Analysis of the Relationship between Obesity Factors and Health-Related Physical Fitness Factors among People with Intellectual Disabilities in South Korea

Abstract

Little is known about the relationship between health-related physical fitness factors and obesity-related factors in individuals with intellectual disabilities. We investigated the prevalence of obesity and the relationship between obesity-related factors and health-related physical fitness factors among people with intellectual disabilities in South Korea to identify the physical fitness factors that influence the degree of obesity. For obesity-related factors, we measured body composition (height, weight, body mass index—BMI, and body fat percentage) of 108 subjects with intellectual disabilities (mean ± standard deviation; age = 24.4 ± 8.45 years). For health-related physical fitness factors, we measured muscular strength, muscular endurance, and flexibility. There was a significant negative correlation between muscular endurance and obesity factors (BMI, r = −0.306, p < 0.01; body fat percentage, r = −0.402, p < 0.01). Further, the prevalence of obesity (34.3%) and being overweight (17.6%) among people with intellectual disabilities was high in South Korea. In addition, muscular endurance was found to have a significant effect on the obesity level (β = −0.239, p < 0.000). This suggests that a program that considers muscular endurance should be prioritized when implementing an exercise intervention strategy for the treatment of overweight and obesity among people with intellectual disabilities.

Full text

International Journal of
Environmental Research
and Public Health
Article
Analysis of the Relationship between Obesity Factors and
Health-Related Physical Fitness Factors among People with
Intellectual Disabilities in South Korea
Guyeol Jeong 1and Buongo Chun 2, *


Citation: Jeong, G.; Chun, B.
Analysis of the Relationship between
Obesity Factors and Health-Related
Physical Fitness Factors among
People with Intellectual Disabilities in
South Korea. Int. J. Environ. Res.
Public Health 2021,18, 6533.
https://doi.org/10.3390/
ijerph18126533
Academic Editor: Sylvia Kirchengast
Received: 16 April 2021
Accepted: 14 June 2021
Published: 17 June 2021
Publisher’s Note: MDPI stays neutral
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Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
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Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
1Department of Social Physical Education, College of Humanities and Arts, Sunchon National University,
Sunchon 57922, Korea; zzzinsang@hanmail.net
2Graduate School of Physical Education, College of Arts and Physical Education, Myongji University,
Yongin 17058, Korea
*Correspondence: tianbingwu@mju.ac.kr; Tel.: +82-(31)-330-6302
Abstract:
Little is known about the relationship between health-related physical fitness factors and
obesity-related factors in individuals with intellectual disabilities. We investigated the prevalence of
obesity and the relationship between obesity-related factors and health-related physical fitness factors
among people with intellectual disabilities in South Korea to identify the physical fitness factors that
influence the degree of obesity. For obesity-related factors, we measured body composition (height,
weight, body mass index—BMI, and body fat percentage) of 108 subjects with intellectual disabilities
(mean
±
standard deviation; age = 24.4
±
8.45 years). For health-related physical fitness factors, we
measured muscular strength, muscular endurance, and flexibility. There was a significant negative
correlation between muscular endurance and obesity factors (BMI, r=
−
0.306, p< 0.01; body fat
percentage, r=
−
0.402, p<0.01). Further, the prevalence of obesity (34.3%) and being overweight
(17.6%) among people with intellectual disabilities was high in South Korea. In addition, muscular
endurance was found to have a significant effect on the obesity level (
β
=
−
0.239,
p< 0.000
). This
suggests that a program that considers muscular endurance should be prioritized when implementing
an exercise intervention strategy for the treatment of overweight and obesity among people with
intellectual disabilities.
Keywords:
people with intellectual disability; overweight; obesity; health-related physical fitness
factor; muscular endurance; relationship
1. Introduction
Obesity is a complex chronic disease characterized by excessive accumulation of body
fat. It has been declared a global pandemic by the World Health Organization (WHO) [
1
].
Its prevalence is high among children, adolescents, and adults in developed countries [
2
].
Obesity is considered a dangerous disease because it causes or worsens many health
problems independently or in connection with other diseases. The WHO defines obesity
as body mass index (weight—kg divided by the square of height—m
2
; body mass index—
BMI) of over 30 kg/m
2
[
3
,
4
]. Among Asians, obesity is defined as a BMI of
≥
25 kg/m
2
[
5
].
BMI is a person’s weight in kilograms divided by the square of height in meters. BMI is
an inexpensive and easy screening method for weight categories, such as underweight,
healthy weight, overweight, and obesity. Obesity has negative effects on health, such as
type 2 diabetes, hypertension, cardiovascular disease, and premature death. It is also highly
related to social and psychological problems as well as a social and economic burden [
6
–
9
].
Since such obesity-related costs impose a large economic burden on society [
10
], rapid
intervention and treatment for obesity are required.
In particular, it has been reported that the prevalence of obesity is higher among
people with intellectual disabilities than among the general population [
11
–
13
]. According
Int. J. Environ. Res. Public Health 2021,18, 6533. https://doi.org/10.3390/ijerph18126533 https://www.mdpi.com/journal/ijerph

Int. J. Environ. Res. Public Health 2021,18, 6533 2 of 11
to a study on people with intellectual disabilities in Australia, the prevalence of obesity
(23.8%) and being overweight (22.5%) was higher in this population than that in the general
population [
12
]. In the UK, the prevalence of obesity and being overweight among adults
with intellectual disabilities is 20.7% and 28%, respectively [
11
]. This indicates that obesity
is a more serious problem among people with intellectual disabilities than among the
general population [14,15].
On the other hand, it has been reported that the number of people with intellectual
disabilities is the highest in low- and middle-income countries [
16
]. Currently, there
are
2.59 million
people with disabilities in South Korea, accounting for 5% of the total
population, of which 212,936 have intellectual disabilities. The proportion of people with
intellectual disabilities among the population with disabilities consistently increased from
6.9% in 2009 to 8.2% in 2015, to 9.0% in 2018 [
17
]. Although it may seem that the prevalence
of being overweight and obese among people with intellectual disabilities is higher in
South Korea than in Western countries due to social and environmental problems, studies
examining such prevalence are limited.
Obesity is caused by a variety of factors, including environmental and genetic fac-
tors [
18
]. In particular, it has been reported that decreased physical activity, decreased
physical fitness, inadequate nutritional intake, and a sedentary lifestyle are risk factors of
obesity [
19
]. In this regard, people with intellectual disabilities are limited in their physical
activities due to limitations in language development, cognitive function, and cognitive
impairment [
20
]. It has also been reported that many of them lead a sedentary lifestyle [
21
].
In addition, as they have a stronger desire for food intake than the general population, the
prevalence of obesity is also higher [
22
]. Their lack of physical activity leads to a decline in
their fitness level, which, in turn, causes various diseases such as obesity, hypertension,
type 2 diabetes, and cardiovascular disease, thereby decreasing the health of people with
intellectual disabilities [
23
]. Previous studies have shown that people with low fitness
levels have a higher risk of becoming overweight or obese than those with high fitness
levels [
24
,
25
]. Other studies have also shown that obese or overweight individuals have
lower physical fitness levels than do people with a normal weight [
26
], and that physical
fitness and body fat are negatively correlated [27].
It can be assumed that higher physical fitness levels among people with intellectual
disabilities are associated with better body composition. However, little is known about
the relationship between health-related physical fitness factors and obesity-related factors
in this population. In addition, while the prevalence of intellectual disabilities and obesity
is increasing in middle-income countries such as South Korea, no survey data have been
reported on the obesity rates of teenagers to adults in their 40 s or the relationship between
obesity and health-related physical fitness factors. Therefore, we aimed to investigate
the prevalence of obesity among people with intellectual disabilities in South Korea and
examine the relationship between health-related physical fitness and obesity-related fac-
tors. Elucidating the physical factors associated with obesity in people with intellectual
disabilities could lead to the development of new intervention programs to promote a
healthier lifestyle in this population. Our results can help researchers, clinical experts, and
trainers develop intervention strategies for the treatment of obesity and further motivate
policymakers and decision makers to prioritize the treatment of people with intellectual
disabilities.
2. Materials and Methods
2.1. Subjects
In total, 108 individuals with intellectual disabilities (75 men and 33 women) residing
in City G in South Korea were included in this study. They were selected from people with
intellectual disabilities who visited the Physical Fitness Certification Center for the Disabled
in City G (https://nfa.koreanpc.kr/front/centerpop/bs/boardList.do?center_cd=002&
board_seq=14&type=popup, accessed on 23 January 2019). The inclusion criteria for
subjects in this study are as follows: (1) participants, parents, and/or legal guardians have

Int. J. Environ. Res. Public Health 2021,18, 6533 3 of 11
signed prior consent before participation; (2) people who can walk without help;
(3) people
without motor impairment. The exclusion criteria for the subjects in this study are as
follows: (1) people who are prohibited from exercising; (2) persons with a physical disability
who are unable to perform physical activities. After we provided a thorough explanation of
the purpose of our study and the measurement method to the visitors and their guardians
in accordance with the Ethical Principles of the Declaration of Helsinki, we selected subjects
among those who gave consent. In addition, for the sake of consistency, measurement and
evaluation experts at the Physical Fitness Certification Center for the Disabled performed
the measurements. Table 1shows the general characteristics of the participants.
Table 1. Subject characteristics.
Variables Total (N= 108) Male (n= 75) Female (n= 33)
Age 24.40 ±8.45 24.99 ±7.92 23.06 ±9.56
Height (cm) 163.97 ±9.48 166.88 ±8.66 157.34 ±7.87
Weight (kg) 63.67 ±14.61 64.38 ±14.71 62.06 ±14.48
BMI (kg/m2)23.62 ±4.97 22.98 ±4.43 25.08 ±5.82
% Body fat (%) 27.94 ±10.46 24.24 ±8.41 36.62 ±9.71
Data are presented as the mean ±standard deviation. BMI, body mass index.
2.2. Measurement
The health-related physical fitness of people with intellectual disabilities who partici-
pated in this study was measured using measuring instruments available at the Physical
Fitness Certification Center for the Disabled in City G. As for the measurement criteria,
body composition (height, weight, BMI, and body fat percentage), muscular strength,
muscular endurance, and flexibility were measured.
Body Composition
The height (cm), weight (kg), BMI, and body fat percentage of subjects with intellectual
disabilities were measured using an automatic height–weight scale (BSM 330, Inbody, Seoul,
Republic of Korea) and bioelectric impedance analysis (InBody 770, InBody, Seoul, Republic
of Korea) [
28
]. BMI was calculated by dividing the weight in kilograms by the height in
meters. Participants were classified as normal weight (BMI < 23), overweight (
BMI ≥23
),
and obese (BMI
≥
25) [
5
]. Obesity was defined as BMI
≥
25 kg/m
2
according to the
Asia Pacific standards of the WHO guidelines [
5
]. The method of measuring the body
composition required the subjects to wear light clothing (exercise clothing) and to place the
soles of their bare feet evenly on the footing. Standing in an upright position facing the
front, holding the grip with both hands, and opening the gap between the armpits. When
the machine scans the body, it is measured while keeping the body immobile [
29
]. For
accurate measurements, we asked the subjects to change into clothing that was as simple
as possible, to remove any substances attached to the body, and to take measurements an
hour after emptying their bowels.
2.3. Health-Related Physical Fitness
Health-related physical fitness was measured using variables included in the physical
fitness criteria for people with intellectual disabilities at the Physical Fitness Certification
Center for the Disabled. Before measuring physical fitness, simple warm-up exercises and
stretching were performed for approximately five minutes with the help of measurement
and evaluation experts. The following sections describe the measurement methods for
each criterion.
2.3.1. Muscular Strength
Muscular strength was measured by using a grip strength dynamometer (BS-HG,
Inbody, Seoul, Korea) [
30
–
32
]. For the measurement method, the subject needed to stand
shoulder-width apart, and hold the grip while the body and arms are stretched out, about

Int. J. Environ. Res. Public Health 2021,18, 6533 4 of 11
15 degrees apart. The measurement was made with a maximum pull of over two to
three seconds from the start of the measurement. In cases where people with intellectual
disabilities could not hold the instrument firmly, assistants helped them to grip and exert
maximum force and maintain it for five seconds. Muscular strength was measured twice
and was recorded in units of 0.1 kg of the highest value.
2.3.2. Muscular Endurance
The sit-up test was used to measure muscular endurance (BS-SU, Inbody, Seoul,
Republic of Korea) [
33
,
34
]. Prior to the measurement of muscular endurance, we asked
subjects to do the following: (1) lie on their head and back, on the mattress; (2) place their
knees at a 45
◦
angle and make a gap between them, such that it fits into a fist; (3) perform
sit-ups for a minute while clasping both hands behind their head. The two elbows were to
touch the knees and then return to their initial positions once. The unit of measurement for
muscular endurance was the number of repetitions per 30 s. In order to help people with
intellectual disabilities understand the procedure, we let them practice two to three times
with the help of assistants and we informed them of the number of repetitions during the
measurement.
2.3.3. Flexibility
Flexibility was measured using sit-and-reach exercises by a buckling flexion meter (BS-
FF, Inbody, Seoul, Korea) [
34
,
35
]. Subjects were asked to take their shoes off and straighten
their legs so that both heels were in close contact with the measurement instrument, then
overlap their hands, and extend their arms forward. The upper body was bent as far as
possible to push out the ruler. We took the measurement twice and selected the highest
value. If a subject could not stretch their knees because of having a low cognitive ability due
to an intellectual disability, an assistant pressed the knee of the subject to prevent it from
bending and provided a demonstration to prevent the pushing of the lateral flexometer
measurement plate due to recoil.
2.4. Data Analysis
We calculated the mean (M) and standard deviation (SD) for each criterion using
the Statistical Package for the Social Sciences version 22 (IBM Corp., Armonk, NY, USA).
A frequency
analysis was performed to explain the general characteristics of the subjects.
Further, a cross-analysis was conducted to examine the ratio of obesity and being over-
weight according to the sex and age group. Pearson’s correlation analysis was conducted
to examine the relationship between obesity-related factors (BMI, body fat percentage)
and health-related physical fitness factors (muscular strength, muscular endurance, and
flexibility). Multiple regression analysis was conducted to examine which variables affected
the degree of obesity. The statistical significance level was set at p< 0.05.
3. Results
3.1. Analysis of Obesity Severity According to the Sex of People with Intellectual Disabilities
The analysis of obesity severity according to sex among people with intellectual
disabilities is shown in Figure 1. The prevalence of obesity (according to BMI) among
people with intellectual disabilities was 34.3%. There was no significant difference between
men (34.7%) and women (33.3%). According to BMI, the ratio of being overweight among
people with intellectual disabilities was 17.6% (19 people). Although female subjects
(21.2%; 7 people) showed a higher ratio than male subjects (16.0%; 12 people), there was no
significant difference (x2= 0.0.437; p= 0.804). According to BMI, the proportion of people
with intellectual disabilities that belong to the normal weight range was 48.1% (52 people).
There was no significant difference between male (49.3%; 37 people) and female (45.5%;
15 people) subjects.

Int. J. Environ. Res. Public Health 2021,18, 6533 5 of 11
Figure 1.
Percentages of Koreans in this study with intellectual disabilities who have a normal weight, are overweight,
and obese: (
a
) percentage of overweight and obese (total subjects (N= 108)); (
b
) percentage of overweight and obese male
subjects (n= 75); (c) percentage of overweight and obese female subjects (n= 33).
3.2. Analysis of Obesity Severity According to Age among People with Intellectual Disabilities
The analysis of obesity severity according to the age group of people with intellectual
disabilities is summarized in Table 2. The prevalence of obesity tended to increase with
age: the prevalence was 19.4% in people aged 10–19 years old (6 people), 35.7% (20 people)
in subjects aged 20–29 years old, 38.5% (5 people) in subjects aged 30–39 years old, and 75%
(6 people) in subjects aged 40–49 years old. However, there was no significant difference
between age groups. The proportion of overweight subjects was 12.9% (4 people) in
the
10–19 age
group, 19.6% (11 people) in the 20–29 age group, 23.1% (3 people) in the
30–39 age
group, and 12.5% (1 person) in the 40–49 age group. The proportion of subjects
that belonged to the normal weight range was 67.7% (21 people) in the 10–19 age group,
44.6% (25 people) in the 20–29 age group, 38.5% (5 people) in the 30–39 age group, and
12.5% (1 person) in the 40–49 age group. There was no significant difference between
the age groups. In addition, the basic characteristics (age, height, and weight) of the
participants, obesity-related factors (BMI and % body fat), and health-related fitness factors
(sit-up, sit and reach, and grip strength) are shown in Table 3.
Table 2.
Frequency analysis of obesity level by age group in participants with intellectual disabilities.
Variables Age 10–19
(n= 31)
Age 20–29
(n= 56)
Age 30–39
(n= 13)
Age 40–49
(n= 8) x2
Normal 21 (67.7%) 25 (44.6%) 5 (38.5%) 1 (12.5%) 11.829
(p= 0.066)
Overweight 4 (12.9%) 11 (19.6%) 3 (23.1%) 1 (12.5%)
Obese 6 (19.4%) 20 (35.7%) 5 (38.5%) 6 (75.0%)
Data are presented as frequency (percentage); x2= Chi-square.
Table 3. Descriptive statistics for the whole study cohort (n= 108).
Variables nMean SD SE Min Max Range 95%CI
Age 108 24.38 8.49 0.82 12.00 46.00 34.00 (22.76; 26.01)
Height (cm) 108 164.13 9.36 0.91 135.50 187.20 51.70 (162.34; 165.93)
Weight (kg) 108 63.59 14.66 1.42 33.20 108.90 75.70 (60.78; 66.40)
BMI (kg/m2)108 23.53 4.89 0.47 15.22 39.33 24.11 (22.59; 24.46)
% Body fat (%) 108 27.94 4.89 1.01 7.60 58.30 50.70 (22.59; 24.46)
Sit-up 108 22.22 9.52 0.92 5.00 59.00 54.00 (20.40; 24.05)
Sit and reach 108 0.21 11.94 1.15 −30.00 23.20 53.20 (−2.08; 2.50)
Grip strength 108 20.66 8.73 0.84 6.40 43.30 36.90 (18.99; 22.33)
SD, standard deviation; SE, standard error; Min, minimum; Max, maximum; CI, confidence interval; BMI, body mass index.

Int. J. Environ. Res. Public Health 2021,18, 6533 6 of 11
3.3. Correlation between Factors among People with Intellectual Disabilities
Table 4shows the results of the correlation analysis between age, body composition,
and health-related physical fitness factors of people with intellectual disabilities. Weight
showed positive correlations with age (r = 0.309, p< 0.01) and height (r = 0.459, p< 0.01);
BMI showed positive correlations with age (r = 0.275, p< 0.01) and weight (r = 0.873,
p< 0.01).
Table 4.
Correlation analysis among age, body composition, and health-related physical fitness in people with
intellectual disabilities.
Variables Age Height Weight BMI Body Fat
Percentage Sit-Up Sit and Reach Grip
Strength
Age 1
Height 0.160 1
Weight 0.309 ** 0.459 ** 1
BMI 0.275 ** −0.021 0.873 ** 1
Body fat percentage
0.162 −0.263 ** 0.560 ** 0.789 ** 1
Sit-up −0.282 ** 0.045 −0.222 * −0.306 ** −0.402 ** 1
Sit and reach −0.014 −0.132 −0.162 −0.110 −0.120 0.285 ** 1
Grip strength 0.270 ** 0.386 ** 0.235 * 0.028 −0.173 0.318 ** 0.312 ** 1
BMI, body mass index; *, p> 0.05; **, p> 0.01.
Body fat percentage was negatively correlated with height (r=
−
0.263, p< 0.01) and
positively correlated with weight (r= 0.560, p< 0.01) and BMI (r= 0.789, p< 0.01). Sit-ups
showed a negative correlation with age (r=
−
0.282, p< 0.01), weight (r=
−
0.222,
p< 0.05
),
BMI (r=
−
0.306, p< 0.01), and body fat percentage (r=
−
0.402, p< 0.01) (Figure 2). Sit
and reach was positively correlated with sit-ups (r= 0.285, p< 0.01). Grip strength was
positively correlated with age (r= 0.270, p< 0.01), height (r= 386, p< 0.01), weight (
r= 0.235
,
p< 0.05), sit-ups (r= 0.318, p< 0.01), and sit and reach (r= 0.312, p< 0.01).
Figure 2.
The relationship between body fat and muscular endurance (sit-ups) among Korean
participants with intellectual disability. Body fat percentage is negatively correlated with sit-ups
(r=−0.402, p< 0.001).
3.4. Factors Affecting the Body Fat Percentage of People with Intellectual Disabilities
To examine the factors associated with body fat percentage, which had the highest
significant correlation with the obesity level of people with intellectual disabilities, we

Int. J. Environ. Res. Public Health 2021,18, 6533 7 of 11
performed multiple regression analysis (Table 5). When we analyzed the effects of height,
weight, and sit-up factors (which showed significant correlations with body fat percentage)
on body fat percentage, we found that their explanatory power (R2) was 72.5% and that
the results were statistically significant (F = 90.361, p<0.001). In addition, we tested
the significance of each factor and found that height (p< 0.001), weight (p< 0.001), and
sit-ups (p< 0.001) had significant effects on body fat percentage. In order to determine the
importance of the factors influencing body fat percentage, we compared the standardized
regression coefficients (
β
values) and found that height (
β
=
−
0.735), weight (
β
= 0.591),
and sit-ups (β=−0.239) had an effect on body fat percentage in decreasing order.
Table 5. Factors affecting body fat percentage.
Variables Non-Standardized Coefficients Standardized Coefficients tpVIF
B SE β
Constant 116.28 9.833 11.825 0.000
Height −0.735 0.066 −0.658 −11.078 0.000 1.319
Weight 0.591 0.043 0.828 13.616 0.000 1.383
Sit-up −0.239 0.059 −0.218 −4.075 0.000 1.067
R = 0.851, R
2
= 0.725, F = 90.361, p= 0.000; B, unstandardized beta coefficient; SE, standard error;
β
, standarded beta coefficient; VIF, variance
inflation factor.
4. Discussion
Our study aimed to investigate the prevalence of obesity and physical fitness fac-
tors affecting obesity among people with intellectual disabilities in South Korea. Our
results show a high prevalence of overweight and obesity among people with intellectual
disabilities in South Korea. The prevalence of overweight and obesity among people
with intellectual disabilities was similar between male and female subjects. This shows
a tendency to increase with age. In addition, there was a significant correlation between
health-related physical fitness factors (muscular endurance) and obesity factors (BMI and
body fat percentage) among people with intellectual disabilities in South Korea. Moreover,
the muscular endurance factor had a significant effect on the body fat percentage (
Figure 2
).
Obesity is a negative body change that degrades the quality of human life, regardless of
the presence or absence of a disability, and requires continuousand systematic management.
As people with intellectual disabilities tend to have low levels of physical activity and
indulge in excessive nutritional intake, they are prone to having an unbalanced body, being
overweight, and having impaired body functions, which eventually leads to obesity [28].
The prevalence rates of overweight (17.6%) and obesity (34.3%) among people with
intellectual disabilities in this study were similar to those of other countries. For example,
in an Australian study of 206 subjects, approximately 22.5% of subjects were obese, and
23.8% were overweight [
12
]. A study in the UK also reported that the prevalence rates
of obesity and overweight were 20.7% and 28.0%, respectively, whereas subjects that fell
in the normal range of weight accounted for 32.7% [
11
]; a study by Hsieh et al. [
36
] on
people with intellectual disabilities in the United States reported prevalence rates of 28.9%
for overweight and 38.3% for obesity. The prevalence of overweight and obesity is higher
among people with intellectual disabilities than in the general population [
12
,
13
,
37
,
38
].
This may be because people with intellectual disabilities have decreased income levels in
an environment where they have difficulty engaging in economic activities, which leads to
a lack of opportunities to participate in physical activities and exercise programs [
20
,
39
].
At this rate, obesity among people with intellectual disabilities is expected to increase
more rapidly in the future, thereby increasing the morbidity rate as well. Therefore, it
is necessary to pay closer attention to obesity treatment interventions for people with
intellectual disabilities.
In our study, there was no significant difference between the ratio of being overweight
(male 16.0% vs. female 21.2%) and the prevalence of obesity (male 34.7% vs. female
33.3%) according to sex. This is supported by a meta-analysis on adults with intellectual

Int. J. Environ. Res. Public Health 2021,18, 6533 8 of 11
disabilities, which showed no difference in sedentary behavior between genders [
40
].
However, it is necessary to prioritize interventions for women with intellectual disabilities,
given that the following studies: the study in [
40
] showed a significantly lower physical
activity level in female, compared with male, subjects with intellectual disabilities, and
Hsieh et al. [
36
] suggested that women have a higher risk of becoming severely obese than
men with intellectual disabilities.
It has been reported that overweight and obese people have lower physical fitness
than those with normal weight. However, to the best of our knowledge, few studies have
analyzed the relationship between health-related physical fitness factors and obesity factors
among people with intellectual disabilities. Our results showed an inverse relationship
between muscular endurance and BMI as well as the body fat percentage of people with
intellectual disabilities (BMI, r=
−
0.306; body fat percentage, r=
−
0.402). In addition,
through multiple regression analysis, we found that muscular endurance had a significant
effect on body fat percentage among people with intellectual disabilities (
β
=
−
0.218,
p= 0.000).
Although it is difficult to make a direct comparison, several studies on people without
disabilities have shown a negative relationship between obesity factors and physical
fitness [
26
,
27
,
41
,
42
]. A previous study by Fogelholm et al. [
27
] in normal adolescents
showed a strong negative relationship between muscular endurance (sit-ups) and being
overweight. A similar result was found in a study by Lee and Oh [
43
], who examined
male Korean adolescent subjects without disabilities (n= 3047) and found that muscular
endurance is a significant factor affecting obesity. These results suggest that exercise
programs that improve muscular endurance should be considered during interventions for
people with intellectual disabilities who are overweight and obese.
Muscular endurance refers to the ability to use the muscles continuously for a certain
period of time [
44
] and can be improved by strength training. The exercise method that can
improve muscular endurance in a population with a low physical fitness level is as follows:
perform 10–15 repetitions of an exercise with an intensity of one repetition maximum
of 40–50% or less, one to two sets per muscle area, and with short breaks between each
set [
44
–
46
]. Although aerobic exercise for cardiorespiratory fitness may be important for
people with intellectual disabilities, it may be wise to focus instead on improving muscular
endurance, because low muscular endurance can limit aerobic exercise performance [47].
Meanwhile, muscular strength and flexibility were not shown to significantly af-
fect obesity-related factors in intellectually disabled people. These results are similar to
those of previous studies, which found a static correlation between weight and muscle
strength
[48,49]
. Muscular strength is defined as the ability of a muscle to exert maximum
contractile force at once, against resistance [
50
–
52
]. Muscular strength can be important
for everyday life, in intellectually disabled people [
53
,
54
]. However, our results suggest
that muscular strength is the next consideration in exercise programs to mediate obesity.
Regarding flexibility, many previous studies have reported no significant association with
obesity [
55
–
57
]. Although flexibility does not significantly affect obesity factors, it is be-
lieved that some participation in exercise could help in the daily lives of intellectually
disabled people. This is because lack of flexibility is associated with musculoskeletal
damage and back pain [55,58].
Given the small sample size of our study, it is difficult to generalize our results. Future
research should include a larger number of subjects and investigate the relationship and
determinants of various obesity-related physical fitness factors in order to promote health
among people with intellectual disabilities.
5. Conclusions
Our results show an inverse relationship between muscular endurance and obesity
factors among people with intellectual disabilities in South Korea. In addition, muscular
endurance factors were found to have a significant effect on the body fat percentage
in this population. This suggests that a program that takes muscular endurance into

Int. J. Environ. Res. Public Health 2021,18, 6533 9 of 11
account should be considered when implementing an exercise intervention strategy for
the treatment of overweight and obesity among people with intellectual disabilities. In
addition, we confirmed, though with a small sample size, that the prevalence of overweight
and obesity in Korean people with intellectual disability may be relatively high. It will
be necessary to determine the continued prevalence of obesity by adding the number of
cases in the future. Since an increase in the obesity rate leads to various diseases and is
an important factor that lowers the quality of life of people with disabilities, developing
an effective management method is needed. Our results can help researchers, clinical
experts, and trainers develop intervention strategies for the treatment of obesity and
further motivate policymakers and decision makers to prioritize the treatment of people
with intellectual disabilities.
Author Contributions:
Conceptualization, G.J. and B.C.; methodology, B.C.; software, B.C.;
validation
,
G.J.; formal analysis, B.C.; investigation, G.J.; resources, G.J.; data curation, G.J.; writing—original
draft preparation, G.J. and B.C. writing—review and editing, B.C.; visualization, G.J.; supervision,
B.C.; project administration, G.J. All authors have read and agreed to the published version of the
manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement:
The study was conducted according to the guidelines of the
Declaration of Helsinki.
Informed Consent Statement:
Informed consent was obtained from all subjects involved in the
study.
Data Availability Statement:
The data that support the findings of this study are available from the
corresponding author, [B.C.], upon reasonable request.
Conflicts of Interest: The authors declare no conflict of interest.
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