm preference: please pnnt a response of either "Lefi" or "Right" for each of the

questions below, in the spaces provided.

1) Which hand do you employ when writing?

7) M i c h hand do you ernploy when grasping the handle of a racquet (i.e.

badminton, squash, tennis) or tooi such as a harnmer?

3) Which side do you use when holding and stnking with a baseball bat?

4) Which hand do you use when throwing a baseball or softball?

5) Which hand is used when pitching underarm in softball?

6) Which hand is employed when striking a punching bag for power?

George Sarantinos .M.A. Candidate McGill University Department of Physical Education 475 Pine Ave. West Montreal, Quebec, H2 W l S4

Appendix 3

Dear:

Your interest regarding participation in this study is very welcomed and much appreciated. The purpose of this experiment is to inquire into the electromyographic changes in and between selected muscles of the lefl upper limb and chest following both training and afier periods of no practice.

There will be a total of nine testing sessions to occur in the exercise physiology laboratory of McGi11 University's Seagram's Sport Science Centre. The first of these sessions will entail the measurement of your height and weight, and include the completion of a questionnaire to determine right arm/hand preference. For your own comfort and to facilitate the testing protocol, you will be asked to dress in shortdlight pants and a t-shirt.

Prior to actual data collection, you will be placed in the chair of an experimental table using velcro straps to lirnit movement of the waist and upper torso. A plastic apparatus will be secured to the top of your forearm using velcro straps once again, as well as athletic tape. Six adhesive surface EMG electrodes will be placed on six sites of your left upper limb and chest. These are the back of each of the shoulder and upper a m , the left side of the chest below the collar bone, the front of the upper arm and above the forearm. The EMG electrodes will provide information concerning the attendant eIectricaI activity of each of the muscles under study during both training and no-practice. In order to optimize conductivity at the electrodelskin interface sites, shaving of local surface hair will be required. Furthemore, each of the six sites will be outlined using a non-toxic permanent ink marker to ensure the sarne electrode placement for each testing session.

Subsequently, you will be asked to perfonn (3) three sets of twenty-five (25) trials of an unrestrained movement using the left ami in the horizontal plane. The task will need to be performed as quickly as possible, beginning from a 'home' and terminating at an end 'target' position. You will repeat the protocol of the motor task for four (4) consecutive days (including the first) and then return to the lab for one set of ten trials of the task one day afier the training period and at 1, 2, 4, 6, and 8 weeks post-training. During this time you will be requested to refrain tiom any type of strength training involving the upper body as this may influence your testing performance.

By the end of the training period you may experience some soreness of the biceps muscle due to the nature of the task. The use of EMG electrodes to record the electrical activity of the six muscles assumes no nsk.

118

You can be assured that a11 persona1 and data coIIected will be held in the strictest of confidence by the experimenter. Your files will be numerically encoded so as not to reveal your tme identity at any time; neither during the testing sessions nor in the final paper.

Via this experiment significant knowledge will be gained conceming neuromuscular hc t ioning when sufficiently trained and pnmarily how abstaining fiom practice may affect either an athlete's or even a non-athIete's neuromuscular performance. If you decide to proceed as a participant, you will have the unwaivering option of withdrawing fiom this investigation at any time and request to have al1 persona1 information and data destroyed. No reasons need be given, no questions will be asked.

1 thank you and welcome any inquiries you rnay have.

Sincerely,

George Sarantinos, M A . Candidate

Appendix 4

Informed Consent Form

1 , g a n t permission to George Sarantinos

to proceed with:

1. The measurement o f Anthropometric components (Height and Weight).

7 -. The placement o f surface adhesive EMG electrodes to record the myoelectric activity of six (6) muscles of the left upper limb and chest.

3 . The collection o f 450 trials of data of a 'fast' two-joint motor task, during both training and retention conditions for the purpose of investigating the "Learning and Retention Adaptations of Myoelectric Activity During a Novel Multi-Joint Task".

1 have read and clearly understood an explanation o f the nature, procedures, purposes, risks and benefits of the proposed research in which 1 will be participating. 1 am fully aware that this research project is investigational, that 1 am at liberty to withdraw from the study at my own discretion, at any time, by simply asking to do so and request to have al1 persona1 information and data files destroyed. With this in mind and having clarïfied any further persona1 inquiries with the investigator, I voluntarily consent to the methods/procedures enumerated above.

Signature:

Witness :

CERTlFlCATE OF ETHICAL ACCEP INVOtVlNG HUMAN

tABtLlW FOR RESEARCH SUBJECTS

A review cornmittee consistirtg of thma cf the follcwing membem:

1. P d . E. t u a thaue . 1. Prof. M. Maguire

2 . Prof. R. Ghorh 2. Prof. N. Jeckson

3. Frof. M. Downey 3. Prof. H. Pemault

has examined the application for certification of the etkical acceptabilay of the projec! titled:

The Ef fecrs of Detraining au Neuromscular I h i l t i - joint Coordiaaciou. -

The review cornmittee considers the researcn procedures. as explained by the appllcant in this application, to be acceptable an ethical grounds.

L- (Sig ned)

Appendix 6

ANOVA table for Performance Time data - Experimental group

Source Type of test d. f. F P

Learning Within-Subjects Contrasts (1,9) 29.3 1 0.0001

Retention Within-Subjects Conri-asts

Day 5 vs. Ret 1 (1 ,9) 0.22 0.639 Ret 1 vs. Ret 2 (1 ,9) 10.35 0.01 1 Ret 2 vs. Ret 3 ( L 9 ) 0.53 0.387 Ret 3 vs. Ret 4 ( 1-9) 0.68 0.432 Ret 4 vs. Ret 5 ( 1-9) 0.67 0.433

Appendix 7

ANOVA table for the PerCormance Time differences between the Experimental and Control groups


Learn-Ret Within-Subjects Effects (2,26) 13.416 0.0001

Learn-Ret * Group Within-Subjects Effects ( 2 3 ) 7.252 0.003

Learn-Ret 1 Within-Subjects (Day 1 - Day 5) Contrasts (1,13) 18.195 0.001

Learn-Ret 2 Within-Subjects (Day 5 - Ret 5 ) Contrasts (1,131 8.625 0.01 2

Learn-Ret l*

Group Within-Subjects (Day 1 - Day 5) Contrats W 3 ) 5.749 0.032

Learn-Ret 2* Group Within-Subjects (Day 5 - Ret 5) Contrasts ( 1 , 13) 8.758 0.01 1

Appendix 8

ANOVA table for the composite score data of W2 - Experimental group


Leaming Within-Subjects Contrast (1,9) 35-12 0.0001

Retention Within-Subjects Contrasts

Day 5 vs. Ret 1 Ret 1 vs. Ret 2 Ret 2 vs. Ret 3 Ret 3 vs. Ret 4 Ret 3 vs. Ret 5

Appendix 9

ANOVA table for the Composite Score differences of W2 between the Experimental and Control groups


Learn-Ret Within-Subjects Effects (2-26) 9.39 0.00 1

Leam-Ret * Group Within-Subjects Effects (2-26) 4.289 0.025

Lem-Ret 1 Within-Subjects (Day 1 - Day 5) Contrasts (1,13) 12.165 0.004

Learn-Ret 2 Within-Subjects (Day 5 - Ret 5) Contrasts (1,13) 5.476 0.036

Lem-Ret 1 * Croup Within-Subjects (Day 1 - Day 5) Contrasts (1,13) 0.238 0.634

Learn-Ret 2* Group Within-Subjects (Day 5 - Ret 5) Contrasts (1,13) 10.004 0.007

APPENDICES 10 - 14

The following appendices contain the data of the third waveform (W3) of the

SVD analysis for both the experimental and control group members in each of their

leaming and retention conditions. An attempt was made to organize this data in a rnanner

that would highlight the agonist and antagonist muscles central to the execution of the

motor task as revealed by the eigenvector loadings for each of the muscles studied. To

this end, the names of the relevant agonist andior antagonist muscles for a particular

experimental condition are first provided within an appendix table (A) in their

abbreviated form. The purpose is to provide a visual presentation of the interrelationships

of the muscles in each of the extensor and flexor groups involved in the production of the

motor task and how these relationships change across experirnental conditions.

According to the magnitude and polarity of their respective eigenvector loadings

the muscles are listed in order of decreasing magnitude and as either firing sequentially

(e.g. PD vs. LO) or synchronously (e.g. LO + LA). A second appendix table (B) displays

the actual eigenvector loadings or muscle coefficients which categorize the representat ion

of agonist and antagonist muscles seen in the preceding appendix.

Appendix 10A

Dav 1 Dav 5 Partici~ant:

Pl LO vs. PD . . .LA

Br - -. -Tu .

P2 . > .

LA vs. PD LA.+ U) H> Bic . ' 8 ,

., --. . , . . , , . ..*- .. -

P3 LO vs. PD ,?- ,-a :: , - . . . . , :-. . .

Pec P5 LA \-S. PD PD-vsLA+LO

Bic Bt P6 LA "' 'LA vs. .m.

Bic vs.Pec S. - - . - . .- . . .W. - ,

P7 LA vs. PD Y* '" .mmA L1 '

Bic

-

Pl0 PD vs. LA + LO L A vs. PD Bic Pec \-S. Br + Bic

Within muscle group representations of W3 for the leaming penod (Day 1 to Day 5) of the experimental group. P7 is presented in the bold font. The white and grey areas denote a local and global pattern of the waveform respectively. The muscles are presented in order of decreasing magnitude according to their eigenvector coefficients.

Appendix 10B

Day 1 Dav 5

P3

P4

1 -0.46/-0.31 vs. 0.33 1 0.61 . 1

P7

0.66 vs. -0.5 1

-0.4 0.61 vs. -0.51

Eigenvector coeffkients of the within muscle group representations depicted in Appendix 10A, for the learning period @ay 1 to Day 5) o f the expenmental group. The data for P7 are presented in the bold font. The white and grey areas denote a local and global shape of the waveforms for W3.

-0.55 VS. 0.49/037 I . - A S 4

I

-0.71 vs. 0.65

-0.63 vs.0.40 0.56 vs. -0.32

Pl0

+ - _ -0.57 . J

: ,-,-@!W va^ -46f

-0.70 0.57 VS. -0.39/-0-30 1

-0.53 \-S. 0.33/0.30 0.48 vs. -0.39

Appendix 1 1 A

w Ret 1 Ret 2 Participant:

,_ - - z$;+--~?, *:-':y ::.-:-A - : * ? t.JTp+-z: +:+;;-y :- Pec .- . . ,-. . .- , - . . . - ,.., , . . L - . .-.- ". =,< '.

PS .*vt:;Zb-+. u: - 2 ;- ,PD - ; - mI$&:m -+: 7.. ." , * ~0

I: . ABiC I Pec vs. Bic I Pec vs. Bic T

P6

- .- .

P8 PD VS. LA + LO . PD vs:-LO ,+ Lh PD vs. LO * . B a . . .

r . -. 1 BrR + Bic rs. Pec

BrR LA.--, PD

1 Pec vs. BrR + Bic 1 BrR vs. Bic + Pec 1 BER "

Within muscle group representations of W3 for the short-terni motor memory period (Ret 1 and Ret 2) of the experimental group. Day 5 of the learning period is included for comparative purposes. P7 is presented in the bold font. The white and grey areas denote a local and global pattern of the waveform respectively. The muscles are presented in

order of decreasing magnitude according to their eigenvector coefficients. The asterix (*),

t LO vs. TI *

cross (t) and double cross ($) superscnpts highlight a decrement, persistence or

improvement in motot coordination respective1 y.

129

Bk * LO vs. LA

Appendix 11 B

Da? 5 Ret 1

. . -a54 t 0.37 f P4 -0.71 vs. 0.65 0.51 vs. -0.40

p6 1 O=I2+~.4.33 - 1 -0.52 vs. 0.34 *

P9 1 0f4v&o-31 1 -0.55 \-S. 0.50 -0.45 vs. 0.44

Pl0 0.48 vs. -0.39

1 0.57 vs. -0.39/-0.30 ( -0.77 vs. 0.54/0.31

Ret 2

4.70 vs. 0.64

-0.55 vs . 0.31

0.56 vs. -0.37t

Eigenvector coefficients of the within muscle group representations depicted in Appendix 11A, for the short-tenn motor memory period (Ret 1 and Ret 2) of the expenmental group. Day 5 of the learning period is also included for comparative purposes. P7 is presented in the bold font. The white and grey areas denote a local and global pattern

of the waveform respectively. The asterix (*), cross (t) and double cross ($) highlight a

decrement, persistence or improvement in motor coordination respectively.

Appeodix 12A

Ret 2 Ret 3

1 1 P D vs. LO 1 1. y m.-PDD BrR + Bic vs. Pec :, . -*: mw pe: :..- I

PD U v s . PD $ Pec FS. Br Pec

P6

Within muscle group representations of W3 for the first long-term motor memory condition (Ret 3) of the experimental group. Ret 2, of the short-term motor memory period is also included for comparative purposes. P7 is presented in the bold font. The white and grey areas denote a local and global pattern of the wavefoxm respectively. The muscles are presented

in order of decreasing magnitude according to their eigenvector coefficients. The asterix (*),

cross (7) and double cross ($) superscripts highlight a decrement, penistence or improvement in motor coordination respectively.

LO vs. LA

Pec vs. Bic f 1

LA vs. LO ? Pec vs. Bic

Appendix 12B

Ret 2 Ret 3

P6 1 -0.55 vs. 0.31 1 0.12 rs. -0.36 t

P7

P9 1 0.40 * 1 -0.74 rs. 0.40 $

p8

0.56 \-S. -0.37t

-0.78 vs. 0.55 *

Eigenvector coefficients of the within muscle group representations depicted in in Appendix 12A, for the first long-term motor memory condition (Ret 3) of the experimental group. Ret 2, of the short-term motor rnernory period is also included for comparative purposes. f 7 is presented in the bold font. The white and g e y areas denote a local and global

pattern of the waveform respectively. The asterix (*), cross (t) and double cross ($) highlight

a decrement, persistence or improvement in motor coordination respectively.

0.59 vs. -0.53

&6'9 m. -492 +

-0.52 vs. 0.47 * -0.37/-0.31 vs. 0.43

Pl0

a @SS:VS.' i as+- $7 - 447 4-0.38 - -

0.68 vs. -0.47

'0.65 vr. 451Q171A3 -

0.41

-036 vs. 0-37.033

Appeadix 13A

Ret 3 Ret 4 Ret 5 Panici~ant:

1 Pec vs. Bic 1 Bic + BrR vs. Pec

PD vs. LA

- - .BIRs . .-*.,.l I * . . . - - BrR vs. Bic

Pl0

Within muscle group representations of W3 for the second and third long-term motor rnemory conditions (Ret 4 and Ret 5) of the experimental group. Ret 3 is also included for comparative purposes. P7 is presented in the bold font. The white and grey areas denote a local and global pattern of the waveform respectively. The muscles are presented in order of

decreasing magnitude according to their eigenvector coefficients. The asterix (*), cross (P) and double cross ($) superscnpts highlight a decrement, persistence or improvement in motor coordination respectively.

133

Pec

P D v s . U + L O Bic + BA vs. ~ e c

LO $

Bic t PDvs.LO +LA

Appendix 13B

Ret 3 Ret 4 Ret 5 Partici~ant:

4.e~. 038 -- -0.44/-0.40 * -0.58/-031or; a37 - -+ ,

- . - . - P9 -0.74 vs . 0.10 $ -:@4-vr 431- * 0.67 +&&3/-0:~i

. . <

- . -- g r . .

. . - 0.41 rs~;@/ia~~ii;-.. . - ..

r . . , . , . . . . ... pl0 . . - .0a7~0.&! . 0.38 $ - 0;68.vs.-û.54/-0;34

0.59 vs. -0.54

0-9-W. OS, . .* -

Eigenvector coefficients of the within muscle group representations depicted in Appendix 13A, for the second and third long-term motor memory conditions (Ret 4 and Ret 5) of the experimental group. Ret 3 is also included for comparative purposes. The data for P7 is presented in the bold font. The white and grey areas denote a local and global pattern

of the waveform respectively. The asterix (*), cross (t) and double cross ($) highlight a

decrement, persistence or improvement in motor coordination respectively.

-0.48/-0.34 vs. 0.30

. 0œ-W:m. * L

Ofi2 . 3 4.@-~.'0.59

Appendix 14A

Dav 1 Dav 5 Ret 5 Partici~ant:

LA + LO vs. PD

Within muscle group adaptations of W3 for Day 1 , Day 5 and Ret 5 conditions of the control group. The white and grey areas denote a local and global pattern of the

the wavefom respectively. The muscles are presented in order of decreasing magnitude

according to their eigenvector coefficients. The asterix (*), cross (t) and double cross ($)

superscripts highlight a decrement, persistence or improvement in motor coordination respectively.

Appendix 148

Eigenvector coefficients of the within muscle group adaptations depicted in Appendix 14A, for the control group conditions @ay 1, Day 5 and Ret 5). The white and grey areas denote

a local and global pattern of the wavefom respectively. The asterix (*), cross (t) and

double cross ($) highlight a decrement, persistence or improvement in motor coordination respectively.

w w Ret 5 Partici~ant:

Cl

C2

C3

C4

C5

-0.47

0.85

0-63vs--0.37

0.12 vs. -0.37/-0.37

-0.39

0.71 YS. -0.47

0.82 vs. -0.35

-0.3 1 -0.71rs.0.49

0.42

-0.50 T

0.73

-0.64-~~.-0-53,l-0.34~-

. - . ,, . 0.4z . f * ,'.y - - - ' - - % 6. - &%/-O& ys. 0~45:

0.62 f 0.78 m. 4.48

.f - ~

~ ; ~ ~ ' ~ j ~ ~ ~ ; 3 4 ~ ' : ~ n , ~ J ~ ~ ' - .,. . . + :<- -'x-..d ,.

- . - - . .

a65 VS. -0.58/-0.30

0.37

-Q17i.%-&@

0.39 * . i 5 2 rr. 0.42 *

0.66 W. -0.33

-0.70.+ OJl "' : 0$.1 . ,

. .

c- -:,

0-42 *

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