TRUNK MUSCLE STRENGTH AND ENDURANCE BETWEEN NORMAL
WEIGHT AND OVERWEIGHT FEMALES
Duangrudee Taworn1,*, Wunpen Chansirinukor2,#, Wattana Jalayondeja3
1
Master student, Master of Science (Physical Therapy) Program, Faculty of Physical
Therapy, Mahidol University, Thailand
2,3
Faculty of Physical Therapy, Mahidol University, Thailand
*e-mail: duangrudee_ta@hotmail.com #e-mail: wunpen.cha@mahidol.ac.th
Abstract
Overweight persons tend to undergo health problems. An increased body weight in
association with excessive mechanical load has an effect on force distribution through joints.
In addition, most overweight persons have visceral fat accumulating around their abdomen
and waist. As a result, the trunk muscles tend to generate more force to support the structures
around the spine and are likely to produce low back problems. The physical appearance of
overweight persons may affect trunk muscle performance including strength and endurance.
This study aimed to compare the trunk muscle strength and endurance in normal weight and
overweight females. Sixty females aged between 20-35 years were categorized into two
groups – normal weight and overweight groups – according to their body mass index.
Strength and endurance of all participants’ trunk muscles were randomly tested. The trunk
muscle strength was tested as an isometric test by using the Biodex II dynamometer in sitting
90 degree position. Four positions of the trunk muscle endurance were tested including
extension, flexion, right and left side bridge. Trunk muscle strength and endurance data were
analyzed by using independent sample t-test. The results showed that the trunk extension and
flexion endurance time of normal weight group was significantly longer than that of
overweight groups. In conclusion, the normal weight females had greater trunk extensor and
flexor muscle endurance than the overweight females.
Keywords: isometric trunk muscle strength, endurance, overweight, females
Introduction
Nowadays, many people tend to undergo obesity, which is common regardless of age
or sex. The prevalence of the overweight and obese persons exists in many segments of the
population. The data from the World Health Organization (WHO) revealed that the
prevalence of Thai overweight and obese persons in 2010 were 39.9% for females and 28.3%
for males (1). The WHO defined the term “overweight and obesity” as abnormal or
excessive fat accumulation that was prone to health risk (2). For Asian population, cutoff
levels of body mass index (BMI) for the overweight and obesity persons are as follows: BMI
≥ 25 kg/m2 and a range of 23.0-24.9 kg/m2, respectively (3, 4). The causes of excessive
weight vary according to body fat related to a complex interplay of genetic, nutritional,
physiological, psychological, environmental, and social factors.
Moreover,
pathophysiological mechanism of obese persons are different from non-overweight or nonobese persons such as mechanism of appetite and food intake, adipose storage pattern which
are regulated from hormonal and endocrine systems (5). The overweight and obese persons
tended to suffer from chronic health conditions (6), for example, cardiovascular disease (7),
glomerular injury (8) and musculoskeletal problems [eg osteoarthritis knee and low back pain
(LBP)] (9, 10). It was reported that the BMI, waist circumference, hip circumference, and
waist-to-hip ratio were associated with LBP in females (11), that is, the obese persons tend to
have LBP. As stated earlier, most obese persons were prevalent in females. It was probable
that less trunk muscle strength was found in association with overweight or obese persons.
There were a few studies previously investigated muscle strength in normal weight
and obese persons. For example, Danneskiold-Samsoe (12) investigated muscle strength of
various muscle groups in normal weight healthy persons. The result showed decreased
muscle strength from age 40 to 49 years in both males and females. Miyatake (13) compared
grip and leg muscle strength between obese and non-obese persons. The results showed that
the muscle strength of obese persons was higher than that of non-obese persons whose age
was less than 60 years. Moreover, Hulens (14) investigated the differences in various muscle
strength between obese and normal weight sedentary females. The results showed that
absolute trunk flexor and extensor muscle strength of obese females were stronger than that
of normal weight persons. On the other hand, no significant difference of hand grip strength
between obese and normal weight females was found.
Muscle endurance is categorized into two types: isometric and dynamic muscle
endurance. Regarding the isometric muscle endurance, it is an ability of muscles or group of
muscles contraction against resistance to maintain contraction in one position. The outcome
of this endurance is “endurance time”, which is the period of time that muscles can perform
sustained contraction in static position (15). Static trunk extensor muscle endurance has been
used as an indicator for LBP (16). Impairment of trunk muscle endurance may be associated
with low back problems (17, 18).
A few studies were carried out to investigate trunk muscle endurance in healthy
participants. Investigating back muscle endurance by using the Sorensen test, Kankaanpaa
(19) studied influence of age, sex and BMI on back and hip extensor muscle fatigue. The
results showed that BMI had an influence on lumbar muscle fatigability for both sexes,
especially in females. Kriangchieocharn (20) investigated trunk muscle endurance in 20-49
years sedentary Thai workers and found that females had longer trunk extensor endurance
time than males, while males had longer trunk side bridge endurance time than females.
Moreover, Chan (21) studied trunk muscle endurance in intercollegiate male rowers and
reported that trunk flexor muscle endurance time was longer than trunk extensor and side
bridge endurance time.
As stated earlier, the obese persons tend to have LBP and most obese persons were
prevalent in females. Moreover, Thong-on (22) compared trunk muscle endurance in terms
of time and ratio among persons with and without LBP. The results were in accordance with
Moffroid’s study (23) that showed significantly more decreased endurance time in persons
with non-specific LBP than persons without LBP. Although few of studies were previously
conducted to investigate trunk strength and endurance in participants with and without LBP,
the comparison of strength and endurance between normal weight and overweight persons
was not explored. This study aimed to compare trunk muscle strength and endurance
between normal weight and overweight females.
Methodology
Sixty females aged between 20-35 years old participated in this study. There were
thirty females in each group. The participants were classified into two groups: normal weight
and overweight groups according to their BMI. The participants had no musculoskeletal
disorders and cardiovascular disease. This study was approved by the Research Ethics
Committee, Mahidol University, Thailand. The participants signed in the informed consent
prior to data collection.
Anthropometric measurement and physical assessment for each participant were
carried out as follows: weight and height by using weight and height scale. After the
anthropometric measurement was complete, trunk muscle performance consisting of
isometric trunk muscle strength and trunk muscle endurance was carried out.
For the trunk muscle strength, each participant was asked to sit on the Biodex chair
(Biodex Corporation, Shirley, NY) with 90 degrees of hip and knee flexion. The
dynamometer axis was aligned with the anterior superior iliac spine level. The participants
performed three maximum isometric of trunk flexion and extension. Consistent verbal
encouragement was given to each participant throughout the testing session. In addition,
each participant was required to look at the Biodex monitor during testing for the visual
feedback.
For the trunk muscle endurance, each participant was required to take part in four
trunk muscle endurance tests. For the trunk extensor muscle endurance test, each participant
was ask to lay prone on the testing table and then move the upper body out of the table with
resting their arms and upper body on a trunk supporter. The lower body was fixed with the
table by using cloth straps around the pelvis, knee and ankle. A feedback pad was placed
over the area between both scapulae. When the test started, the participant crossed their
arms and maintained the unsupported trunk in the horizontal position as long as possible.
The test terminated when the participant was unable to maintain that position. For the trunk
flexor muscle endurance test, the participant was in crook lying position on the testing table.
The upper body was supported by the wedge board set in 45 degrees from the table. The
hips and knees were bent 90 degrees. The participant crossed the arms on the chest. The
feedback pad was set to place on the participant’s sternum. When the test started, the
participant was required to maintain this position as long as possible. The wedge board was
moved away from the participant’s back. The test was terminated when the participant was
unable to maintain the upper body at 45 degrees leaning backward. For the trunk side
bridge endurance test, the participant lay on the right side with the head placing on a pillow
and arms on the upper limb supporter. The legs were kept extended with placing the left
foot in front of the right one. A feedback pad was placed over the left iliac crest to monitor
the participant’s position. When the test started, the participant lifted the hip up from the
table and maintained this position as long as possible. The test was terminated when the
participant was unable to maintain the hip in this position.
Statistical Package for Social Sciences (SPSS) version 19.0 was used for data
analysis. The independent sample t-test was used to compare all of trunk muscle strength
and endurance mean between two groups.
Results
Peak torque of trunk muscle strength (Nm) and trunk muscle endurance time (second)
were analyzed by independent sample t-test.
Trunk muscle strength
Mean, standard deviation, minimal and maximum values of trunk muscle strength in
normal weight and overweight groups are presented in Table 1. For the trunk extensor
muscle strength, the results showed no significant difference in peak torque for normal
weight and overweight groups; t(58)=1.653; p=0.104. For the trunk flexor muscle strength,
there was no significant difference in peak torque for normal weight and overweight groups;
t(58)=1.24; p=0.22.
Table 1. Mean, standard deviation, minimal and maximum values of trunk muscle strength in normal
weight and overweight females
Strength
Normal weight
Overweight
(Nm)
Mean (SD)
Minimum Maximum
Mean (SD)
Minimum Maximum
Extension
134.2 (29.8)
76.1
206.0
148.7 (37.7)
88.7
233.6
Flexion
87.9 (26.6)
52.7
168.0
97.1 (30.9)
56.0
170.0
Trunk muscle endurance
Mean, standard deviation, minimal and maximum values of trunk muscle endurance
time in the normal weight and overweight groups are presented in Table 2. The results
showed that the normal weight group had significantly longer mean extensor endurance time
than that in overweight group (t(58)=4.249; p<0.001). Moreover, for the trunk flexion
endurance, the normal weight group also had significantly longer endurance time than that in
overweight group (t(58)=3.476; p=0.001). For the side bridge endurance test, no significant
difference in the endurance time was found between the normal weight and overweight
groups for both right (t(58)=0.033; p=0.973) and left (t(58)=0.234; p=0.816) sides. The
comparison of trunk muscle endurance time between the normal weight and overweight
females was presented in Figure 1.
Table 2. Mean, standard deviation, minimal and maximum values of trunk muscle endurance time in normal
weight and overweight females
Endurance time
Normal weight
Overweight
(second)
Mean (SD)
Minimum Maximum
Mean (SD)
Minimum Maximum
Extension
126.1 (26.7)
90.7
193.4
86.2 (44.0)
17.8
240.0
Flexion
118.6 (24.8)
49.9
179.0
83.0 (50.4)
32.7
240.0
Right side bridge
79.0 (45.2)
29.1
240.0
78.6 (47.8)
20.3
240.0
Left side bridge
68.3 (38.5)
29.1
177.2
66.2 (28.3)
17.9
135.9
Figure 1. Comparison of trunk muscle endurance time between normal weight and overweight females
Trunk muscle endurance time (second)
140
**
*
120
100
80
60
Normal weight
40
Overweight
20
0
Extension
Flexion
Right side
bridge
Left side bridge
** Statistical significance at p < 0.001
* Statistical significance at p < 0.05
Discussion and Conclusion
This study aimed to compare the trunk muscle strength and endurance between the
normal weight and overweight females. This is the first study to investigate such
comparisons. The findings showed that the trunk muscle strength between both groups was
not significantly different, whereas the trunk muscle endurance between both groups was
significantly different.
Regarding the strength, stronger trunk extensor and flexor muscle strength was
reported in previous studies (24, 25). The findings obtained from the present study did not
seem to correspond with other previous studies. Despite non-significant results between both
groups, the overweight group tended to have stronger trunk muscles than the normal weight
one.
A few plausible reasons why the trunk extensor and flexor muscle strength of
overweight group was not significantly different from that of normal weight group in this
study. First, it might be differences in the criteria of BMI for classifying the participants
among studies. The BMI criteria to classify normal weight and overweight level used in this
study relied on the following Asian population: 18.0-22.9 kg/m2 vs 23.0-24.9 kg/m2 for the
normal weight and overweight groups, respectively (3, 4). In contrast, such BMI criteria used
in the previous studies (13) relied on the WHO criteria: 18.0-24.9 kg/m2 vs 25.0-29.9 kg/m2
(2). In this study, the participants’ mean BMI for the normal weight was 20.6 kg/m2 and for
the overweight 23.9 kg/m2. The participants’ minimum BMI of the overweight group is close
to maximum limit of normal weight females, in other words, borderline groups each
participant was classified.
Second, it might be that the methods employed to measure muscle strength accounted
for different findings. The participants in this study performed the isometric test while those
in the previous studies performed isokinetic test. The gravity has an effect on trunk muscle
strength when measuring by the isokinetic strength test (25), while the gravity has no effect
on the strength when measuring by the isometric test.
In addition, there were some body mass-related factors contributing the overweight
females to produce more strength, compared to the normal weight females. For example, it
would be advantageous for the overweight females to use their body weight to help exert
more forces. Some previous studies attributed prolonged training effect on trunk muscles to
support the large body mass (14) and on lower extremities (26) to more strength in the
overweight persons. Such training effect may lead to muscle mass adaptation and generate
greater force output.
Regarding the endurance, the results showed longest trunk extensor muscles
endurance time, compared to the trunk flexor and side bridge muscles. This finding was in
accordance with those of previous studies conducted by Ito (27) and Thong-on (22). In
contrast to the findings of some previous studies (20, 21) which reported longest trunk flexor
muscle endurance time among trunk extensor and side bridge muscles.
In addition, regarding the comparisons between the normal weight and overweight
females, a few previous studies were conducted to investigate the trunk muscle endurance in
obese persons (19, 24). The results from the present study correspond with those from
previous studies, that is, the non-obese persons have more endurance of trunk muscles than
the obese persons (24). Two possible reasons were proposed. First, fatigue perception,
which implied endurance, of the normal weight persons was higher than obese persons (24).
Second, the obese persons have more lumbar lordosis and anterior pelvic tilt than the nonobese persons. The anterior pelvic tilt was shown to have sacroiliac joint flexion and
increased shear force on lower lumbar spine (28).
The findings from this study would imply that despite seemingly more strength found
in the overweight females, such people tend to get benefit to exert force in short time.
However, their muscles may not be able to endure prolonged contraction. In addition, the
overweight persons tend to have poor lumbopelvic muscle control which contribute to
instability of the lumbar spine.
There is some limitation in this study. This study tested the trunk muscle strength in
isometric tests which the results may not be comparable with those from other studies using
isokinetic tests.
In conclusion, this study demonstrated the trunk muscle strength and endurance in the
normal weight and overweight females. The isometric trunk muscle strength in the normal
weight females did not differ from that in the overweight ones. The extensor and flexor
muscle endurance times in the normal weight females were longer than those in the
overweight females. These results can be applied to design for appropriate exercise program
for normal weight and overweight females.
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Acknowledgements: I would like to express my sincere gratitude to Ms Penpailin Eakudchariya and Mr Pipat Suwiwattanasirikul for their kind assistance during data collection
process.