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International Journal of

Environmental Research

and Public Health

Article

Tai Chi as an Alternative Exercise to Improve PhysicalFitness for Children and Adolescents withIntellectual Disability

Zhaowei Kong 1 , Tat-Ming Sze 1, Jane Jie Yu 2, Paul D. Loprinzi 3 , Tao Xiao 4 ,Albert S. Yeung 5, Chunxiao Li 6 , Hua Zhang 1 and Liye Zou 7,*

1 Faculty of Education, University of Macau, Macao, China; zwkong@um.edu.mo (Z.K.);tmsze@um.edu.mo (T.-M.S.); frank2011macau@gmail.com (H.Z.)

2 Department of Sports Science and Physical Education, the Chinese University of Hong Kong, Shatin, HongKong, China; jieyu0203@gmail.com

3 Department of Health, Exercise Science and Recreation Management, The University of Mississippi,University, MS 38677, USA; pdloprin@olemiss.edu

4 College of Mathematics and Statistics, Shenzhen University, Shenzhen 518060, China; taoxiao@szu.edu.cn5 Depression Clinical and Research Program at the Massachusetts General Hospital, Harvard Medical School,

Boston, MA 02115, USA; ayeung@mgh.harvard.edu6 Physical Education and Sports Science Academic Group, National Institute of Education, Nanyang

Technological University, Singapore 637616, Singapore; cxlilee@gmail.com7 Lifestyle (Mind-Body Movement) Research Center, College of Sports Science, Shenzhen University,

Shenzhen 518060, China* Correspondence: liyezou123@gmail.com; Tel.: +86-188-2343-7684

Received: 12 February 2019; Accepted: 28 March 2019; Published: 30 March 2019�����������������

Abstract: Objective: The purpose of this study was to investigate the effects of Tai Chi (TC) onanthropometric parameters and physical fitness among children and adolescents with intellectualdisabilities (ID). Methods: Sixty-six Chinese individuals engaged in sport-related extracurricularactivities (TC and aerobic exercise (AE)) as exercise interventions or arts/crafts activities as acontrol condition (CON). The experimental protocol consisted of a baseline assessment, a 12-weekintervention period, and a post-intervention assessment. Results: Significant interaction effect wasonly observed in the performance of a 6-min walk test. After 12 weeks of intervention, the AE grouphad significant changes in body mass index (p = 0.006, d = 0.11), sit-ups (p = 0.030 and d = 0.57),and 6-min walk test (p = 0.005, d = 0.89). Significant increases in vertical jump (p = 0.048, d = 0.41),lower-limb coordination (p = 0.008, d = 0.53), and upper-limb coordination (p = 0.048, d = 0.36)were observed in the TC group. Furthermore, the TC group demonstrated significantly greaterimprovements on balance compared to the control group (p = 0.011). Conclusions: TC may improveleg power and coordination of both lower and upper limbs, while AE may be beneficial for bodymass index, sit-ups and cardiorespiratory fitness.

Keywords: mind–body movement; aerobic exercise; balance; BMI; coordination; flexibility;developmental disability

1. Introduction

Regular physical activity (PA) is essential for health development of children and adolescents [1].Strong and consistent evidence has demonstrated that regular PA participation is associated with areduced risk of becoming overweight or obesity, and the reduced likelihood of cardiovascular diseases,high blood pressure, and other metabolic dysfunctions [2]. The World Health Organization has

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recommended that all children and adolescents, including those with disabilities, should accumulateat least 60 min spent in moderate-to-vigorous-intensity PA each day [3]. However, children andadolescents with disabilities hardly meet this PA guideline [4] and are at a much higher risk ofobesity when compared to their counterparts without intellectual disabilities (ID) [5]. A recent studyshowed that children and adolescents with ID participate in substantially less PA than other disabilitygroups [6] and, thus, should be a target population for PA and health promotion.

Physical inactivity of individuals with ID may, in part, be influenced by their poor physicalfitness [7]. Children with ID usually have a lower level of physical fitness (e.g., aerobic endurance,strength) and a higher level of adiposity in comparison to the general population, and such situationsmay persist into adulthood without effective interventions or remediation [8,9]. In recent decades,exercise programs have received greater attention in improving physical fitness in individuals withID, and the exercise training is varied in its form with aerobic training being the most popular [10].A meta-analysis by Shin and Park [11] reported that exercise interventions had a positive effect onboth health- and skill-related physical fitness (e.g., cardiovascular fitness, muscular endurance, andmuscular strength) in this population. However, it is worth noting that previous studies targetedadults with ID rather than children or adolescents with ID.

In adolescents with ID, a recent meta-analysis showed that exercise training has a significantpositive effect on several components of skill-related physical fitness, including agility, power, andcoordination, but the existing forms of exercise or therapy are not effective in improving balance [12].Jeng et al. [12] suggested the need to improve lower limb strength due to its close association withbalance in adolescents with ID.

Tai Chi (TC) is widely acknowledged as a feasible activity to improve functional capability andhealth for people with varied health conditions, such as older adults, patients with chronic diseases,and children with ID [13–17]. Features of TC emphasize dynamic shifting of body weight at a slowpace (require strong lower-limb fitness), integrated with breathing control, body awareness, and mentalfocus [18–20]. TC practice has been reported to be effective in improving physical fitness in numerousstudies [21–23], yet few of them were conducted among individuals with ID. Notably, only two studieshave evaluated the effects of TC on physical fitness in individuals with ID [24,25]. Azadeh et al. [24]demonstrated feasibility and effectiveness of TC practice on balance in female adolescents with ID.Kaplan et al. [25] utilized a one-group test–retest experimental design and found that the 24-week TCprogram improved balance, upper extremity reach, and respiration among older adults with moderateto profound ID. However, these two studies are largely limited by their study design (e.g., lack anactive control group) and a small number of physical fitness outcomes assessed.

Therefore, the present controlled trial, with an active control group, aimed to examine whethera school-based TC program is effective in improving both health- (flexibility, body mass index, andbody fat) and skill- (balance, coordination, muscular strength, muscular endurance, and leg power)related physical fitness in children and adolescents with ID. The information gained in this study willaid the development and implementation of feasible exercise programs in enhancing physical fitnessand health in children and adolescents with ID.

2. Methods

2.1. Study Participants

To recruit participants, the principal investigator of this research project made contact with aK-12 school administrator (two local special schools and one integrated school), and informed themabout the purpose of this study, the procedures involved, and the benefits of participating in thisexercise program. To be included in this study, participants had to meet the following inclusioncriteria: (1) aged 10 to 18 years old and be able follow an exercise intervention independently; and(2) be diagnosed with ID, with IQ scores below 70. Individuals were excluded if they: (1) werediagnosed with Down Syndrome; (2) had attended any structured exercise programs in the past 6

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months; and/or (3) were smokers, alcoholics, and/or on medications. The research proposal wasreviewed and approved by the Research Committee of University (Project Identification Number:MYRG 089(Y1-L2)-FED11-KZW). Written informed consent was obtained from legal guardians of theparticipants and school administrators.

2.2. Experimental Design and Study Procedures

The experimental protocol consisted of a baseline assessment, a 12-week intervention, and apost-intervention assessment. Baseline- and post- intervention assessments were completed withinone week prior to the intervention and following the last training session, respectively. Of note, alleligible participants attended two regular school physical education classes (sack race, parachute game,scooter board, tap shoulders, etc.) per week throughout the 12-week intervention period, with eachclass lasting for 40 min. Of the 100 Chinese individuals with ID that were screened, 34 were excludedbecause they did not meet the predetermined inclusion criteria. After the screening, 66 individualsvolunteered to select either sport-related extracurricular activities (TC and aerobic exercise (AE)) asexercise interventions or arts/crafts activities as a control condition (CON). These extracurricularactivities took place at the same time (14:00 to 16:00) as a school day. Furthermore, those individualswho selected sport-related activities were randomly assigned into either TC or AE training. Individualswho chose not to attend extracurricular activities (TC = 4, AE = 3, and CON = 3) and had an attendancerate of ≤60% (TC = 1, AE = 2), were excluded from the data analysis. The study procedures arepresented in Figure 1.

2.3. Intervention Protocol

Participants in both TC and AE groups performed two 60-min sessions per week for 12 weeksin the indoor sports hall, while individuals in the CON group attended to a program involving artsand crafts activities in a usual classroom. All the TC training sessions were administered by a TCmaster with more than 10 years of teaching experience. In each TC training session, the participantsstarted with a 10-min warm-up (jogging and muscular stretching), followed by 40-min TC practiceand a 10-min cool-down. Given that the participants had cognitive impairments, a customized 8-formTC routine (without including beginning and closing movements) was developed by the TC master,including (1) Reverse Reeling Forearm; (2) Brush Knee and Step Forward; (3) Parting the Wild Horse’sMane; (4) Cloud Hands; (5) Golden Rooster Stands on One Leg; (6) Left and Right Heel Kick; (7) WardOff, Rollback, Press and Push; and (8) Cross Hands. Participants in the AE group underwent two60-min aerobic dance sessions per week (i.e., 10-min warm-up activities, 40-min aerobic dance workout,and 10-min cool-down activities). This AE program was administered by a certified physical educatorand personal trainer. Additionally, all participants were asked to maintain their normal daily activitiesincluding two regular physical education classes and restrain from extra exercises throughout the12-week intervention. Exercise intensity during the exercise interventions were recorded by a heartrate (HR) system (Zephyr BioHarness, Auckland, New Zealand) during the entire period at threetime points (week 4, week 8, and week 12), while steps were monitored using a pedometer (YmaxSW-200 digiwalker, Yamax Corporation, Tokyo, Japan) at four time points (week 3, week 6, week 9,and week 12).

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Figure 1. Flowchart shows study procedures including participant selection, outcome assessment, intervention protocol, and data analysis (PE = physical education, TC = Tai Chi, AE = aerobic exercise, CON = control group, PA = physical activity).

2.3. Intervention Protocol

Participants in both TC and AE groups performed two 60-min sessions per week for 12 weeks in the indoor sports hall, while individuals in the CON group attended to a program involving arts and crafts activities in a usual classroom. All the TC training sessions were administered by a TC master with more than 10 years of teaching experience. In each TC training session, the participants started with a 10-min warm-up (jogging and muscular stretching), followed by 40-min TC practice and a 10-min cool-down. Given that the participants had cognitive impairments, a customized 8-form TC routine (without including beginning and closing movements) was developed by the TC master,

Figure 1. Flowchart shows study procedures including participant selection, outcome assessment,intervention protocol, and data analysis (PE = physical education, TC = Tai Chi, AE = aerobic exercise,CON = control group, PA = physical activity).

2.4. Outcome Assessment

2.4.1. Anthropometric Assessment

Anthropometric parameters, including body mass, standing height, skinfold (subscapular, calf,triceps) thickness, and waist and hip girths, were measured. Standing height in bare feet was measuredand recorded as the nearest 0.1 cm. Body mass was assessed using the Bioelectrical Impedance Analyser(Tanita MC-180M, Tanita Corporation, Tokyo, Japan) in light clothing and recorded to the nearest0.1 kg. Body mass index (BMI in kg·m−2) was computed by dividing weight (kg) by squared height(m2). Waist circumference was measured at the level of the smallest circumference above the umbilicusand below the xiphoid appendix. The subcutaneous skinfolds at three sites (triceps, subscapular,and calf) were made on the right side of the body using a Harpenden caliper (British Indicators,Hertfordshire, UK). If the difference between duplicate measures exceeded 1 mm for skinfolds or 1 cmfor the girths, a third measurement was taken. The mean of the two closest duplicate or median oftriplicate anthropometric measurements was used in the analysis. Intra-class correlation coefficientswere between 0.89 to 0.99 for anthropometric measures of girth and skinfold.

2.4.2. Components of Physical Fitness

Components of physical fitness consisted of flexibility, balance, coordination in upper and lowerextremities, muscular strength (grip strength), leg power, muscular endurance, and cardiorespiratory

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fitness. Flexibility was measured using the Sit and Reach Test [26], where participants were instructedto push the sliding metal forward as far as possible; distance between the starting point and the placewhere the sliding metal stopped was recorded, with a longer distance indicating greater flexibility.Balance was measured using the Single-Leg Standing Test [27], where participants were asked to standwith one supporting leg while another leg was bent at roughly 90 degree, with a longer durationindicating greater balance performance. The Hopscotch Test [28] and the Turn-Over-Jars Test [29] wereused to evaluate eye-foot and eye-hand coordination, respectively. Grip strength [30] was measuredwith a digital dynamometer (TKK 5401, Takei Scientific, Niigata, Japan). Lower-limb leg power wasmeasured by the Vertical Jump Test [31], with a jump meter (TKK 5106, Takei Scientific, Niigata,Japan). Three trials for the above tests were performed and the best performance was considered fordata analysis. The One-Minute Sit-up Test and the One-Minute Push-up Test were used to measuremuscular endurance. Intra-class correlation coefficients ranged from 0.84 to 0.98 for these physicalfitness measures. The 6-min walk test (6MWT) is a simple test to assess cardiorespiratory fitness [32].The 6MWT was performed over a 200-m-long sports field, which was marked with a cone at every10 m and a colored tape every 5 m. The number of meters walked was recorded.

2.5. Statistical Analysis

Statistical analyses were performed using the PASW software (Release 22.0; IBM, New York,NY, USA). Chi-square tests and one-way Analysis of Variance (ANOVA) tests were conducted forcategorical data and continuous baseline data, respectively. Given that physical fitness classification isa common way to demonstrate an individual’s fitness level regardless of age and sex, we categorizedthe continuous variables of the observed physical fitness values into ordinal scale outcomes [33], whichincluded five ranks according to local norms [34]. Before the main statistical analyses, the Shapiro–Wilktest was conducted in the outcome variables to verify the normality assumption. The main effects(time or group) and interaction effects (time × group) on the outcome variables were determined usingtwo-way mixed ANOVA with repeated measures. Simple effect tests (Tukey) were performed if therewas a time, group, or interaction effect. Partial eta squared (η2) was used as effect size estimates tomeasure of the main and interaction effects, which were considered as ‘small’ when η2 = 0.01, ‘medium’when η2 = 0.09, and ‘large’ when η2 = 0.25 [34]. Cohen’s d was used to reflect the magnitude of theintervention effect, and d = 0.2 is considered a ’small’ effect, 0.5 represents a ‘medium’ effect and 0.8denotes a ‘large’ effect [35]. Results were presented as mean ± standard deviation (M ± SD), andp < 0.05 was considered as a statistically significant difference.

3. Results

No significant group differences at baseline were found in terms of ID, age, height, and weight,indicating that three groups had similar features (Table 1).

Table 1. Baseline parameters for participants.

Variable TC (15M/2F) AE (14M/3F) CON (16M/3F)

ID levelI (50 to 69) 10 (58.8) 8 (47.1) 11 (57.9)II (35 to 49) 5 (29.4) 6 (35.3) 5 (26.3)III (20 to 34) 1 (5.9) 3 (17.6) 3 (15.8)

IV (<20) 1 (5.9) 0 0Age (years) 15.0 ± 1.8 14.8 ± 2.1 14.8 ± 1.8Height (cm) 160.9 ± 13.3 157.8 ± 11.9 161.3 ± 14.0Weight (kg) 53.6 ± 20.1 53.2 ± 15.1 56.9 ± 18.5

TC, Tai Chi group; AE, aerobic exercise group; CON, control group; M, male; F, female; ID, intellectual disability; I,mild ID; II, moderate ID; III, severe ID; IV, profound ID.

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During the exercise intervention, participants in the TC group (HR mean: 97 ± 9 bpm at week 4and 98 ± 6 bpm at week 8) had lower exercise intensities than the AE group (HR mean: 105 ± 8 bpmat week 4 and 109 ± 8 bpm at week 8) (all p < 0.05). There were no significant group differences insteps at all the four measurement time points, as well as in HR at week 12 (all p > 0.05).

Anthropometric Parameters and Physical Fitness

Results of the primary outcomes are presented in Tables 2 and 3. Anthropometric parameters andphysical fitness characteristics (except for upper-limb coordination) at baseline were not significantlydifferent among the three groups.

Significant interaction effects were only found in 6MWT (p = 0.034, η2 = 0.129). In addition, wefound a significant group effect on balance (p = 0.039, η2 = 0.122), in which the TC group demonstrateda significantly greater improvement on balance as compared to the control group (p = 0.011), and fromits own baseline (p = 0.332, d = 0.21).

There were main time effects, with medium to large effect sizes, in BMI (p = 0.006, η2 = 0.143),sit-ups (p = 0.008, η2 = 0.131), vertical jump (p = 0.019, η2 = 0.106), upper-limb coordination (p < 0.001,η2 = 0.300), lower-limb coordination (p < 0.001, η2 = 0.244), and cardiorespiratory fitness (p < 0.001,η2 = 0.210). Further analyses indicated that the AE group had a significant improvement in BMI (p= 0.006, d = 0.11), sit-ups (p = 0.030 and d = 0.57), and 6MWT (p = 0.005, d = 0.89). In addition, maintime effects, with large effect sizes, were found in upper-limb coordination (p < 0.001, η2 = 0.300)and lower-limb coordination (p < 0.001, η2 = 0.244). Additional analyses demonstrated significantand moderate improvement in vertical jump (p = 0.048, d = 0.41), lower-limb coordination (p = 0.008,d = 0.53), and upper-limb coordination in the TC group (p = 0.048, d = 0.36).

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Table 2. Anthropometric and physical fitness outcomes before and after 12 weeks of intervention.

VariableTC (n = 17) AE (n = 17) CON (n = 19)

Time effect Group effect Interaction effectPre Post Pre Post Pre Post

M ± SD M ± SD M ± SD M ± SD M ± SD M ± SD F p η2 F p η2 F p η2

BMI (kg·m-2) 20.2 ± 5.1 20.4 ± 4.8 21.0 ± 4.2 21.5 ± 4.2 a** 21.5 ± 5.28 21.7 ± 5.0 8.323 0.006 0.143 0.350 0.706 0.014 0.526 0.594 0.021W-girth (mm) 72.6 ± 14.0 71.8 ± 13.2 74.1 ± 3.2 73.6 ± 3.3 75.3 ± 3.0 74.3 ± 3.1 3.510 0.067 0.066 0.178 0.837 0.007 0.168 0.846 0.007H-girth (mm) 85.3 ±12.4 84.3 ± 12.2 86.3 ± 10.1 86.6 ± 10.2 88.6 ± 12.6 88.8 ± 11.6 0.421 0.519 0.008 0.517 0.600 0.020 2.385 0.102 0.087

WHR 0.85 ± 0.05 0.85 ± 0.05 0.84 ± 0.06 0.85 ± 0.06 0.85 ± 0.06 0.83 ± 0.10 0.254 0.616 0.005 0.138 0.872 0.005 1.059 0.354 0.041ΣSKF (mm) 40.7 ± 26.9 38.7 ± 22.7 40.5 ± 17.3 39.9 ± 18.0 45.7 ± 23.6 44.6 ± 23.6 3.099 0.084 0.058 0.336 0.716 0.013 0.348 0.708 0.014

GS 2.9 ± 1.3 3.1 ± 1.3 2.4 ± 1.3 2.5 ± 1.50 2.4 ± 1.0 2.4 ± 1.0 0.134 0.716 0.003 1.386 0.260 0.053 0.202 0.818 0.008Sit-ups 1.1 ± 0.2 1.2 ± 0.4 1.2 ± 0.5 1.6 ± 0.9 a* 1.3 ± 0.7 1.4 ± 1.0 7.547 0.008 0.131 0.847 0.435 0.033 1.667 0.199 0.063

Push-ups 1.2 ± 0.5 1.4 ± 0.7 1.0 ± 0.0 1.0 ± 0.0 1.1 ± 0.5 1.2 ± 0.5 1.709 0.197 0.034 1.984 0.149 0.076 0.779 0.465 0.031Sit & reach 2.5 ± 1.1 2.6 ± 1.0 2.6 ± 0.7 2.7 ± 0.7 2.2 ± 1.2 2.5 ± 1.2 2.462 0.123 0.047 0.205 0.815 0.008 0.296 0.745 0.012

Balance 1.7 ± 1.0 1.9 ± 1.2 1.5 ± 0.8 1.5 ± 0.7 1.3 ± 0.5 1.2 ± 0.4 b** 0.172 0.680 0.003 3.470 0.039 0.122 0.933 0.400 0.036VJ 2.5 ± 1.3 3.0 ± 1.3 a* 2.3 ± 1.3 2.6 ± 1.5 2.2 ± 1.2 2.3 ± 1.3 5.836 0.019 0.106 0.743 0.481 0.029 1.302 0.281 0.050

Up-C (s) 15.3 ± 5.3 13.5 ± 4.9 a** 18.6 ± 5.2 17.3 ± 6.0 15.4 ± 4.9 13.4 ± 3.7 21.000 <0.001 0.300 3.093 0.054 0.112 0.353 0.705 0.014Low-C (s) 16.2 ± 5.3 13.8 ± 3.6 a** 18.6 ± 6.7 16.6 ± 4.6 19.4 ± 7.2 17.7 ± 6.7 a* 15.784 <0.001 0.244 1.942 0.154 0.073 0.131 0.878 0.0056MWT (m) 626 ± 136 671 ± 171 615 ± 151 756 ± 156 a* 673 ± 161 694 ± 103 13.002 <0.001 0.210 0.394 0.677 0.016 3.626 0.034 0.129

TC, Tai Chi group; AE, aerobic exercise group; CON, control group; The physical fitness values were transformed into the ranks of physical fitness according to the norms of Macauresidents based on different ages and genders; Rank 1 stands for “poor”, Rank 2 for “fair”, Rank 3 for “average”, Rank 4 for “good” and Rank 5 for “excellent”. BMI, body mass index;W-girth, waist girth; H-girth, hip girth; WHR, waist hip ratio; ΣSKF; sum of the skinfolds of three sites; GS, grip strength; VJ, vertical jump; Up-C, upper body coordination; Low-C, lowerbody coordination; 6MWT, six-minute walk test. a, compared to pre-test with * (p < 0.05) and ** (p < 0.01); b, compared to the TC group with * (p < 0.05) and ** (p < 0.01).

Table 3. Comparisons in the change ratio (∆%) of outcomes before and after intervention.

VariableTC (n = 17) AE (n = 17) CON (n = 19)

M ± SD d Effect size M ± SD d Effect Size M ± SD d Effect Size

BMI (kg·m−2) 1.5 ± 4.4 0.04 small 2.2 ± 2.8 0.11 small 1.5 ± 4.4 0.04 smallW-girth (mm) −0.9 ± 4.5 0.06 small −0.6 ± 4.3 0.04 small −1.4 ± 3.6 0.07 smallSit-up (reps) 11.8 ± 33.2 0.36 small 38.2 ± 69.7 0.57 medium 6.1 ± 30.0 0.12 smallBalance (s) 29.9 ± 69.5 0.21 small 10.8 ± 60.1 0.12 small −2.6 ± 31.1 0.25 small

VJ (cm) 43.4 ± 75.6 0.41 small 14.6 ± 34.9 0.23 small 3.1 ± 25.0 0.04 smallUp-C (s) −11.2 ± 15.9 0.36 small −7.1 ± 18.4 0.23 small −11.5 ± 12.6 0.47 medium

Low-C (s) −12.3 ± 15.4 0.53 medium −6.9 ± 21.9 0.35 small −8.4 ± 10.8 0.25 small6MWT (m) 7.9 ± 21.3 0.29 small 26.4 ± 29.4 0.89 large 6.0 ± 17.2 0.15 small

TC, Tai Chi group; AE, aerobic exercise group; CON, control group; reps = repetition; s = second; cm = centimeter; The physical fitness values were transformed into the ranks of physicalfitness according to the norms of Macau residents based on the ranks with different ages and genders. BMI, body mass index; W-girth, waist girth; VJ, vertical jump; Up-C, upper bodycoordination; Low-C, lower body coordination; 6MWT, six-minute walk test.

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4. Discussion

The results of our controlled trial showed that both TC and AE programs are effective in improvingphysical fitness among children and adolescents with ID. Given that the 8-form TC is easy to masterand practice, we recommend the simplified TC program for this special population. Our study findingsare further discussed below.

4.1. Tai Chi Versus Aerobic Exercise Program in Exercise Intensity

It is widely accepted that TC, in general, is an aerobic exercise with low to moderate levels ofintensity [36–38]. To determine exercise intensity of the 8-form TC, we measured participants’ HRresponses during practice at week 4, week 8, and week 12. As our participants’ age ranged between 10and 18 years, their maximum HR of 202 to 210 bpm was obtained through subtracting their age rangefrom 220 [39,40]. The HR of participants in the TC group were between 97 and 101 bpm at the threemeasurement points (i.e., 101 to 147 bpm = 50% to 70% of the maximum HR), suggesting the 8-formTC is a program with low to moderate exercise intensity. In general, the TC group showed significantlylower HR response than the AE group. This result suggests that the 8-form TC training may cause lessphysical fatigue in this special population and may subsequently increase their exercise adherence.Step counting has been considered as a popular method of measuring distance [41]. As expected,no significant differences on this outcome was observed between the TC group and the AE group.Therefore, these two programs may induce similar benefits to the participants’ cardiorespiratoryfitness. Heart rates during training at week 4, 8, and 12 are presented as supplementary data (Table S1:Training load during intervention).

4.2. Anthropometric Parameters

Accumulating evidence has shown that children and adolescents with ID are less physicallyactive than their typically developing peers, which could put this special population at greater riskof developing obesity [42,43]. Such physical inactivity may be due to inadequate social and financialsupport and opportunities, problems with transport, the nature of multidimensional impairments, andlack of information on appropriate exercise modalities [44,45]. Thus, more effective exercise trainingoptions that are particularly suitable for this special group should be further explored. In the presentstudy, we explored the effectiveness of the TC program that was specifically designed for children andadolescents with ID. To determine its effects on obesity related parameters, we collected participants’BMI, waist to hip ratio, and skinfolds. It is well-known that in clinical practice and epidemiologicalstudies, BMI is the most commonly used measure to classify overweight and obesity [46]. Interestingly,we observed a significant increase in BMI (d = 0.11) in the CON group. This increase may be dueto normal growth and maturation [47]. In addition, we did not observe any training effect on waistto hip ratio and skinfolds. These insignificant findings on parameters related to obesity may beexplained by a floor effect, as the participants were within a normal weight range. Thus, it awaitsfurther investigations on whether TC training is effective on body composition in overweight andobese individuals with ID.

4.3. Selected Components of Physical Fitness

Children [8,48] and adolescents [49] with ID have demonstrated lower levels of physical fitness incomparison to their counterparts without disabilities. Previous studies had shown that individualswith ID had lower performance on muscular strength, trunk flexibility, muscular endurance, balance,leg power, and motor coordination [50–53]. This poor performance may lead to greater difficultyperforming fundamental movement skills, potentially resulting in lower quality of life [43]. Physicalexercise is widely accepted as a useful strategy to maintain and enhance physical fitness. In the presentstudy, sit-ups in the AE group and four physical fitness outcomes (balance, leg power, upper-limbcoordination, and lower-limb coordination) in the TC group were significantly improved after the

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exercise intervention. These positive findings parallel early review studies [12,54,55] synthesizingexisting evidence regarding the effects of physical exercise training on physical fitness levels amongindividuals without ID. Our results also extended these early studies [25,26], in that TC practice cannot only improve balance but other fitness outcomes among people with ID.

4.4. Strength and Limitations of the Present Study

Strengths of this study include the use of standardized tests, predetermined eligibility criteria,randomized allocation of two experimental groups, qualified TC and AE instructors, and thecustomized 8-form TC. However, this study is not without its limitations. Firstly, this was nota randomized controlled trial because eligible participants with ID were allowed to select eithersport-related programs or arts/crafts courses according to their own interests. Individuals whoselected sport-related programs may have a greater expectation regarding the beneficial effects ofexercise participation. Secondly, one of the investigators was the lead assessor who was not blinded toall experimental procedures, which may bias the assessment results. Thirdly, an improved trend onsome physical fitness outcomes (e.g., grip strength and push-ups) were observed but did not reachstatistical significance, which may be due to the relatively small sample size. The effect sizes obtainedin the present study can be used for sample size calculations in future trials. Finally, because of therestriction of school curriculum, all participants received regular physical education classes whilereceiving exercise interventions. We are therefore unsure if the positive findings in two exercise groupsare attributed to exercise training alone or from integrated effects (TC or AE training plus physicaleducation).

5. Conclusions

The results of the present study indicate that two different training programs have unique benefitson measures of physical fitness. Furthermore, TC may improve leg power and coordination of bothlower and upper limbs, while AE may be beneficial for body mass index, sit-ups, and cardiorespiratoryfitness. In addition, it seems that the 8-form TC is superior to the AE program on improving balance.However, these results should be interpreted cautiously based on the stated limitations of this study.More rigorous studies with a larger sample size should be conducted to further confirm the results ofthis study.

Supplementary Materials: The following are available online at http://www.mdpi.com/1660-4601/16/7/1152/s1, Table S1: Training load during intervention.

Author Contributions: Conceptualization, T.-M.S. and L.Z.; Data curation, Z.K., T.-M.S., J.J.Y., T.X., A.S.Y., C.L.,H.Z. and L.Z.; Formal analysis, J.J.Y. and T.X.; Funding acquisition, Z.K.; Investigation, Z.K. and H.Z.; Methodology,Z.K. and T.-M.S.; Project administration, H.Z.; Resources, Z.K. and L.Z.; Software, T.-M.S.; Supervision, Z.K.;Validation, Z.K. and T.-M.S.; Visualization, Z.K., T.-M.S., J.J.Y., T.X., A.S.Y., C.L., H.Z. and L.Z.; Writing—originaldraft, Z.K., T.-M.S., J.J.Y., T.X., A.S.Y., C.L., H.Z. and L.Z.; Writing—review and editing, Z.K., T.-M.S., J.J.Y., T.X.,A.S.Y., C.L., H.Z., P.D.L. and L.Z.

Funding: The study was supported by a research grant from University of Macau (MYRG089(Y1-L2)-FED11-KZW).The views expressed are those of the authors and not necessarily those of the University.

Conflicts of Interest: The authors declare no conflict of interest.

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