Relationship between BMI, physical fitness, and motor skills in youth with mild intellectual disabilities

Abstract

Introduction: The negative impact of obesity on physical fitness and motor abilities has been documented in youth of various ages; however, this issue has not been explored in youth with mild intellectual disabilities (ID). Youth with ID are considered more overweight, less physically fit, and less motor proficient than peers without ID, so it is important to determine if these variables are associated in this population. The purpose of this study was to examine the relationship between body mass index (BMI), physical fitness, and motor skills in a large sample of youth with mild ID.

Method: A systematic, stratified sampling method was used to select 444 youth with mild ID, aged 6-18 years, from eight special education schools in Hong Kong. Physical fitness was assessed using items from the national Hong Kong assessment: 6- (ages 6-8 years) or 9- (ages 9-18 years) minute run, sit-up, isometric push-up, sit and reach, and sum of skinfold. Functional motor skills were assessed in 244 youth from the fitness sample using the Test of Gross Motor Development-II. Subjects were categorized into normal or overweight/obese BMI groups based on international cutoff points.

Results: Approximately 20% of the sample was classified as overweight/obese (average BMI normal = 17.47+/-2.69; overweight/obese = 24.78+/-4.05). ANCOVA controlling for age and gender revealed group differences in the run (P = 0.001) and push-ups (P = 0.05), but not in the motor or other fitness variables. After controlling for age and gender, BMI was correlated with the run (r = -0.27, P < 0.001) and push ups (r = -0.18, P = 0.008). Age and gender were entered as the first block in hierarchical regression and accounted for most of the variance in all dependent variables, except sit and reach. The inclusion of BMI in the second block added to the model for run and push-ups only (deltaR2 run = 0.04, push-ups = 0.03, P<0.001).

Conclusion: Overweight/obesity is minimally associated with aerobic fitness and muscular strength in youth with mild ID. BMI did not impact other fitness measures (sit-up, sit and reach) or motor skills in the sample. The undesirable level of overweight/obesity in this sample requires increased attention and immediate intervention.