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Journal of Exercise Physiologyonline
February 2013
Volume 16 Number 1
Editor-in-Chief
Official Research Journal of
Tommy
the American
Boone, PhD,
Society
MBA
of
Review
Board
Exercise
Physiologists
Todd Astorino, PhD
ISSN 1097-9751
Julien Baker,
PhD
Steve Brock, PhD
Lance Dalleck, PhD
Eric Goulet, PhD
Robert Gotshall, PhD
Alexander Hutchison, PhD
M. Knight-Maloney, PhD
Len Kravitz, PhD
James Laskin, PhD
Yit Aun Lim, PhD
Lonnie Lowery, PhD
Derek Marks, PhD
Cristine Mermier, PhD
Robert Robergs, PhD
Chantal Vella, PhD
Dale Wagner, PhD
Frank Wyatt, PhD
Ben Zhou, PhD
Official Research Journal
of the American Society of
Exercise Physiologists
ISSN 1097-9751
JEPonline
Investigation of Core Muscle Function through
Electromyography Activities in Healthy Young Men
Sijie Tan1, Liquan Cao2, Whitney Schoenfisch3, Jianxiong Wang3
1Department
of Health and Exercise Science, Tianjin University of
Sport, Tianjin, China, 2Tianjin Physical Fitness Research Center,
Tianjin University of Sport, Tianjin, China, 3Centre for Systems
Biology, Department of Biological and Physical Sciences, Faculty of
Sciences, University of Southern Queensland, Toowoomba, Australia
ABSTRACT
Tan S, Cao L, Schoenfisch W, Wang J. Investigation of Core Muscle
Function through Electromyography Activities in Healthy Young Men.
JEPonline 2013;16(1):45-52. The purpose of this study was to
investigate the electromyography (EMG) signal during eight isometric
core exercises. Eighty healthy men (average 24.9 ± 1.4 yrs with body
mass 64 ± 5 kg) participated as subjects. The surface EMG of the
core muscles of 30 subjects was measured during eight isometric
contractions and the EMG signal was recorded from core muscles.
The four actions with the higher integral EMG were further applied in
another group of 50 subjects to test their reliability. The isometric
exercise of 'side bridge with single-leg raise' resulted in a significantly
higher EMG than those of other exercises. This exercise showed a
good reliability (ICC=0.77). Three other exercises also presented high
EMG and ICC. In conclusion, the 'side bridge with single-leg raise'
exercise is the most suitable single body movement to measure the
functional capacity of core muscles in healthy young men.
Key words: Core Muscles, Isometric Activity, Electromyography,
Young Men
46
INTRODUCTION
Core muscles play a larger role in human physical activities than is often realized. The core muscles
are at work allowing posture maintenance, bending, twisting, and providing a stable spine for various
activities involving the extremities that are required in daily life and for most sports (7,10,15).
Therefore, as well as maintaining body stability and performing safely, core strength plays an
important role in preventing the development of lower back pain (LBP) and sports injuries during
physical activities (2,3,7,9,23).
There are 29 pairs of core muscles of the human body that are arranged within what can be
considered as the core ‘box.’ The front of the box is formed by the abdominals, with paraspinals and
gluteals as the back, the diaphragm forms the roof, and the pelvic floor and hip girdle musculature act
as the base (1,9,10,14). The core muscles cooperate with each other to provide the spine and pelvis
with stability, particularly when performing functional movements (10). This core stability has been
summarized as “the ability to control the position and motion of the trunk over the pelvis and leg to
allow optimum production, transfer and control of force and motion to the terminal segment in
integrated kinetic chain activities” (15, p. 189), and refers to the stability of the spine rather than the
strength of the actual muscles (9,27).
While most research of the core musculature has focused on athletes (10,15,21,24) and people with
LBP (9,17,22,26), it is also important to research in terms of maintaining body stability and decreasing
injury among non-athletic individuals (6,13). However, the current lack of reliable and valid testing
methods makes it difficult to measure core strength in the general population (1,9,10). The use of
electromyography (EMG) may be a possible way to establish a valuable measurement method of
core strength, as electrical activity of muscles has been associated with the forces produced by the
muscles (11). Thus, the purpose of this study was to investigate the EMG signals during isometric
muscle contractions, which are mainly achieved through the working of the core muscles in a group of
healthy young men. The outcome of this study should contribute to the development of a useful
method of measuring core strength.
METHODS
Subjects
Eighty healthy men (average 24.9 ± 1.4 yrs, body mass 64 ± 5 kg, body height 174 ± 4 cm) from a
college population participated in this study. None of the subjects engaged in regular exercise training
when they were enrolled. Thirty of the subjects had the surface EMG of their core muscles measured
during eight isometric contractions, while the remaining 50 subjects performed the reliability tests of
the four exercises which showed the highest integral EMG (iEMG) readings. Exclusion criteria for this
investigation included any individuals with known acute or chronic LBP. The details of the study were
described to the subjects, and a written informed consent was obtained from each subject. All
methods and procedures of this study were approved by the Ethics Committee of Tianjin University of
Sport, China.
Measured Core Muscle Exercises
Eight core muscle exercises are shown in Figure 1. There was a familiarization session during which
the 30 subjects learned how to perform the exercises. The testing session took place at least 3 days
after the familiarization session. Eight exercises were randomly tested on each subject with a 3-min
rest between the tests.
47
Exercise 1. Front bridge
Exercise 2. Front bridge with single-leg raise
Exercise 3. Bird dog
Exercise 4. Sit-up with double-leg raise
Exercise 5. Supine bridge
Exercise 6. Supine bridge with single-leg raise
Exercise 7. Side bridge
Exercise 8. Side bridge with single-leg raise
Figure 1. Summary of the Eight Exercises.
EMG Measurement
EMG signals from eight points of the core muscles (rectus abdominis high and low parts, external
oblique, latissimus dorsi, gluteus medius, gluteus maximus, longissimus, and multifidus) were
recorded using the EMG equipment (Noraxon Inc. USA). The surface electrode placement area was
shaved, abraded, and cleansed with alcohol to improve the conductivity of the EMG signal. The EMG
signals of each action were recorded for 10 sec while the subject performed and maintained the
exercise in the standard stable position. This 10-sec recording was analyzed for the iEMG using the
MyoResearch XP software (Noraxon Inc. USA).
Reliability Test
The four exercises with the highest iEMG were chosen and further applied in another group of 50
subjects to test their core muscle strength with a brief introduction before the first test. The function of
core strength was measured as the time period during which the subjects could maintain the standard
48
positions of the exercises. There was a 3-min rest period between action tests. Each subject of this
group produced duplicate measurements. The 2nd test took place 3 days later.
Data Analyses
All of the values were presented as mean ± SD. Differences in the iEMG between the exercises were
identified using one-way analyses of variance (ANOVA). When a significant F-ratio was obtained, a
post-hoc analysis with Bonferroni adjustment was used to identify which pair of mean values had
significant changes. The intraclass correlation coefficients (ICCs) for the reliability of the 4 exercises
were calculated. All statistical analyses were performed using the SPSS Version 11.5 for Windows
(SPSS Inc. USA). Alpha level was set 0.05.
RESULTS
The EMG for each of the core muscles during the 8 exercises is shown in Table 1. The Exercise 8:
side bridge with single-leg raise, showed a significantly higher iEMG (5949.9 ± 1129 uV, P<0.01) than
those of other exercises. The results of the other exercises were Exercise 7 (3878.9 ± 771.0 uV),
Exercise 2 (3387.2 ± 755.1 uV), Exercise 4 (3325.4 ± 856.7 uV), Exercise 1 (2638.3 ± 689.6 uV),
Exercise 3 (2055.4 ± 503.8 uV), Exercise 6 (1987.9 ± 509.5 uV), and Exercise 5 (1482.3 ± 501.6 uV).
Table 1. EMG of Different Core Muscles during Eight Actions (uV·10s). Data (Mean ± SD)
Ex 1
Ex 2
Ex 3
Ex 4
Ex 5
Ex 6
Ex 7
Ex 8
External
oblique
369.3
±
145.3
574.3
±
277.4
164.2
±
75.7
686.1
±
352.7
26.9
±
7.4
66.4
±
24.6
1051.7
±
315.2
1257.2
±
340.9
Rectus
abdominis
(high)
1019.9
±
365.8
568.2
±
207.7
58.9
±
22.8
1127.7
±
327.0
34.8
±
12.8
48.4
±
18.7
686.7
±
297.4
860.8
±
311.7
Rectus
abdominis
(low)
913.1
±
289.5
674.1
±
240.4
35.1
±
19.0
114.8
±
353.9
22.5
±
8.5
38.3
±
13.2
553.2
±
229.9
596.9
±
244.9
Latissimus
dorsi
176.6
±
82.3
169.9
±
77.8
139.5
±
43.0
65.8
±
21.7
128.7
±
50.3
101.4
±
69.4
190.9
±
74.2
275.3
±
96.7
Longissimus
48.8
±
14.2
57.0
±
21.5
227.5
±
93.3
54.1
±
21.7
353.7
±
152.7
401.8
±
144.1
287.6
±
88.1
456.8
±
222.7
Multifidus
43.4
±
12.4
123.3
±
46.6
415.6
±
168.5
106
±
43.9
496.4
±
196.1
547.8
±
209.5
302.4
±
139.9
440.8
±
169.4
Gluteus
medius
39.4
±
14.9
428.8
±
188.6
314.3
±
133.7
76.2
±
36.9
140.3
±
83.4
313.6
±
190.4
455.4
±
180.1
1231.1
±
400.8
Gluteus
maximus
27.8
±
6.74
691.7
±
204.6
700.4
±
293.1
68.7
±
21.2
338.5
±
159.1
470.2
±
173.9
351.4
±
140.9
831.8
±
263.9
49
The four exercises with the highest recorded iEMG (Exercise 8, 7, 2, and 4) were performed by 50
subjects on two occasions that were separated by at least 3 days. The average results and ICC
between the two tests are listed in Table 2.
Table 2. Reliability Test Results of Four Exercises.
Test 1 (s)
Test 2 (s)
ICC
Exercise 8
23.6 ± 6.8
25.3 ± 6.1
0.77**
Exercise 7
43.2 ± 8.8
48.6 ± 9.1
0.85**
Exercise 2
93.7 ± 20.5
106.4 ± 24.4
0.69*
Exercise 4
22.1 ± 4.2
26.4 ± 5.8
0.71**
All data are presented in Mean ± SD. *P<0.05; **P<0.01
DISCUSSION
The theoretical principle of using EMG to measure core strength came from Fuglevand’s report (11),
in which it has been stated that muscle electrical activities are closely associated with muscle forces
in isometric contractions, indicating that body movements which recruited more motor units from the
muscles would show a greater level of accumulated EMG activity. In the present study, we found that
Exercise 8, the side bridge with single-leg raise, showed the highest iEMG among the 8 exercises. It
indicates that Exercise 8 acts with the highest level of the core muscle recruitment, and its
performance reflects the functional capacity of the core muscles. This exercise can be performed by
healthy young people without difficulty. The average performance time is <30 sec, which is very
efficient to be tested, in particular, for the measurement of the core muscle function in large physical
education classes. The ICC of this exercise reached 0.77, which indicates that Exercise 8 has a high
testing reliability and can be used as a standard method of measurement of core muscle strength in
healthy young men. In addition, Exercise 7, 2, and 4 also demonstrated significantly high test-retest
reliability and, therefore, they are usable for core muscle strength measurement in young healthy men
as well.
Previous studies investigating the side bridge also indicated that the exercise had a high EMG. One
study (8) of 30 healthy subjects, males and females of ages 27 ± 8, demonstrated that the side bridge
could produce larger percentages of the maximum voluntary isometric contraction in certain core
muscles than other exercise, including the prone bridge (front bridge), unilateral-bridge (supine with
single-leg raise), bridge (supine), and quadruped (bird-dog). Ekstrom and colleagues (8) reported that
the side bridge produced the largest percentage of EMG activity in the gluteus medius, longissimus
thoracis, and external oblique abdominis, as well as the second and third highest percentage in the
rectus abdominis and lumbar multifidus, respectively. The findings by García-Vaquero and colleagues
(12) regarding healthy men and women aged 24.22 ± 5.23 and 22 ± 2.93, respectively, were similar
to ours, in that compared to the front and supine bridge actions, the side bridge elicited some of the
highest EMG activity in the external and internal obliques of the respective side being tested. The
EMG values increased when a leg was raised off of the underlying leg as for Exercise 8 of our study.
Numerous research studies suggest that a poorly developed core is linked to an increased risk of
injury and LBP (2,7,10,13,14,27). Conversely, when core is well developed, there is a statistical
decrease in the risk of injury and LBP (3,5,8,21,22,26). Having a strong and stable core is important,
especially for individuals who want to avert injury and/or pain. However, to study the function of the
core muscles requires the ability to reliably measure the capabilities of the musculature in the
50
subjects. This highlights the importance of the present study as our purpose was to investigate the
EMG signals during isometric muscle contractions and obtain information which may be useful in the
development of methods of measuring the activity of the core. It was found that Exercise 8: the side
bridge with single-leg raise produced the most activity within the core, and thus was the best indicator
in this investigation of the total capability of the core. Exercises 7, 2, and 4 produced the next highest
iEMG results and would also be effective indicators of core strength.
Limitations of the present study are that surface electrodes were used and the exchange of signals
between different core muscles could not be fully prevented (8). In this study, only the core muscle
from healthy young men was examined. As skeletal muscle strength and endurance vary largely
among different age and sex groups, it is not possible to have a single measurement method suitable
to all people. Therefore, the current outcome is only applicable to the sample subjects. Other age
groups, children in particular, would be studied in the future in an attempt to fill the knowledge gap
around the core musculature of children. The link between core muscle activation and LBP and other
injuries needs to be studied further to determine whether the results from the core activation
produced during certain exercises can provide an indication of a person’s risk of LBP or injury. Our
results were measured from solid-base exercises and did not employ the use of unstable devices or
surfaces. One study (4) reported that more EMG activity could be obtained from the exercises
performed on unstable surfaces. Such muscle actions should be considered with additional research.
CONCLUSION
Exercise 8 (side bridge with single-leg raise) showed the highest iEMG. Of all the exercises, it would
be the most suitable single body movement to measure the core muscle function. Further, this action
also demonstrated a good ICC in the reliability test. Three other actions (side bridge, front bridge with
single-leg raise, and sit-up with double straight-leg raise) are also good choices in the measurement
of the core muscle function in healthy young men.
ACKNOWLEDGMENTS
This project was supported by the Tianjin Educational Science Project (HE1016) and the Ministry of
Education of China (11YJAZH081).
Address for correspondence: Jianxiong Wang, Centre for Systems Biology, Faculty of Sciences,
University of Southern Queensland, Toowoomba QLD 4350, Australia. Telephone: 61-2-46312363.
E-mail: wangj@usq.edu.au
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