Physical activity as a predictor of body composition in American Indian children.

OBJECTIVE: To examine physical activity in second grade American Indian children as a predictor of percentage body fat 3 years later. RESEARCH METHODS AND PROCEDURES: Physical activity was assessed as average vector magnitude (AVM) counts from an accelerometer in 454 second grade children as part of the Pathways study. BMI was assessed, and skinfolds and bioelectrical impedance were used to estimate fat mass, fat-free body mass, and percentage body fat in validated prediction equations. Associations were examined using mixed models regression controlling for baseline body composition.
RESULTS: In normal-weight children, higher AVM counts were significantly associated with decreases in percentage body fat. Among overweight children, higher AVM counts were significantly associated with increases in BMI, fat mass, and fat-free mass but not percentage body fat. DISCUSSION: Higher physical activity levels in second grade were associated with lower levels of percentage body fat in fifth grade in normal-weight but not in overweight children. BMI showed no association with physical activity among normal-weight children, and increases in BMI were associated with increasing amounts of physical activity among overweight children. These findings emphasize the importance of valid body composition measures and may indicate important differences in associations between physical activity and adiposity in normal-weight as compared with overweight children.