Effects of the Support Surface Condition

on Muscle Activity of Abdominalis

and Erector Spinae During

Bridging Exercise

Youngju Hong

The Graduate School

Yonsei University

Department of Rehabilitation Therapy

Effects of the Support Surface Condition

on Muscle Activity of Abdominalis

and Erector Spinae During

Bridging Exercise

Youngju Hong

The Graduate School

Yonsei University

Department of Rehabilitation Therapy

Effects of the Support Surface Condition

on Muscle Activity of Abdominalis

and Erector Spinae During

Bridging Exercise

A Masters Thesis

Submitted to the Department of Rehabilitation Therapy

and the Graduate School of Yonsei University

in partial fulfillment of the

requirements for the degree of

Master of Science

Youngju Hong

June 2009

This certifies that the master’s thesis of Youngju Hong

is approved.

Thesis Supervisor: Ohyun Kwon

Chunghwi Yi

Hyeseon Jeon

The Graduate School

Yonsei University

June 2009

Acknowledgements

As I finish my work on the thesis, memories from the graduate school days rush

back to me with swelling joy in the heart and many dear faces. First of all, I would

like to dedicate my accomplishment to the glory of God, who always guided me to

a right path, leading me to this point.

I extend my deepest gratitude to Professor Ohyun Kwon who expanded my

perspectives on the world and became my beacon even though I lacked so many

abilities and caused concern. My sincere gratitude also goes to Professor Chung-

hwi Yi who embraced me with wonderful kindness even when I made mistakes. I

would like to thank Professor Hyeseon Jeon for giving me encouragement and love

with her warm smile and heart. I also thank Professor Sanghyun Cho for giving me

clear guidelines in study and Professor Seunghyun Yoo for awakening spirit of

academic exploration in me.

I am much indebted to Jonghyuck Weon for taking care of me during my

graduate school years, as well as to Taeho Kim, Heonseock Cynn and KEMA

members.

My appreciation goes to Jaeseop Oh, Wonhwee Lee, Sungmin Ha, Sujeong Kim

and Kyuenam Park, all of whom are on the same path with me. I would also like to

thank Minhee Kim who is even more attentive than me in taking care of my work,

and to Jungran Kim for her generous advice and encouragement, and to Sujin

Hwang.

I bow my head deeply to show my appreciation to Father Hakgeun Lee who

became my spiritual support, gave me lessons of life, and enriched my life while I

worked at the KEMA center. Also, my gratitude goes to Yeonggil Jung, godmother,

sisters at nunnery, Professor Myoungbok Kim, Hyunsoon Cynn and other families

of the KEMA center.

Love that I receive from my greatest supporters, grandparents and parents,

nourishes my life. It becomes a solid ground when I go through difficult moments,

and I respect and love them for helping me to take root more strongly. I am also

thankful to sister Jeongwon who is my family and friend that extends helping hands

to me without hesitation, to my aunts and niece Doyun, my valuable friends whom

I can laugh with freely even when work is hectic and stressful, and the juniors at

the school who helped me greatly with experiments.

I will always remember my blessing and try to live up to the trust people have

shown in me. Thank you.

i

Table of Contents

List of Figures ·························································································· ⅱ

List of Tables ···························································································· iii

Abstract ···································································································· iv

Introduction ······························································································· 1

Method ······································································································ 5

1. Subjects ····························································································· 5

2. Experimental Equipments ·································································· 6

2.1 Electromyography System ··························································· 6

2.2 Apparatus of the Support Surface Conditions ······························· 8

3. Experimental Procedures ··································································· 9

3.1 Bridging Exercise ······································································· 10

3.2 Unilateral Bridging Exercise ······················································· 10

4. Statistical Analysis ··········································································· 13

Results ····································································································· 14

Discussion ································································································ 23

Conclusion ······························································································· 28

References ······························································································· 29

Abstract in Korean ··················································································· 35

ii

List of Figures

Figure 1. Surface conditions ········································································ 8

Figure 2. Bridging exercise under the three different support surface

conditions ··················································································· 11

Figure 3. Unilateral bridging exercise under the three different support

surface conditions ······································································· 12

Figure 4. EMG activities during the bridging exercise using three

different support surfaces ···························································· 17

Figure 5. EMG activities during the unilateral bridging exercise

using three different support surfaces ··········································· 19

iii

List of Tables

Table 1. Descriptive data for participants in this study ······························· 5

Table 2. Comparison of EMG activities according to the support

surface conditions during the bridging exercise ··························· 16

Table 3. Comparison of EMG activities according to the support

surface conditions during the unilateral bridging exercise ············ 18

Table 4. Comparison of EMG activities between the bridging exercise

and unilateral bridging exercise ··················································· 20

Table 5. Comparison of EMG activities between the right and left

sides during the bridging exercise ··············································· 21

Table 6. Comparison of EMG activities between the right and left

sides during the unilateral bridging exercise ······························ 22

iv

ABSTRACT

Effects of the Support Surface Condition

on Muscle Activity of Abdominalis and

Erector Spinae During Bridging Exercise

Youngju Hong

Dept. of Rehabilitation Therapy

(Physical Therapy Major)

The Graduate School

Yonsei University

Various exercise protocols have been designed to improve trunk stability in the

fields of rehabilitation and sport. Bridging exercise on the floor, foam roll, or gymball

is often prescribed for improving trunk stability.

The aim of this study was to determine the muscle activity of the abdominalis and

erector spinae during bridging and unilateral bridging exercises on a firm surface, on

the sit-fit, and on a foam roll. Eighteen healthy young subjects with no medical

v

history of lower-extremity or lumbar spine disease were recruited for this study.

Muscle activity was recorded using surface EMG electrods from the both sides of the

rectus abdominalis, external obliques, internal obliques, and erector spinae muscles

during bridging and unilateral bridging exercises. A one-way repeated analysis of

variance was used to compare the EMG activity of each muscle according to the

support surface condition. Differences in the EMG activities between the bridging

and unilateral bridging exercises, and between the right side and left side were

assessed using a paired t-test, and the level of statistical significance was set at 0.05.

The study showed that the EMG activities of the both rectus abdominalis, both

external obliques, and the right internal oblique were significantly higher when the

bridging exercise was performed using the foam roll than when using the sit-fit. The

EMG activities of the both external obliques, both internal obliques, and both erector

spinae during bridging exercise using the foam roll were significantly higher than that

using the firm surface. The EMG activities of the left rectus abdominis, both external

obliques, and the right internal oblique were significantly higher during unilateral

bridging exercise using the foam roll than when using the sit-fit. The EMG activities

of the right external oblique, right internal oblique, and both erector spinae during

unilateral bridging exercise using the foam roll were significantly higher than when

using the firm surface. The EMG activity of the left erector spina was significantly

higher when using the sit-fit than when using the firm surface during the unilateral

bridging exercise. The EMG activities of all of the muscles were significantly higher

during the unilateral bridging exercise than during the bridging exercise. There was

vi

no significant difference in the EMG activity of each muscle between the right side

and the left side during the bridging exercise. In the unilateral bridging exercise, the

EMG activity of the right rectus abdominis was significantly higher than that of the

left rectus abdominis in all three support surface conditions. In addition, the EMG

activity of the right erector spina was significantly higher than that of the left erector

spina when performing the unilateral bridging exercise using the firm surface and the

sit-fit.

Based on these fidings, performing the unilateral bridging exercise using the sit-fit

or the foam roll is a useful method for facilitating trunk-muscle strength and hence

lumbar stability.

Keywords: Abdominal muscles, Bridging exercise, Electromyography, Erector

spinae, Trunk stabilization exercise, Unstable support surface.

- 1 -

Introduction

Low back pain (LBP) is common, with 60% - 90% of the adult population being at

risk of developing LBP at some point in their lifetime (Smeal et al. 2004). Of those

who develop acute LBP, 30% develop chronic LBP (Khadilkar et al. 2005), which

has a significant impact on functional status and occupational activities, and marked

socioeconomic repercussions (Hagen et al. 2000; Philadelphia Panel 2001; Strand,

Moe-Nilssen, and Ljunggren 2002). Chronic LBP is the most frequent cause of

workers’ compensation claims and a major reason for visits to healthcare

professionals (Philadelphia Panel 2001).

The trunk muscles provide core stability to the trunk, which allows the trunk to

maintain a static posture even under the influence of destabilizing external torques

(Akuthota and Nadler 2004). LBP is caused by instability of the lumbar segment with

weakness of the trunk stabilizer muscles, and a lack of back muscle endurance (Hall

and Brody 2005; Neumann 2002). Poor coordination of the muscle corset around the

lumbar spine may also contribute to LBP (Andersson et al. 1997; Cholewicki and

VanVliet 2002).

Panjabi (1992) introduced an innovative model of a spinal stabilization system.

Spine stability is dependent on three subsystems: passive (spinal column), active

(spinal muscles), and control (neural control). Lumbar spine stability can be achieved

via coordinated force feedback from both the active and the passive structures, with

- 2 -

appropriate levels of activation to the contracting muscles in order to balance any

destabilizing force (Kavcic, Grenier, and McGill 2004). It is therefore essential that

stability is precisely controlled by lumbar and abdominal muscles to produce the

stiffness required to optimize the loading on the lumbar spine, and to prevent

overload injury (Arokoski et al. 2004).

Lumbar stability is increased with abdominal and paraspinal muscle coactivation,

which increases intra-abdominal pressure and produces an abdominal spring force

(McGillet et al. 2003). The abdominal muscles serve as a vital component of the core.

The internal oblique (IO) has a similar fiber orientation to the transverse abdominis,

thus increasing the intra-abdominal pressure together with the transverse abdominis.

Thus, the IO imparts functional stability to the lumbar spine (McGill 2002). The

external oblique (EO), the largest and most superficial of the abdominal muscles, acts

as an evaluator of anterior pelvic tilt. It is recruited to enhance spine stability,

generating lateral bending and twist torque of the trunk (Pool-Goudzwaard et al.

1998). The rectus abdominis (RA) is a paired, strap-like muscle of the anterior

abdominal wall contraction of which predominantly causes flexion of the lumbar

spine. The erector spinae (ESs) in the lumbar region act on the lumbar spine via a

long tendon that is attached to the pelvis. Contraction of the ESs extends the trunk, a

movement that is controlled largely by the opposing activity of the RA muscles. The

role of the multisegmental back muscle is to provide general trunk stabilization and to

balance external loads, thereby helping to minimize the forces acting on the spine

(Ebenbichler et al. 2001). The function and coordination of the muscles that stabilize

- 3 -

the lumbar spine are often impaired in patients with LBP (Cholewicki and VanVlient

2002).

During the past decade, many physical therapy rehabilitation interventions have

been used in the management of LBP (Khadilkar et al. 2005). Exercises are effective

in decreasing the intensity of LBP and the associated functional disability, and in

improving back extension strength, mobility, and endurance (Vezina and Hubley-

Kizey 2000). Recently the focus of lumbar stabilization exercises has been on

protecting the spinal joint structure from further repetitive microtrauma and restoring

dynamic stability to the trunk (Stevens et al. 2006). The lumbar stabilization exercises

include the so-called dying bug, quadruped, pelvic tilt, abdominal hollowing, and

bridging exercises (Barnett and Gilleard 2005; Hubley-Kozey and Vezina 2002). The

bridging exercise is commonly used for improving lumbopelvic stabilization. It is a

comfortable and typically painless posture for improving the coordination of the trunk

muscles (Hyde and Gengenbach 2007; Lehman, Hoda, and Oliver 2005; Stevens et al.

2006). The use of unstable support surfaces increases muscle activity and coactivation

for trunk and lumbar stability (Vera-Garcia, Grenier, and McGill 2000). Unstable

support surfaces such as gym balls, rollers, wobble boards, slings, and disks are often

used for stability exercises (Akuthota and Nadler 2004). According to a study by

Marshall and Murphy (2005), performing tasks on a Swiss ball leads to the abdominal

and spinal muscle activities being higher than those on a stable surface (Vera-Garcia,

Grenier, and McGill 2000). However, the Swiss ball has been the only type of

unstable surface examined in previous studies. Trunk and ESs EMG activities were

- 4 -

recently investigated during bridging stabilization exercises, ball bridging exercises,

and bridging exercises with leg movements (Stevens et al. 2006). However, the EMG

activities of the abdominal muscles and ESs during bridging and unilateral bridging

exercises under different support surface conditions were not analyzed. Therefore, in

the present study determined the effects of three different surface conditions (firm

surface, sit-fit, and foam roll) on abdominal muscles and ESs EMG activities during

bridging and unilateral bridging exercises.

- 5 -

Method

1. Subjects

A cohort of eighteen healthy young subjects (9men and 9women) without

neurological, musculoskeletal, or cardiopulmonary diseases, or back or lower-limb

pathology were recruited from the Department of Physical Therapy, Yonsei

University, Korea (Table 1). The subjects were assessed for their ability to perform

the bridging exercise and unilateral bridging exercise without pain. Prior to the study,

the principal investigator explained all of the procedures to the subjects in detail, and

obtained their written informed consent to participate.

Table 1. Descriptive data for participants in this study. (N=18)

Parameter Mean ± SD Range

Age (years) 23.17 ± 2.09 21~26

Body mass (㎏) 61.33 ± 9.89 46~81

Height (㎝) 170.56 ± 9.19 156~190

- 6 -

2. Experimental Equipments

2.1 Electromyography System

EMG data were collected using a Noraxon TeleMyo 2400 system (Noraxon Inc.,

Scottsdale, AZ, USA.) and analyzed using MyoResearch Master Edition 1.06 XP

software (Noraxon Inc., Scottsdale, AZ, USA). The skin was prepared by shaving the

hair and then rubbing it with sandpaper and an alcohol/water solution to decrease the

skin impedance. Surface electrode pairs and the adhesive skin interfaces were

separated by 2 cm. The reference electrode was attached to the right anterior superior

iliac spine (ASIS). The eight electrode sites on both sides were as follows: the RA

(parallel to approximately 3cm lateral and superior to the umbilicus, arranged along

the longitudinal axis, over the muscle belly), IO (halfway between the ASIS of the

pelvis and the midline, just superior to the inguinal ligament), EO (halfway between

the ASIS of the pelvis and the inferior border of the rib cage at a slightly oblique

angle, running parallel to the underlying muscle fibers), and lumbar ES (parallel to

the spine, approximately 2 cm lateral to the L4 - L5 spinous process for the lumbar

ES, over the muscle belly) (Cram, Kasman, and Holtz 1998).

The raw signal was full-wave rectified and filtered using a Lancosh FIR digital

filter. The bandpass filter was set between 20 and 500 Hz and the notch filter at 60 Hz.

The sampling rate was 1000 Hz. The EMG data were processed into the root mean

square (RMS) value, which was calculated from 300-ms windows of data points. For

- 7 -

normalization of the EMG data, the mean RMS of three trials of 5-second maximal

voluntary isometric contractions (MVICs) was calculated for each muscle. The

manual muscle testing positions selected for the MVIC were those recommended by

Kendall et al. (2005). For the testing of the bridging and unilateral bridging exercises,

the EMG signal was collected for 5 seconds while the subject’s pelvis was maintained

level with the hip in a neutral position. The data for each trial are expressed as a

percentage of the MVIC (%MVIC), and the mean value of three trials was used for

analysis.

- 8 -

2.2 Apparatus of the Support Surface Conditions

The exercises were performed using three different support surfaces: firm surface,

sit-fit, and round foam roll (Figure 1). The height of the 14 cm diameter foam roll was

matched with the firm surface and sit-fit height. The subjects laid supine on the floor

with their feet flat on the experimental surface.

Figure 1. Surface conditions. A: Firm surface, B: Sit-fit, C: Foam roll.

A B C

- 9 -

3. Experimental Procedures

All subjects attended an orientation (practice) session that lasted at least 30 minutes

before testing to familiarize themselves with the bridging and unilateral bridging

exercises using the different support surface conditions. The start position of all

exercises was hook-lying with the feet flat on the support surface. The positions of

both the subject and the equipment were standardized by placing markers on the floor.

Tests were performed in a random order. The bridging position was held for five

seconds, and three trials were performed for each exercise. A 30-second rest period

was allocated between the trials, and a 3-minute rest period was allocated between the

different support surface conditions.

- 10 -

3.1 Bridging Exercise

The subjects assumed a supine position on the floor with the head, upper trunk, and

pelvis in a straight line. The knees were bent to 60° and the hands were placed onto

the chest. The feet were placed shoulder-width apart on the support surface being

tested. The subjects lifted their pelvis until the hip joint reached a neutral position

(Figure 2). At the beginning of each exercise, a neutral lumbar spine position was

determined by the examiner and the subjects were encouraged to hold this position

during the course of the exercise. Feedback from the examiner was given in order to

achieve a consistent spine and lower-limb posture during the bridging exercise.

3.2 Unilateral Bridging Exercise

This testing procedure was similar to that of the bridging exercise, except that the

right knee joint was extended during the bridging exercise position (Figure 3), and

also took place using the three different support surfaces. The target bar was placed at

the level of 0° of knee extension, and subjects were instructed to extend their knee

without hip adduction, abduction, or pelvic tilt until the tiptoe region of the right side

touched the target bar.

- 11 -

Figure 2. Bridging exercise under the three different support

surface conditions. A: Firm surface, B: Sit-fit, C: Foam roll.

A

B

C

- 12 -

Figure 3. Unilateral bridging exercise under the three different

support surface conditions. A: Firm surface, B: Sit-fit, C: Foam roll.

A

B

C

- 13 -

4. Statistical Analysis

The data are expressed as mean ± standard deviation (SD) values. Repeated one-

way analysis of variance (ANOVA) was used to compare the EMG activities of the

abdominalis and ESs according to the support surface condition. The Bonferroni’s

post-hoc test was used to determine the differences in EMG activities of the

abdominalis and ESs between the different support surface conditions. The

significance of differences in the EMG activity between the bridging and unilateral

bridging exercises, and between the right side and left side were assessed using a

paired t-test. Data analysis was performed using SPSS version 12.0 software, and the

level of statistical significance was set at 0.05.

- 14 -

Results

The EMG activities of all of the abdominalis and the ESs differed significantly

among the different support surfaces during the bridging exercise (p < 0.05) (Table 2).

Post-hoc testing revealed that the EMG activities of both RAs, both EOs, and the

right IO were significantly higher when performing the bridging exercise using the

foam roll than when using the sit-fit. The EMG activities of both EOs, both IOs, and

both ESs when performing the bridging exercise were significantly higher when using

the foam roll than when using the firm surface. None of the muscle EMG activities

when performing the bridging exercise differed significantly between using the firm

surface and the sit-fit (Figure 4).

The EMG activities of the right RA, right EO, right IO, and both ESs differed

significantly among the different support surfaces during the unilateral bridging

exercise (p < 0.05) (Table 3). Post-hoc testing revealed that the EMG activities of the

left RA, both EOs, and the right IO when performing the unilateral bridging exercise

were significantly higher when using the foam roll than when using the sit-fit. The

EMG activities of the right EO, right IO, and both ESs when performing the unilateral

bridging exercise were significantly higher when using the foam roll than when using

the firm surface. The EMG activity of the left ES when performing the unilateral

bridging exercise was significantly higher when using the sit-fit than when using the

firm surface (p < 0.05) (Figure 5).

- 15 -

The EMG activity of each individual muscle was significantly higher during the

unilateral bridging exercise than during the bridging exercise (Table 4). There was no

significant difference in the EMG activity of each muscle between the right and the

left sides during the bridging exercise (Table 5). However, when performing the

unilateral bridging exercise the EMG activity of the right RA was significantly higher

than that of the left RA in all three support surface conditions. The EMG activity of

the right ES was also significantly higher than that of the left ES when performing the

unilateral bridging exercise using the firm surface and the sit-fit (Table 6).

16

Table 2. Comparison of EMG activities according to the support surface conditions during the bridging exercise.

*p<0.05 a mean ± SD. RA: rectus abdominis, EO: external oblique, IO: internal oblique, ES: erector spinae.

Muscle

Surface

SS F p

Firm Surface Sit-Fit Foam Roll

Right RA 4.38 ± 3.42 a 4.90 ± 4.54 6.42 ± 6.00 40.645 3.893 0.03 *

Left RA 4.30 ± 3.48 4.40 ± 3.42 6.69 ± 6.29 65.711 5.531 0.002 *

Right EO 4.96 ± 4.20 5.60 ± 3.78 8.72 ± 6.98 146.056 10.211 0.000 *

Left EO 5.60 ± 4.06 5.93 ± 3.62 9.93 ± 7.22 209.608 10.819 0.000 *

Right IO 5.03 ± 4.07 6.80 ± 6.70 11.44 ± 10.53 394.211 6.709 0.003 *

Left IO 5.91 ± 4.11 7.97 ± 6.82 13.86 ± 12.06 611.662 7.958 0.001 *

Right ES 31.02 ± 10.77 34.55 ± 8.86 35.74 ± 9.08 216.936 5.361 0.009*

Left ES 32.27 ± 10.14 35.35 ± 8.01 37.25 ± 7.76 227.154 7.660 0.002 *

-16-

17

Right RA Left RA Right EO Left EO Right IO Left IO Right ES Left ES0

10

20

30

40

50

FS SF FR

* * *

* *

*

*

* * *

*

%M

VIC

Figure 4. EMG activities during the bridging exercise using three different support surfaces. FS; firm surface, SF:

sit-fit, FR: foam roll. RA: rectus abdominis, EO: external oblique, IO: internal oblique, ES: erector spinae. *p<0.05 (mean ± SD).

-17-

18

Table 3. Comparison of EMG activities according to the support surface conditions during the unilateral bridging exercise.

*p<0.05 a mean ± SD. RA: rectus abdominis, EO: external oblique, IO: internal oblique, ES: erector spinae.

Muscle

Surface

SS F p

Firm Surface Sit-Fit Foam Roll

Right RA 17.16 ± 13.64 a 21.84 ±19.67 25.35 ± 22.91 607.542 5.753 0.007 *

Left RA 9.72 ± 7.29 10.92 ± 9.45 13.08 ± 11.38 78.757 3.151 0.056

Right EO 19.20 ± 11.12 23.19 ± 12.37 27.40 ± 12.68 604.529 10.821 0.000 *

Left EO 20.32 ± 13.49 21.82 ± 11.48 26.25 ± 14.62 342.938 2.846 0.072

Right IO 32.09 ± 22.70 37.55 ± 23.83 46.38 ± 27.64 1871.347 7.350 0.002 *

Left IO 26.13 ± 21.82 31.61 ± 22.15 37.46 ± 27.23 1156.059 3.214 0.053

Right ES 43.15 ± 14.43 50.11 ± 11.99 52.90 ± 11.25 907.357 10.312 0.000 *

Left ES 39.95 ± 11.82 44.82 ± 9.13 47.31 ± 8.57 662.838 11.510 0.000 *

-18-

19

Right RA Left RA Right EO Left EO Right IO Left IO Right ES Left ES0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

*

*

*

*

*

*

*

* *

FS FRSF

%M

VIC

Figure 5. EMG activities during the unilateral bridging exercise using three different support surfaces. FS; firm surface,

SF: sit-fit, FR: foam roll. RA: rectus abdominis, EO: external oblique, IO: internal oblique, ES: erector spinae. *p<0.05 (mean ± SD).

-19-

20

Table 4. Comparison of EMG activities between the bridging exercise and unilateral bridging exercise.

* p<0.05 a mean ± SD. R: right, L: left.

RA: rectus abdominis, EO: external oblique, IO: internal oblique, ES: erector spinae. B: bridging exercise UB: unilateral bridging exercise.

Muscle Firm Surface t p Sit-Fit t p Foam Roll t p

RRA B

UB

4.38 ± 3.42 a

17.16 ± 13.64 -4.529 0.000*

4.90 ± 4.54

21.84 ± 19.67 -4.151 0.001*

6.42 ± 6.00

25.35 ± 22.91 -4.113 0.001*

LRA B

UB

4.30 ± 3.48

9.72 ± 7.29 -5.046 0.001*

4.40 ± 3.42

10.92 ± 9.45 -4.130 0.001*

6.69 ± 6.29

13.08 ± 11.38 -4.354 0.001*

REO B

UB

4.96 ± 4.20

19.20 ± 11.12 -6.358 0.001*

5.60 ± 3.78

23.19 ± 12.37 -6.869 0.001*

8.72 ± 6.98

27.40 ± 12.68 -7.703 0.001*

LEO B

UB

5.60 ± 4.06

20.32 ± 13.49 -5.622 0.001*

5.93 ± 3.62

21.82 ± 11.48 -6.756 0.001*

9.93 ± 7.22

26.25 ± 14.16 -5.803 0.001*

RIO B

UB

5.03 ± 4.07

32.09 ± 22.70 -5.627 0.001*

6.80 ± 6.70

37.55 ± 23.83 -6.225 0.001*

11.44 ± 10.53

46.38 ± 27.64 -6.147 0.001*

LIO B

UB

5.91 ± 4.11

26.13 ± 21.82 -4.307 0.001*

7.97 ± 6.82

31.61 ± 22.15 -4.980 0.001*

13.86 ± 12.06

37.46 ± 27.23 -4.354 0.001*

RES B

UB

31.02 ± 10.77

43.15 ± 14.43 -7.183 0.001*

34.55 ± 8.86

50.11 ± 11.99 -12.914 0.001*

35.74 ± 9.08

52.90 ± 11.25 -9.105 0.001*

LES B

UB

5.60 ± 4.06

39.95 ± 11.82 -3.602 0.002*

35.35 ± 8.01

44.82 ± 9.13 -6.266 0.001*

37.25 ± 7.76

47.31 ± 8.57 -5.099 0.001*

-20-

21

Table 5. Comparison of EMG activities between the right and left sides during the bridging exercise.

*p<0.05 a mean ± SD. Rt: right side, Lt: left side. RA: rectus abdominis, EO: external oblique, IO: internal oblique, ES: erector spinae.

Muscle Firm Surface t p Sit-Fit t p Foam Roll t p

RA

Rt 4.38 ± 3.42 a

0.160 0.875

4.90 ± 4.54

0.688 0.500

6.42 ± 6.00

-0.309 0.761

Lt 4.30 ± 3.48 4.40 ± 3.42 6.69 ± 6.29

EO

Rt 4.96 ± 4.20

-1.058 0.305

5.60 ± 3.78

-0.555 0.586

8.72 ± 6.98

-1.513 0.149

Lt 5.60 ± 4.06 5.93 ± 3.62 9.93 ± 7.22

IO

Rt 5.03 ± 4.07

-1.262 0.224

6.80 ± 6.70

-1.730 0.102

11.44 ± 10.53

-1.283 0.217

Lt 5.91 ± 4.11 7.97 ± 6.82 13.86 ± 12.06

ES

Rt 31.02 ± 10.77

-1.021 0.321

34.55 ± 8.86

-0.771 0.451

35.74 ± 9.08

-1.361 0.191

Lt 32.27 ± 10.14 35.35 ± 8.01 37.25 ± 7.76

-21-

22

Table 6. Comparison of EMG activities between the right and left sides during the unilateral bridging exercise.

*p<0.05 a mean ± SD. Rt: right side, Lt: left side. RA: rectus abdominis, EO: external oblique, IO: internal oblique, ES: erector spinae.

Muscle Firm Surface t p Sit-Fit t p Foam Roll t p

RA

Rt 17.16 ± 13.64 a

2.809 0.013*

21.84 ± 19.67

3.048 0.007*

25.35 ± 22.91

3.292 0.004*

Lt 9.72 ± 7.29 10.92 ± 9.45 13.08 ± 11.38

EO

Rt 19.20 ± 11.12

-0.741 0.469

23.19 ± 12.37

0.735 0.427

27.40 ± 12.68

0.499 0.624

Lt 20.32 ± 13.49 21.82 ± 11.48 26.25 ± 14.62

IO

Rt 32.09 ± 22.70

1.734 0.101

37.55 ± 23.83

1.491 0.154

46.38 ± 27.64

1.951 0.068

Lt 26.13 ± 21.82 31.61 ± 22.15 37.46 ± 27.23

ES

Rt 43.15 ± 14.43

2.115 0.049*

50.11 ± 11.99

2.298 0.035*

52.90 ± 11.25

2.097 0.051

Lt 39.95 ± 11.82 44.82 ± 9.13 47.31 ± 8.57

-22-

-23-

Discussion

The stability of the lumbar spine requires both the passive stiffness provided by

the osseous and ligamentous structures, and the active stiffness provided by muscles

that are under the motor control of the central nervous system (Ebenbichler et al.

2001; McGill et al. 2003). The spinal structure plays a role, but damage to the spinal

segments can be compaensated by proper muscular function and adequate neural

control, which is why exercise training is the mainstay of treatment to improve

stabilization of the spine (Barr, Griggs, and Cadby 2005). Thus, trunk stabilization

exercises are often used in the rehabilitation of individuals with LBP. Unstable

surfaces have been commonly incorporated into trunk strengthening exercise regimes

and recommended as a means of more effectively training the stability of the

musculoskeletal system (Behm et al. 2005; Lehman, Hoda, and Oliver 2005).

Numerous studies have documented increased trunk muscle activity during a variety

of trunk muscle exercises on unstable surfaces such as gym balls, rollers, wobble

boards, slings, and disks (Arokoski et al. 2001; Lehman, Hoda, and Oliver 2005; Mori

2004; Stevens et al. 2006; Vera-Garcia, Grenier, and McGill 2000).

The effects of three different support surface conditions on abdominalis and ESs

muscle activities during bridging and unilateral bridging exercises were examined in

the present study. The EMG activities of both RAs, both EOs, and the right IO when

performing the bridging exercise were significantly higher when using the foam roll

-24-

than when using the sit-fit. In addition, the EMG activities of the both EOs, and both

IOs when performing the bridging exercise using the foam roll were approximately

two times higher than when using the firm surface. The EMG activities of the

contralateral RA, both EOs, and ipsilateral IO when performing the unilateral briging

exercise were significantly higher when using the foam roll than when using the sit-fit.

Those of the ipsilateral EO, ipsilateral IO, and both ESs when performing the

unilateral bridging exercise were significantly higher when using the foam roll than

when using the firm surface. The EMG activity of the contralateral ES was

significantly higher during the same exercise when using the sit-fit than when using

the firm surface. The findings of this study thus demonstrate that when performing

the bridging and unilateral bridging exercises, the EMG activities of the abdominalis

and ESs were significantly higher when using the sit-fit and foam roll (unstable

surfaces) than when using the firm surface (stable surface). These increased

abdominalis and ESs EMG activities when using an unstable surface are in

accordance with the findings of Arokosiki et al. (2001) and Vera- Garcia, Grenier,

and McGill (2000). Vera-Garcia and his colleagues (2000) reported that the EMG

activities of both RAs, EOs, and IOs were higher when performing exercises on a

gym ball than when using a stable surface. This increased EMG activity was

attributed to the increased need for spine and whole-body stability in order to reduce

the threat of falling off the unstable surface. A more unstable support area requires

more muscle activity to maintaining balance.

-25-

In the present study, the EMG activities of all of the abdominalis when performing

bridging exercise were significantly higher when using the foam roll than when using

the sit-fit. There are several possible explanations for this finding. First, the

cylindrical shape of the foam roll provides a smaller contact area on the floor and

moves easily from side to side; therefore, more challenging balancing reactions are

required during bridging exercise when using foam roll than when using the sit-fit,

with its flat lower surface (i.e. normal to the floor) (Creager 2006). Second, the

contact area between the subject’s foot and the support surface of the foam roll is

smaller than with the sit-fit. Finally, the smaller contact area between the foot and the

foam roll may have resulted in a reduced somatosensory input, and thus a

concomitant reduction in feedback, possibly causing an increase in the EMG

activities of the abdominalis (Shumway-Cook and Woollacott 2001).

In this study, the EMG activities of the abdominalis and ESs were significantly

higher during the unilateral bridging exercise than during the bridging exercise. The

contact area between the subject’s feet and the support is smaller when performing the

unilateral bridging exercise than when performing the bridging exercise. Thus,

maintaining a neutral spine without rotation during the unilateral bridging exercise is

a more challenging task, requiring more abdominalis contraction than the bridging

exercise (Behm and Anderson 2006; Shumway-Cook and Woollacott 2001).

Instability is induced not only by unstable surfaces, but also by destabilizing torque

such as that resulting from the unbalanced movement of lifting a leg (Behm et al.

-26-

2005). Due to the instability of the unilateral bridging exercise, muscle crossing the

abdominal area needs to cocontract more to maintain the unilateral bridging exercise

without spine rotation, hip flexion, and pelvic tilt than in the bridging exercise. The

weight of the lifted leg produces torque about spine rotation, hip flexion, and pelvic

tilt. To counterbalance this rotation moment, the RA, EO, and IO muscles of the

contralateral side contract to maintain trunk stability (Pool-Goudzwaard et al. 1998).

This instability can be overcome by cocontraction of the abdominalis not by

contraction of a particular muscle. Spinal stability can be maintained during the

unilateral bridging exercise only by elevating the intra-abdominal pressure by

simultaneously contracting all of the trunk muscles (Ebenbichler et al. 2001; Hodges

and Richardson 1996; Hodges et al. 2005).

The major finding of this study was that the EMG activity of the right RA was

significantly higher than that of the left RA during the unilateral bridging exercise in

all three support surface conditions. In addition, the EMG activity of the right ES was

significantly higher than that of the left ES during the unilateral bridging exercise

using both the firm surface and the sit-fit. Both the RA and the EO muscles play a

role in stabilizing the trunk and pelvis (Mori 2004). The EOs stabilize the trunk by

preventing mediolateral rotation as a result of their attachment to the thoracolumbar

fascia. On the other hand, the RA muscles have a more longitudinal action on the

trunk, and are a better stabilizer of anteroposterior tilting of the pelvis (Neumann

2002). Performing the unilateral bridging exercise activated the right RA, and the

-27-

right ES, because the subjects were asked to maintain the static equilibrium of the

body during the unilateral bridging exercise (right knee extension).

The weight of the lifted leg causes a hip extension moment. This should be

counterbalanced by the activation of the hip flexors to maintain the neutral position of

trunk. Increased hip flexor muscle activation will cause anterior pelvic tilt of the right

side. Anterior pelvic tilt is prevented by contraction of the right RA. This may be why

the activity of the right RA was greater during the unilateral bridging exercise than

during the bridging exercise (Marshall and Murphy 2005). The activation of the right

ES may also be increased to counterbalance the activation of the right RA.

The support surface conditions influenced the activities of the abdominal muscles

and ESs during spine stabilizing exercises. The findings of this study should aid the

design of new trunk stabilization exercises.

There were some limitations to this study. First, our results cannot be generalized

to other populations because all of the subjects who participated in the study were

healthy and young. Therefore, the effects of surface condition on trunk muscles

during stabilizing exercises should be confirmed in a patient population. Second, the

activities of the deep muscles that are considered to be trunk stabilizers, such as the

transverse abdominis, multifidus, and pelvic floor muscles were not measured.

-28-

Conclusion

The effects of the support surface condition on the EMG activities of the

abdominalis and ESs during bridging and unilateral bridging exercises were

investigated. Overall, these exercises activated the abdominalis and ESs more when

they were performed using the sit-fit and foam roll (the unstable surfaces) than when

using the firm surface (the stable surface). In addition, the EMG activities of the

abdominalis and ESs were higher when performing the unilateral bridging exerise

than during the bridging exercise. The EMG activity of the right RA was significantly

higher than that of the left RA under all three support surface conditions during the

unilateral bridging exercise. The EMG activity of the right ES was significantly

higher than that of the left ES when performing the unilateral bridging exercise using

the firm surface and the sit-fit.

-29-

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-35-

국 요약

각운동 수행 시 지지면 조건이 복근

척추 립근 근 도에 미 는 향

연 학 학원

재 학과( 리 료학 공)

주

재 스포 분야에 체간안 증진시키 하여 다양한

운동 실시하고 있다. 단단한 지지면, 폼 (foam roll), 료용 공(gym

ball) 이용한 각운동 체간안 운동 하나 히 행해진다.

본 연구 목 단단한 지지면, 싯핏(sit-fit), 원 폼 (foam roll)

3 가지 지지면에 각운동과 각운동 시 한쪽 다리를 편 운동 시 복근

척추 립근 근 도를 알아보 하여 실시하 다. 요통

과거 이 없는 건강한 인 18 명 상 실시하 다. 각운동과

각운동 시 한쪽 다리를 편 운동 수행 할 양 복직근, 외복사근,

-36-

내복사근, 척추 립근 근 도를 면 근 도 분 시스

이용하여 하 다. 각 근 근 도는 복 일원

분산분 (one-way repeated ANOVA) 사용하여 지지면 간 차이를

하 다. 각운동과 각운동 시 한쪽 다리를 편 운동 사이 근

도 각 근 좌∙우 근 도 차이는 짝 t-검 통하여

하 고, 수 α=0.05 하 다. 연구결과 각운동 시 양쪽

복직근, 외복사근, 른쪽 내복사근 근 도는 싯핏보다 폼 에

하게 높았다. 각운동 시 폼 에 양쪽 외복사근, 내복사근, 척추

립근 근 도는 단단한 지지면에 보다 하게 높았다. 각운동

시 한쪽 다리를 편 운동 시 왼쪽 복직근, 양쪽 외복사근, 른쪽

내복사근 근 도는 싯핏보다 폼 에 하게 높았다. 각운동 시

한쪽 다리를 편 운동 시 폼 에 른쪽 외복사근, 내복사근, 양쪽

척추 립근 근 도는 단단한 지지면에 하게 높았다. 각운동

시 한쪽 다리를 편 운동 시 왼쪽 척추 립근 근 도는 단단한

지지면에 보다 싯핏에 하게 높았다. 각운동 시행 보다 각운동

시 한쪽 다리를 편 운동 시행할 모든 복근 척추 립근 근

도가 하게 높았다. 각운동 시 복근 척추 립근 좌∙우

근 도는 한 차이가 없었다. 다른 3 가지 지지면에

각운동 시 한쪽 다리를 편 운동 시행 시 른쪽 복직근 근 도가

-37-

왼쪽 복직근 근 도보다 하게 높았다. 단단한 지지면과

싯핏에 각운동 시 한쪽 다리를 편 운동 시행 시 른쪽 척추

립근 근 도가 왼쪽 척추 립근 근 도보다 하게 높았다.

이러한 결과에 근거하여 싯핏이나 폼 에 각 운동시 한쪽 다리를

편 운동 실시하는 것 체간안 증진시키는데 효과 인 법이라고

할 수 있겠다.

핵심 는 말: 각운동, 근 도, 복근, 불안 한 지지면, 척추 립근,

체간안 운동.