Objectively-measured physical activity and body weight in Japanese pre-schoolers

Background: The prevalence of thinness has increased among Japanese children. Aim: The purpose of this study was to examine the association between physical activity and body mass index (BMI) among Japanese pre-school children. Subjects and methods: Subjects were 425 4-6-year-old Japanese girls and boys. Their weights were classified as normal, overweight or thin, based on Cole's international cut-offs for BMI. Physical activity was assessed using a triaxial accelerometer (ActivTracer, GMS) for 6 consecutive days. Results: Physical activity in overweight children was comparable to that in normal-weight children after controlling for age and gender. However, thin children spent significantly greater time engaged in low-intensity activities (physical activity ratio < 2) and spent less time engaged in light-intensity physical activity (2 <= physical activity ratio < 3) and moderate-to-vigorous physical activity (physical activity ratio >= 3) than normal-weight and overweight children, and less time engaged in higher-intensity physical activity (physical activity ratio >= 4) than normal-weight children. Moreover, thin children spent significantly less time engaged in locomotive physical activity than normal-weight or overweight children. Conclusion: This study suggests that thinness, rather than excess weight, is associated with decreased light, moderate and high intensity physical activity in Japanese pre-school children.