dimensions of motor speed - joch

8/17/2019 Dimensions of Motor Speed - Joch

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DIMENSIONS OF MOTOR SPEED

By Prof. Dr. Winfried Joch

An overview of the recent in formation on speed performance factors, including reaction speed, acceleration, stride frequency and stride length in sprinting. Thearticle is based on a condensed translation from Die Lehre der Leichtathletik,VoL 28, No.22, 1989, edited by Helmar Hommel and published by Deutscher Sportverlag, German Federal Republic. Re-printed with permission from modern

Athlete and Coach.

Speed is an essential component in a sporting performance. Speed belongs withstrength, endurance and mobility to the “motor qualities”, or “basic qualities”, or“motor capacities”. In track and field it is normally measured as the time intervalrequired to cover a certain distance - l00m (= distance) in 11.0 sec. (time

interval). Next to the usual sporting concept of speed, there is the concept of velocity. Velocity (v) is defined as the relationship between the covered distance(s) and the time (t) required for it. The formula is:

___s___ V =

t

For example, Ben Johnson in the Seoul Olympic final reached in the 9.79 sec.between 50 and 60m in 12.04m / sec., his highest velocity. Carl Lewis in thesame race was in 9.92 sec. 0.13 sec. slower, yet his maximal velocity, achievedbetween 50 and 60m, was in 12.04m/sec., equal to Johnson’s.

Velocity applies to both cyclic and acyclic movements. Cyclic movements aredenoted as movements with repetitive part-phases, such as walking, running,swimming and rowing. Acyclic movements are such movement patterns wherepart-phases are not repeated, such as throwing and jumping.

Speed can be divided into three relatively independent areas (dimensions):reaction, acceleration, frequency. (Fig. 1).

REACTION

Three different stimulants, responsible for different reaction times, can bedistinguished in the reaction speed. The human reacts the fastest to a touchingstimulus. The time is given as 0.10-0.18 sec. The reaction time to acousticsignals ranges between 0.12 - 0.18 sec. and to optical signals between 0.15 -0.18 sec.


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Figure 1: ORGANIZATION OF THE SPEED DIMENSIONS

It should be taken into consideration that these figures differ considerablyaccording to the measuring methods of the reaction time or the apparatus(reaction meter). This physiological law is used to set 0.10 sec. as the lowestlevel of the reaction performance and times below 0.10 sec. are considered as“anticipated”.

The different reaction performances — touch, acoustic and optic — are specific.This means that the one who reacts very fast to an optical signal, can reactslower to an acoustic signal and vice versa. This, for example, is important inrelays, where the first runner, as in sprint races, reacts to an acoustic signal, all

others however to a visual signal.

There is a basic difference between simple reactions and choice reactions.Simple reactions are based on the performance of a previously definedmovement (in sprinting, the starting action) following a known signal (the starter’sgun). A choice reaction ( in the simplest format), for example, takes place in thereaction to an optical signal when a green button has to be pushed when a greenlight appears and a red button on the red signal.

According to Zaciorskij there are five stages in the reaction processes from thesignal to the first muscular activity. However, it is sufficient in sporting activities to

define reaction time as the time taken from the signal to the first muscular action(reaction time including the latent time).

It is presumed that the reaction time, at least in the sprint start, can be improvedthrough the pre-tension of the muscles (pressure on the blocks in the “set”position), as well as the previously warmed up musculature. This is even moreprobable when the number of muscles participating in the reaction performancesincreases.


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The question of the trainability of the reaction speed is still a disputed subject.Simkin claims 10 to 20% improvement through training. As a rule there is also adifference between athletes and non-athletes in favor of the athletes. However,this could be the result of conditioning.

Information on the reaction times in the l00m start in Seoul 1988 (final) for menand women are shown in Table 1. Particularly noticeable from the information isthat Joyner in 13.1 had a faster reaction time than Johnson in 13.2. On the other hand, there was no linear relationship between the reaction times and the l00mtimes of the athlete.

The deciding factor in the reaction performance is the functional capacity of thecentral nervous system (CNS) or, to be more precise, the participation of thesensors system, located in the skin, the muscles, tendons and ligaments for the

touching stimulus. The audio system reacts to acoustic and the optical system tovisual signals. These part-systems are extremely specialized, transmittingthrough different paths the stimuli to the central nervous system. This explainsthe specificity of the reaction times.

ACCELERATION

Acceleration is a measurement of velocity changes in movements. It is definedas the quotient of the velocity changes (∆V) and the time required for it (∆t):

___ ∆V ___ a =

∆t

The measuring unit is meter per second. A positive acceleration takes placewhen speed over the covered distance is increased, a negative accelerationoccurs when the speed over the covered distance is reduced.

A positive acceleration in the l00m sprint, admittedly, takes place only over thefirst few meters before it is changed to a negative acceleration after maximal


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velocity has been reached. This point for world’s best sprinters is around the 50mmark. As can be seen from Table 1, Johnson and Lewis reach maximal velocitybetween 50 and 60m, which means that they have accelerated up to this point.Even more impressive are the corresponding values for Joyner (Table 2).

Joyner accelerates to reach her maximal velocity of 10.98mIsec. between 60 and70m (!) and maintains this maximal value until 90m (!). The average accelerationover the section between 70 and 90m is therefore 0. Based on the aboveformula, the acceleration is up to 20m positive and after that up to 60m negative:

2.50 - 3.82 - 0.83 - 0.54 - 0.24 - 0.12 - 0.13.

Newton’s second law - strength = mass x acceleration - indicates that there is acorrelation between strength and acceleration. The available strength is on onehand regulated by the cross section of the muscles, on the other hand by theinter - and intramuscular coordination. The inter-muscular co-ordination is

responsible for the simultaneous activation of the highest possible number of motor units with the aim to create contraction in all available muscle fibres. Theterm co-ordination means here an improvement of the nerve-muscle cohesion.How the available strength can be most efficiently exploited is still a controversialsubject of the sprinting technique.

Particularly significant from a biomechanical viewpoint are, above all, ”theprinciple of the optimal acceleration path”, as well as “the principle of thebeginning strength”. The principle of the optimal acceleration path can besummed up as follows: “The available level of muscular strength and co-ordination capacity has to be used for an optimally long acceleration for body

movements that have to reach a high final velocity”. The length of an optimallyuseful acceleration path depends on the proportion of the breaking thrust with theacceleration drive. The principle of the beginning strength reads: “A bodymovement that has to reach a high final velocity must be initiated by a movementin the opposite direction. The breaking of the opposite movement provides in thebeginning a positive strength for acceleration, provided that the transfer occursfluently. This incr eases the acceleration drive”.

FREQUENCY

The factor of “frequency” in speed is defined as the alternating repetition speedand takes place only in cyclic speed movements. It should be treated from threeview points:

1. From the viewpoint of the muscle coordination guided by the brain;

2. From the viewpoint of the dependence on movement amplitude (stridelength in sprinting);

3. From the viewpoint of the movement range of the joints (mobility).


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Explanations:

1. Muscle co-ordination: The movement frequency, as the base for forwardpropulsion (wings of a bird), depends in principle on the alternatingactivation of antagonistic muscles. This complicated co-ordination

procedure is guided from the brain. “The cerebral pacemaker is located inthe stem of the brain.” It must be noted here that a cyclic movementpattern is not simply a chain of reflections.

2. Movement amplitude: It is plausible that speed in a cyclic movementperformance depends, next to the cerebral guidance, also on themovement amplitude. This means in sprinting that the stride frequencyand the stride length are closely related; although it is generally not clear under which conditions does the stride frequency or the stride lengthbecome the primary performance deciding component.

3. Mobility: It is certain that mobility, defined as the movement range of the joints, influences performance. Mobility depends on the elasticity of themuscles, as well as the mechanical construction of the joints and theflexibility of the tendons and ligaments.

In this context it is interesting to note some data on the world’s best sprinters inSeoul 1988:

Stride frequency (maximum): Johnson-5.02, Lewis-5.84, Joyner-4.68, Ashford 4.93 (strides per second between 30 and 60m).

Stride frequency (minimum): Johnson-4.61, Lewis-4.15, Joyner-4.35,

Drechsler-4.08 (strides per second between 0 and 30m).

Stride length (maximum): Johnson-2.42m, Lewis-2.65m, Joyner-2.40m, Ashford-2.19m, Drechsler-2.40m (between 60 and 90m).

Stride length (minimum): Johnson-1.71m, Lewis-1.85m , Joyner-1.69m, Ashford-1.61 m, Drechsler-1.78m (between 0 and 30m).

Total number of strides (0 to l0m): Johnson-46.6, Drechsler-46.4, Lewis-43.6, Ashford-50.8.

Although this is not the place to interpret this data in detail, three remarksnevertheless appear to be in order:

There is no rule for the time when the longest strides (largest amplitude)and the highest stride frequency occur (60 to 90m and 0 to 30m).


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Johnson and Drechsler take almost the identical number of strides, areclose in the maximal and minimal stride length, but differ in the stridefrequency in favor to Johnson. Their time difference exceeds one second.

Joyner has between 60 and 90m an average stride length of 2.40m, the

same as Drechsler. However, she has an average stride frequency of 4.58, in contrast to Drechsler’s 4.37 per second.

dimensions of motor speed - joch

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