Changes in Body Composition and Physical Fitness in Adolescents with Down Syndrome: The UP&DOWN Longitudinal Study

Abstract

Background:

Adolescents with Down syndrome (DS) demonstrate higher values of body composition and lower levels of physical fitness when compared with their peers with typically developing (TD) or their peers with intellectual disability but without DS.

Objective:

To examine, during a 2-year period, changes in indicators of body composition and physical fitness components in TD adolescents and adolescents with DS.

Methods:

Hundred adolescents with DS (64 males) aged 11–20 years old were matched by sex to 163 TD adolescents (108 males) aged 12–18. Indicators of body composition were determined by body mass index (BMI), waist circumference, waist-to-height ratio, skinfolds, and percentage of body fat (%BF). Components of physical fitness were assessed by the Assessing Level of Physical Activity (ALPHA) health-related fitness test battery for youth.

Results:

In the 2-year follow-up, significant (p < 0.05) decreases in BMI and increases in cardiorespiratory fitness and handgrip strength were seen for both groups; decreases in %BF were only seen for participants with DS; and increases in standing long jump were seen only for TD adolescents.

Conclusions:

Results indicate that during the 2-year study period, there were significant decreases in BMI and significant increases in handgrip strength and cardiorespiratory fitness in the TD group. For participants with DS, there was a significant decrease in %BF. However, participants with DS did not exhibit improvements in physical fitness.

Introduction

Obesity is defined as the abnormal or excessive fat accumulation caused by a positive energy balance,¹ which has been associated with a negative impact on health.² The obesity epidemic is the largest public health problem around the world, especially in young people.³ Physical fitness is defined as the ability to perform daily activities without feeling fatigue and comprises a set of physical qualities such as muscular strength, agility, and aerobic capacity.⁴ Physical fitness is considered an important marker of health in youth. There is evidence demonstrating that low levels of physical fitness during adolescence have a negative influence on health status later in life.⁵ Likewise, body composition and levels of physical fitness vary during growth and maturation in the general population,⁶ but limit information about changes of body composition and physical fitness over time is unclear in adolescents with Down syndrome (DS).

DS is a chromosomal disorder occurring every one in 1000 (1/1000) births and it is associated with more than 80 clinical characteristics. Cross-sectional data showed that adolescents with DS present high levels of overweight/obesity and lower levels of physical fitness when compared with typically developing (TD) adolescents and adolescents with intellectual disability but without DS.⁷ Nevertheless, to our knowledge, longitudinal data about change of indicators of body composition and level of physical fitness is scant in this population. Data from the general population demonstrate that significant changes occur in body composition for male and female adolescents, with sex differences.⁶ For example, some indicators of body composition such as body mass index (BMI) increase for males and females but others, such as percentage of body fat (%BF), decrease for males and increase for females.⁶ Regarding components of physical fitness, data showed that adolescents maintained or improved similar values over time in some components (e.g., strength and motor performance) and others declined (e.g., cardiorespiratory fitness) with age.⁸

Therefore, the aim of this study is to examine changes in several indicators of body composition (BMI, waist circumference, waist-to-height ratio, triceps skinfold, subscapular skinfold, and %BF) and components of physical fitness (handgrip strength, standing long jump, motor fitness, and cardiorespiratory fitness) in TD adolescents and adolescents with DS.

Methods

Study Design and Sample

The data collected for this study were part of the UP&DOWN study (study of school children and adolescents with DS: psycho-environmental and genetic determinants of physical activity and its impact on physical fitness, cardiovascular diseases, inflammatory biomarkers, and mental health). Full methodological details of the study were described elsewhere.⁹ The UP&DOWN longitudinal study comprised three repeated observations: (1) Baseline data were obtained between 2011 and 2012, (2) the first follow-up was obtained between 2012 and 2013, and (3) the second follow-up was achieved between 2013 and 2014.

A total of 100 adolescents with DS (64 males) aged 11–20 years old were eligible with baseline data. We also included a sex-matched control group (ratio 1:2) of 163 randomly selected from 673 of TD adolescents aged from 12 to 18 years old recruited into the UP&DOWN study. Adolescents with DS were recruited from special educational schools, associations, and foundations for people with intellectual disabilities in Madrid (Spain) and Toledo (Spain) and TD adolescents were recruited from schools in Madrid (Spain). Adolescents with DS had to meet two essential inclusion requirements for taking part in the study: (1) an intelligence quotient over 35 (relevant institutions provided us with this information before starting the study) and (2) no serious physical disability that could prevent or interfere with physical activity (e.g., wheelchair users or blindness). Written informed consent was obtained from all participants and their parents or guardians before data collection.

The study protocol was approved by the Ethics Committee of the Hospital Puerta de Hierro (Madrid, Spain) and the Bioethics Committee of the National Research Council (Madrid, Spain).

Measures

Assessment of body composition

Body composition variables were obtained by using the following procedures and measured twice, with the average of the two measurements used for data analysis.^10,11

BMI

In terms of weight and height data, participants were measured without shoes and wearing light clothing. An electronic scale (model SECA 701, Hamburg, Germany) to the nearest 0.1 kg was used to measure weight. In terms of height, data were obtained by using a telescopic height-measuring instrument (model SECA 220) to the nearest 1 mm. BMI was calculated by dividing weight by squared height (km/m²). Adolescents were classified into normal or overweight-obesity categories by using the sex- and age-specific cut-off developed by the International Obesity Task Force.¹²

Waist circumference

This was measured over the unclothed abdomen by using the most narrow point between the iliac crest and costal margin with a nonelastic tape (SECA 200; SECA) to the nearest 0.1 cm.¹³

Waist-to-height ratio

It is defined as the ratio of waist circumference to height. It was calculated by dividing the waist circumference by the height of the participant. Distribution of the BF of the participants was obtained.

%BF

This was calculated from skinfold thickness and Slaughter's equations.¹⁴ Triceps and sub-scapular skin fold thickness were measured on the nondominant side of the body to the nearest 0.1 mm with a Holtain caliper at the triceps and sub-scapular sites. %BF was calculated by using Slaughter's equations, which are accurate predictions of BF levels in both populations.¹⁵

Assessment of physical fitness

Fitness was assessed by the ALPHA (Assessing Level of Physical Activity) health-related fitness test battery for youth.¹⁰ More detailed descriptions of each test in adolescents with DS and TD have been reported elsewhere.^9,11

Muscular strength

Upper-body muscular strength was assessed by the handgrip strength test with a hand dynamometer with an adjustable grip (TKK 5101 Grip D; Takey, Tokyo, Japan). Adolescents with DS performed the test in a sitting position to focus their attention on tightening the handgrip, whereas TD adolescents performed in a standing position. This adaptation in the DS population did not show significant differences (p > 0.2) between positions (seated vs. standing) in the handgrip strength scores in TD adolescents in the pilot study.¹¹

Standing long jump test

Lower-body muscular strength was measured by using the standing long jump test. Participants had to jump as far as possible, pushing off vigorously and landing with feet together. The distance was equivalent from the take-off line to the back of the foot on landing.

Motor fitness

Motor fitness was measured by the 4 × 10 m shuttle-run test to assess speed of movement, agility, and coordination. Participants had to run as fast as possible from the start line to the opposite end line and return. In addition, time was multiplied by −1 since a higher score indicated a better motor fitness.

Cardiorespiratory fitness

Cardiorespiratory fitness was assessed by the 20-m shuttle-run test. Participants were required to run between two lines 20 m apart, while keeping pace with a pre-recorded audio CD. The initial speed was 8.5 kmh⁻¹, which was increased by 0.5 kmh⁻¹ each minute (1 minute = one stage). Participants were instructed to run in a straight line, to pivot on completing a shuttle (20 m), and to pace themselves in accordance with the audio signals. The test was finished when the participants failed to reach the end lines concurrent with the audio signals on two consecutive occasions.¹⁶ All adolescents were assessed based on the level of cardiorespiratory fitness recorded in laps.⁹ The 20-m shuttle run has been shown to be a valid and reliable field measurement of cardiorespiratory fitness of youth with DS.¹⁷

All physical fitness tests of the ALPHA health-related physical fitness battery were performed twice, except the 20-m shuttle test, which was performed only once. In the grip strength test, the highest score for each hand was recorded and then the mean score for both hands was calculated. In the standing long jump and motor skills tests, the best attempt was recorded. In addition, to avoid future problems of comprehension of the tests, the instructor showed the adolescents with DS the correct form of execution.

Statistical Analysis

All statistical analyses were performed by using IBM SPSS statistical software package (v.24.0, Chicago, IL) for Macintosh, and the level of significance was set at p < 0.05. Descriptive characteristics of the study sample are presented as means and standard deviations (SDs) or percentages. Paired t-tests were used to examine differences between baseline and each of the follow-up data in body composition and physical fitness variables. A Chi-square test was used to assess differences in the prevalence of overweight/obesity over a 2-years follow-up period. One-way analysis of variance (ANOVA) was used to analyze indicators of body composition and levels of physical fitness by sex groups at baseline and each follow-up. Paired t-test using sex as a covariable was used to analyze body composition and physical fitness variables at baseline and 2-year change.

Also, the tracking of body composition and physical fitness were examined by using Pearson's correlation segmented for sex groups at baseline and follow-ups. Correlations are considered low <0.30, moderate from 0.30 to 0.60, and moderately high >0.60.¹⁸

Results

Descriptive characteristics of study sample at baseline and each follow-up in body composition and physical fitness are shown in Table 1. The 2-year follow-up data demonstrated: (1) For both DS and TD groups, significant increases in BMI, waist circumference, handgrip strength, and cardiorespiratory fitness and significant decreases in %BF; and (2) significant improvements in standing long jump and motor fitness for TD adolescents but not for adolescents with DS.

Table 1.

Descriptive Characteristics of Study Sample at Baseline and Follow-Ups

	n	Baseline	n	1-year follow-up	n	2-year follow-up	p ^*	p ^**
Down syndrome
Age (years)	100	15.7 ± 2.4	100	16.7 ± 2.4	100	17.6 ± 2.5	<0.001	<0.001
Weight (kg)	100	52.0 ± 12.3	100	54.5 ± 12.0	100	56.3 ± 11.7	<0.001	<0.001
Height (cm)	100	147.7 ± 9.5	100	149.5 ± 8.6	100	150.3 ± 8.5	<0.001	<0.001
Body composition
BMI (kg/m²)	100	23.6 ± 4.1	100	24.3 ± 4.3	100	24.8 ± 4.2	<0.001	<0.001
Waist circumference (cm)	100	73.2 ± 9.7	100	74.5 ± 9.4	100	76.5 ± 9.5	0.005	<0.001
Waist-to-height ratio (%)	100	49.6 ± 5.6	100	49.9 ± 5.8	100	51.0 ± 6.0	0.317	<0.001
Triceps skinfold (mm)	100	24.4 ± 10.1	100	19.1 ± 7.2	100	18.1 ± 6.6	<0.001	<0.001
Subscapular skinfold (mm)	100	20.4 ± 9.8	100	20.1 ± 8.6	100	20.4 ± 11.1	0.644	0.975
BF (%)	100	34.2 ± 12.8	100	31.0 ± 11.2	100	30.6 ± 11.6	0.001	0.002
Overweight/obesity (%)	100	36	100	46	100	47	0.798	0.227
Physical fitness
Handgrip strength (kg)	100	15.9 ± 6.6	100	17.4 ± 5.9	100	17.9 ± 6.9	0.020	<0.001
Standing long jump (cm)	100	74.4 ± 38.0	100	73.5 ± 34.7	100	77.0 ± 32.3	0.720	0.308
Motor fitness (sec)^a	100	−19.2 ± 4.5	100	−20.1 ± 4.8	100	−18.9 ± 4.4	0.005	0.062
Cardiorespiratory fitness (laps)	100	8.3 ± 5.9	100	9.3 ± 6.9	100	10.1 ± 6.8	0.034	<0.001
Typically developing
Age (years)	163	13.8 ± 1.4	163	14.7 ± 1.4	163	15.7 ± 1.4	<0.001	<0.001
Weight (kg)	163	54.9 ± 11.9	163	59.1 ± 11.5	163	62.8 ± 11.4	<0.001	<0.001
Height (cm)	163	161.5 ± 9.6	163	165.7 ± 8.9	163	169.3 ± 8.2	<0.001	<0.001
Body composition
BMI (kg/m²)	163	20.9 ± 3.3	163	21.4 ± 3.1	163	21.8 ± 3.3	<0.001	<0.001
Waist circumference (cm)	163	68.5 ± 7.1	163	71.1 ± 8.7	163	71.8 ± 8.2	<0.001	<0.001
Waist-to-height ratio (%)	163	42.4 ± 4.0	163	42.9 ± 5.0	163	42.4 ± 4.5	0.016	0.901
Triceps skinfold (mm)	163	13.6 ± 6.2	163	12.7 ± 6.9	163	13.1 ± 7.7	0.003	0.243
Subscapular skinfold (mm)	163	11.2 ± 5.8	163	11.9 ± 6.1	163	11.7 ± 6.6	0.254	0.098
BF (%)	163	19.7 ± 9.4	163	19.5 ± 9.8	163	19.5 ± 11.0	0.474	0.690
Overweight/obesity (%)	163	9	163	15	163	17	0.632	0.869
Physical fitness
Handgrip strength (kg)	163	26.5 ± 7.7	163	30.7 ± 7.8	163	33.9 ± 7.9	<0.001	<0.001
Standing long jump (cm)	163	162.5 ± 32.0	163	171.2 ± 34.8	163	179.1 ± 37.4	<0.001	<0.001
Motor fitness (sec x − 1)^a	163	−12.0 ± 1.1	163	−11.9 ± 1.1	163	−11.6 ± 1.1	0.382	<0.001
Cardiorespiratory fitness (laps)	163	50.8 ± 23.5	163	55.9 ± 24.0	163	59.2 ± 26.6	<0.001	<0.001

Values are mean ± SD or percentages. Overweight and obesity participants were classified according to sex- and age-specific cut-offs proposed by the International Obesity Task Force. Differences between baseline and follow-ups data were performed with paired t-test (p < 0.05). Statistically significant differences are in bold (p < 0.05).

Significant differences between baseline and 1-year follow-up.

Significant differences between baseline and 2-year follow-up.

This score was reverted since lower values in the 4 × 10 test indicate better performance.

BF, body fat; BMI, body mass index; SD, standard deviation.

Table 2 shows indicators of body composition and levels of physical fitness in adolescents with DS and TD by sex group at baseline and in each follow-up visit. In adolescents with DS, males had significantly higher values of waist circumference and performed better handgrip strength, standing long jump, and cardiorespiratory fitness than females at baseline. No significant increases or decreases were seen in the other variables at the 2-year follow-up.

Table 2.

Body Composition and Physical Fitness of Adolescents with Down Syndrome and Typically Developing at Baseline and in Each Follow-Up Visit

	Down syndrome				Typically developing
	n	Males	n	Females	n	Males	n	Females
Baseline
Body composition
BMI (kg/m²)	70	23.4 ± 4.0	41	24.4 ± 4.3	140	21.0 ± 3.5	82	21.2 ± 3.5
Waist circumference (cm)	70	75.0 ± 10.0	41	70.7 ± 7.5	140	70.2 ± 7.7	82	66.7 ± 6.9
Waist-to-height ratio (%)	70	49.8 ± 5.5	41	49.6 ± 5.9	140	42.9 ± 4.1	82	42.0 ± 4.1
BF (%)	68	33.7 ± 14.8	38	35.1 ± 8.2	140	17.2 ± 9.8	82	25.6 ± 7.4
Physical fitness
Handgrip strength (kg)	69	17.5 ± 7.1	40	12.9 ± 4.4	140	29.2 ± 8.2	82	23.2 ± 4.6
Standing long jump (cm)	68	80.9 ± 40.8	41	59.8 ± 27.7	140	175.6 ± 29.9	82	141.8 ± 21.6
Motor fitness (sec x − 1)^a	68	−19.3 ± 5.3	41	−19.9 ± 3.7	140	−11.5 ± 0.9	82	−12.6 ± 0.8
Cardiorespiratory fitness (laps)	68	9.1 ± 6.7	41	6.2 ± 3.2	140	59.9 ± 23.4	82	32.7 ± 12.3
1-year follow-up
Body composition
BMI (kg/m²)	66	24.0 ± 4.2	41	24.8 ± 4.3	119	21.5 ± 3.3	72	21.7 ± 3.5
Waist circumference (cm)	66	76.5 ± 9.1	40	71.4 ± 8.5	119	72.7 ± 8.5	72	68.6 ± 9.1
Waist-to-height ratio (%)	66	50.0 ± 5.5	40	49.8 ± 6.3	119	43.2 ± 4.8	72	43.0 ± 5.4
BF (%)	66	29.4 ± 12.5	40	33.5 ± 7.8	119	17.0 ± 10.3	72	25.0 ± 7.8
Physical fitness
Handgrip strength (kg)	66	18.3 ± 6.4	41	14.8 ± 4.8	118	33.9 ± 7.4	72	25.4 ± 4.2
Standing long jump (cm)	65	79.6 ± 36.5	40	61.3 ± 27.2	117	187.5 ± 30.4	71	144.4 ± 22.8
Motor fitness (sec x − 1)^a	66	−20.6 ± 6.2	40	−20.0 ± 2.9	115	−11.4 ± 0.9	70	−12.7 ± 0.9
Cardiorespiratory fitness (laps)	66	10.2 ± 8.1	39	7.4 ± 3.1	113	67.1 ± 21.0	68	35.5 ± 12.9
2-year follow-up
Body composition
BMI (kg/m²)	66	24.5 ± 4.0	36	25.4 ± 4.5	112	21.8 ± 3.1	58	21.8 ± 3.6
Waist circumference (cm)	65	78.4 ± 9.5	36	73.3 ± 8.6	112	73.6 ± 7.7	58	68.5 ± 8.1
Waist-to-height ratio (%)	65	51.0 ± 5.8	36	51.1 ± 6.3	112	42.7 ± 4.4	58	42.0 ± 4.6
BF (%)	66	29.9 ± 13.4	36	32.1 ± 7.1	112	16.0 ± 10.3	58	26.3 ± 8.6
Physical fitness
Handgrip strength (kg)	66	20.0 ± 7.1	36	14.0 ± 6.9	112	37.9 ± 6.8	58	26.6 ± 3.8
Standing long jump (cm)	64	82.9 ± 33.9	36	66.5 ± 26.6	112	193.7 ± 38.9	58	140.7 ± 30.8
Motor fitness (sec x − 1)^a	66	−19.2 ± 5.5	36	−18.5 ± 2.8	112	−10.8 ± 2.0	58	−12.2 ± 2.5
Cardiorespiratory fitness (laps)	65	11.5 ± 7.8	36	7.3 ± 3.5	108	71.6 ± 22.5	55	34.7 ± 14.1

Values are mean ± SD. Statistically significant differences are in bold (p < 0.05). Differences between males and females were performed with t-test analysis.

This score was reverted since lower values in the 4 × 10 test indicate better performance.

BF, body fat; BMI, body mass index; SD, standard deviation.

For TD adolescents, males had significantly higher waist circumference, lower %BF, and higher scores in all physical fitness variables than females at baseline and at the 2-year follow-up (Table 2). No significant changes were seen in the other variables.

Table 3 shows changes in indicators of body composition and levels of physical fitness of adolescents with DS and TD by sex group. In adolescents with DS, males and females increased in BMI and waist circumference, although males significantly decreased in %BF at the 2-year follow-up. Males increased their levels of handgrip strength and cardiorespiratory fitness, whereas females decreased their levels of handgrip strength and motor fitness at the 2-year follow-up.

Table 3.

Changes in Body Composition and Physical Fitness of Adolescents with Down Syndrome and Typically Developing

	Down syndrome				Typically developing
	n	Males	n	Females	n	Males	n	Females
1-year change
Body composition
BMI (kg/m²)	66	0.6 (0.2, 0.9)	41	0.5 (0.1, 1.0)	119	0.5 (0.1, 0.9)	72	0.5 (0.3, 0.8)
Waist circumference (cm)	66	1.5 (0.3, 2.8)	40	0.7 (−0.1, 1.5)	119	2.7 (2.0, 3.3)	72	2.1 (0.8, 3.4)
Waist-to-height ratio (%)	66	0.4 (−0.4, 1.2)	40	0.2 (−0.5, 0.9)	119	0.3 (−0.1, 0.7)	72	0.7 (0.1, 1.4)
BF (%)	64	−4.1 (−6.8, −1.4)	37	−1.3 (−3.0, 0.5)	119	−0.5 (−1.3, 0.4)	72	−0.2 (−1.0, 0.5)
Physical fitness
Handgrip strength (kg)	65	0.7 (−0.7, 2.0)	40	2.1 (1.0, 3.3)	118	5.1 (4.4, 5.7)	72	2.3 (1.5, 3.1)
Standing long jump (cm)	64	−3.1 (−9.3, 3.1)	40	2.2 (−3.2, 7.5)	117	12.9 (9.9, 16.0)	71	2.5 (−0.7, 5.6)
Motor fitness (sec)^a	65	1.3 (0.7, 2.0)	40	0.1 (−1.0, 1.1)	115	−0.1 (−0.2, 0.1)	70	0.1 (−0.1, 0.2)
Cardiorespiratory fitness (laps)	65	0.9 (−0.3, 2.1)	39	1.1 (0.3, 1.9)	113	7.3 (4.0, 10.7)	68	2.9 (0.7, 5.1)
2-year change
Body composition
BMI (kg/m²)	66	1.2 (0.8, 1.5)	36	1.3 (0.7, 1.9)	112	0.8 (0.3, 1.3)	58	0.8 (0.4, 1.3)
Waist circumference (cm)	65	3.5 (2.3, 4.7)	36	3.1 (1.4, 4.8)	112	3.7 (2.9, 4.5)	58	2.2 (1.3, 3.1)
Waist-to-height ratio (%)	65	1.2 (0.4, 1.9)	36	1.8 (0.7, 3.0)	112	−0.2 (−0.7, 0.3)	58	0.2 (−0.4, 0.7)
BF (%)	65	−3.8 (−7.1, −0.4)	33	−2.1 (−4.3, 0.1)	112	−1.4 (−2.7, 0.2)	58	1.4 (0.2, 2.6)
Physical fitness
Handgrip strength (kg)	65	2.3 (0.9, 3.7)	35	1.4 (0.5, 2.3)	112	9.2 (8.3, 10.1)	58	3.8 (3.0, 4.7)
Standing long jump (cm)	62	−0.9 (−7.2, 5.3)	36	4.4 (−1.5, 10.3)	112	20.7 (14.3, 27.1)	58	−1.0 (−7.3, 5.4)
Motor fitness (sec)	64	−0.1 (−0.7, 0.6)	36	−1.4 (−2.4, −0.3)	112	−0.8 (−1.2, −0.5)	58	−0.5 (−1.13, 0.1)
Cardiorespiratory fitness (laps)	63	2.0 (0.7, 3.2)	36	0.9 (−0.1, 1.9)	108	11.7 (7.6, 15.8)	55	1.1 (−1.8, 3.9)

Values are mean 95% confidence interval. Statistically significant differences are in bold (p < 0.05). Differences between baseline and follow-up data were performed with paired t-test segmented by sex group (p < 0.05).

This score was reverted since lower values in the 4 × 10 test indicate better performance.

BF, body fat; BMI, body mass index; SD, standard deviation.

In TD adolescents, males increased in BMI and waist circumference but decreased in %BF. Females increased significantly in BMI, %BF and decreased in waist circumference variables in the 2-year follow-up. Males increased in all physical fitness variables, whereas females only increased in handgrip strength variable at the 2-year follow-up.

Table 4 shows the tracking of body composition and physical fitness data from baseline to follow-ups. Pearson correlation coefficients for both follow-ups were moderate to moderately high for body composition (r = 0.546–0.954) and physical fitness (r = 0.579–0.914) in adolescents with DS (all p < 0.001). Similar moderate-to-high values were found for body composition (r = 0.706–0.975) and physical fitness (r = 0.370–0.894) in TD adolescents (all p < 0.001).

Table 4.

Tracking of Levels in Body Composition and Physical Fitness of Adolescents with Down Syndrome and Typically Developing in Each Follow-Up Visit

	Down syndrome					Typically developing
	n	Males	n	Females	n	Males	n	Females
1-year follow-up
Body composition
BMI (kg/m²)	66	0.951	41	0.926	119	0.804	72	0.961
Waist circumference (cm)	66	0.862	40	0.954	119	0.903	72	0.809
Waist-to-height ratio (%)	66	0.815	40	0.944	119	0.975	72	0.797
BF (%)	64	0.706	37	0.796	119	0.900	72	0.912
Physical fitness
Handgrip strength (kg)	65	0.674	40	0.704	118	0.894	72	0.734
Standing long jump (cm)	64	0.798	40	0.814	117	0.852	71	0.818
Motor fitness (sec x − 1)^a	65	0.914	40	0.579	115	0.711	70	0.743
Cardiorespiratory fitness (laps)	65	0.794	39	0.716	113	0.658	68	0.740
2-year follow-up
Body composition
BMI (kg/m²)	66	0.927	36	0.916	112	0.706	58	0.902
Waist circumference (cm)	65	0.880	36	0.819	112	0.825	58	0.906
Waist-to-height ratio (%)	65	0.847	36	0.855	112	0.803	58	0.896
BF (%)	65	0.546	33	0.653	112	0.782	58	0.840
Physical fitness
Handgrip strength (kg)	65	0.695	35	0.810	112	0.828	58	0.678
Standing long jump (cm)	62	0.794	36	0.798	112	0.539	58	0.627
Motor fitness (sec x − 1)^a	64	0.874	36	0.605	112	0.370	58	0.466
Cardiorespiratory fitness (laps)	63	0.763	36	0.623	108	0.566	55	0.694

Values are Pearson's correlation coefficients (r). Statistically significant differences are in bold (p < 0.001).

This score was reverted since lower values in the 4 × 10 test indicate better performance.

BF, body fat; BMI, body mass index; SD, standard deviation.

Discussion

This study examines changes of body composition and physical fitness in a sample of adolescents with DS and TD. The main results of this study show that adolescents with DS increase in most indicators of body composition (BMI, waist circumference, and waist-to-height-ratio) in sex groups, with no significant changes in levels of physical fitness at the 2-year follow-up. Instead, TD adolescents barely increased their indicator of body composition in sex groups. Regarding physical fitness, male TD adolescents improve in all physical fitness components, whereas female TD adolescents only improve in handgrip strength. In addition, moderate-to-high tracking was observed in all body composition and physical fitness variables during all phases of the study. Data obtained in this research are of interest in that, according to the literature, TD girls tend to increase their BF levels during puberty. However, our data suggest a slight increase on indicators of body composition (BMI, waist circumference, waist-to-height ratio) in TD girls. The possibility exists that the findings of this study resulted from the study's limited duration (i.e., 2 years), which afforded only a small window of time when considering adolescent development.¹⁹

Results obtained in the cross-sectional analysis of this study coincide with results found in the literature, since it is observed that adolescents with DS show higher levels of overweight/obesity in different indicators of body composition (i.e., BMI, waist circumference, or waist-to-height ratio) and lower levels of physical fitness than TD peers.²⁰ Further, this population has been associated with a higher prevalence of being overweight and obesity compared with their peers with TD or adolescents with intellectual disability but without DS.^7,21 In this study, we found a higher rate of overweight and obesity in adolescents with DS. Specifically, participants with DS present overweight and obesity at the 1-year follow-up (46%) and 2-year follow-up (47%), whereas this phenomenon was different in TD adolescents. Only 15% and 17% of TD adolescents show overweight and obesity at baseline and at the 2-year follow-up, respectively.

To our knowledge, longitudinal studies concerned with changes in body composition and levels of physical fitness during adolescent years have only incorporated TD participants. To date, little information has been reported on adolescents with DS. In TD adolescents, studies have found different trends on body composition for sex. For example, the literature support that BMI, waist circumference, and waist-to-height ratio increase for adolescent's males and females.^6,19 In contrast, %BF decline, especially for males, because of the rapid growth of fat-free mass and lower accumulation of fat mass in this sex group during adolescence.⁶ In this study, similar trends were seen in adolescents with DS. For both males and females with DS, there were increases in three out of four body composition variables (e.g., BMI, waist circumference, and waist-to-height ratio). In TD adolescents, only BMI and waist circumference increased in both groups and %BF only significantly increased in females.

Regarding physical fitness, some longitudinal studies designed for TD adolescents described the global changes in health-related physical fitness components.²² In general, scientific literature report that there are differences in strength, motor fitness, and cardiorespiratory fitness by sex groups. Specifically, males increase in strength, whereas females tend to maintain their levels of strength during adolescence.²³ Likewise, cardiorespiratory fitness tends to slightly decrease with age in males and females, particularly during and after adolescent growth spurt and sexual maturity.^6,23 Although our findings for TD adolescents are in agreement with the literature, such is not the case for adolescents with DS. For adolescents with DS, significant increases in physical fitness components were only seen in handgrip strength (male and female) and cardiorespiratory fitness (males only) at the 2-year follow-up (Table 3). The possibility exists that these limited increases in physical fitness in the adolescents with DS could be due to delayed motor development, economy, and low efficiency of functioning, or some other health characteristics of this population.²⁴

Studies conducted in TD adolescents suggest that the tracking of obesity in this population is from moderate to high and the tracking of physical fitness is somewhat lower from childhood to adulthood.²⁵ Our results in adolescents with DS showed that all body composition and physical fitness variables present high levels of tracking in adolescents with DS by sex groups. More longitudinal studies that examine different indicators of body composition and levels of physical fitness are needed to compare in a broader and concise way all the data obtained in this study. Future studies should continue to create health-promoting programming to increase physical activity in adolescents with DS, since it would also help to improve these values of physical fitness within DS population.

The strengths of this study are the relatively large sample of adolescents with DS and the sample of control group of TD adolescents. In addition, it represented a comprehensive assessment of body composition variables (BMI, waist circumference, waist-to-height ratio, and %BF) and physical fitness (handgrip strength, standing long jump, motor fitness, and cardiorespiratory fitness) by using a standardized battery for adolescents with DS and TD.

Limitations of this study include: Sample of convenience prevents generalization to the overall DS population; DS sample was sex matched but not age matched to TD sample; measurements of puberty were not performed; and a mean difference of 2 years existed between DS and TD groups. A final limitation concerns the use of BMI to estimate overweight/obesity in people with DS. Due to their short stature, the use of BMI could be misleading and overestimate the prevalence of overweight/obesity.²⁶

In conclusion, the results of this study suggest that components of body composition and physical fitness have different trends in adolescents with DS when compared with adolescents with TD. Understanding the trend of these and other health indicators as youth with DS mature from childhood through adolescence and into young adulthood would be of extreme importance for health professionals and decision makers designing interventions targeting the needs of this population.

Footnotes

Acknowledgments

The authors thank all adolescents with DS, parents, and institutional collaborators in this study. This study was supported by the DEP 2010-21662-C04-00 grant from the National Plan for Research, Development and Innovation (R+D+i) MICINN.

UP&DOWN group: Coordinator: Ascension Marcos. Principal Investigators: Ascension Marcos, Oscar L. Veiga, Jose Castro-Piñero, and Fernando Bandrés. Scientific Coordinators: David Martinez-Gomez (chair), Jonatan R. Ruiz (co-chair), Ana Carbonell-Baeza, Sonia Gomez-Martinez, and Catalina Santiago. Spanish National Research Council: Ascension Marcos, Sonia Gomez-Martinez, Esther Nova, Esperanza L. Diaz, Belén Zapatera, Ana M. Veses, Jorge R. Mujico, and Alina Gheorghe. Autonomous University of Madrid: Oscar L. Veiga, H. Ariel Villagra, Juan del-Campo, Carlos Cordente (UPM), Mario Diaz, Carlos M. Tejero, Aitor Acha, Jose M. Moya, Alberto Sanz, David Martinez-Gomez, Veronica Cabanas-Sanchez, Gabriel Rodriguez-Romo (UPM), Rocio Izquierdo-Gómez, Laura Garcia-Cervantes, and Irene Esteban-Cornejo. University of Cadiz: José Castro-Piñero, Jesús Mora-Vicente, José L. González-Montesinos, Julio Conde-Caveda, Francisco B. Ortega (UGR), Jonatan R. Ruiz (UGR), Carmen Padilla Moledo, Ana Carbonell Baeza, Palma Chillón (UGR), Jorge del Rosario Fernández, Ana González Galo, Gonzalo Bellvís Guerra, Álvaro Delgado Alfonso, Fernando Parrilla, Roque Gómez, and Juan Gavala. Complutense University of Madrid: Fernando Bandrés, Alejandro Lucia (UEM), Catalina Santiago (UEM), and Felix Gómez-Gallego (UEM).

Author Disclosure Statement

No competing financial interests exist.

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