Relationship between body mass index (BMI) and balance capacity in youth (8-21 yrs) with intellectual disability

Abstract

Adequate skill levels of balance affect activities of daily living, participation in recreational activities, and general physical activity levels of children and adolescents. Most studies of typically developing children and adolescents have reported significant negative relationships between balance (BAL) and body mass index (BMI). That is, the greater the BMI (e.g. overweight, obesity), the lower the scores on tests measuring BAL. The latter relationship is especially of concerns for youth with intellectual disabilities (ID) in that in a systemic literature search estimated that 61% of children and 66% of adolescents were classified as overweight/obese, respectively. To date, only two studies have investigated the relationship between BAL and BMI in children and adolescents with ID and both reported that no negative relationships exist. However, both studies were performed in countries (Hong Kong, Sweden) where participants had significantly lower BMI (i.e., only 20% classified as overweight/obese) than youth with ID reported in the literature. Therefore, the purpose of this study was to determine if a negative relationship exists between BAL and BMI in youths (8-21 yrs) with mild and moderate ID. Participants consisted of 502 youths; 252 from Brazil (159 males [BMI = 21.7±5.8] and 93 females [BMI=21.7±6.7]); and 250 from the United States (160 males [BMI=24.2±7.6] and 90 females [25.0±6.7]). Given that no significant differences existed between balance scores from the Brazil and US participants, we were able to combine the results of the two countries and expand the power of the analysis. Body mass index (BMI, kg/m2 ) was determined by height and weight measurements on the day of testing. Mean BMI and mean age place females in the overweight category and males near the overweight category. Seven (7) balance tests were used from the Bruininks-Oseretsky Test of Motor Proficiency (BOT-2): standing feet apart on a line, eyes open/closed; walking forward on a 4 inch line, normal walking and heel-to-toe walking; standing on one leg on a line, eyes open/closed; and standing on one leg on a balance beam. Because the BOT-2 test scores were not normally distributed due to the BOT-2 celling effect (i.e., stopping at 10 secs and 6 steps), a Kendall's Tau correlation coefficient was used to determine if significant relationships existed. Significance was set at p > 0.5. Although very weak, positive relationships were seen for standing feet apart on a line, eyes open (r = 0.075, p = 0.007) and negative relationships were seen for standing on one leg on a line eyes open (r = -0.066, p = 0.013) and eyes closed (r = -0.055; p = 0.042) and standing on one leg on a balance beam (r = -0.098, p = 0.00004). The results of the present study both compliment and contradict previous studies between BMI and BAL in that r values demonstrate negligible correlation, yet four of the r values are statistically significant. However, with large data sets, as we have in this study, very small correlation coefficients can be "statistically significant." These results suggest that clinicians who use the BOT-2 balance tests to evaluate the balance capacity of youths with ID should be aware that, although some BAL tests demonstrate significant relationships to BMI, the strength of relationships are so negligible that they are not clinically relevant.