Physical activity patterns in nonobese and obese children assessed using minute-by-minute accelerometry

OBJECTIVE: To determine the levels and patterns of physical activity in a sample of obese (>= 99th percentile body mass index (BMI)) and nonobese ( 99th percentile BMI) children. DESIGN: Cross-sectional study. SETTING: Children were recruited from schools in Bristol and from the childhood obesity clinic, Bristol Royal Hospital for Children. Children were instructed in the use of the accelerometer either while at school or in the clinic, and wore the instrument while carrying out their normal daily activities for 7 days. PARTICIPANTS: A total of 133 children ( mean age 10.5 +/- 0.8 y). In all 11 (16.9%) of the 65 girls and 14 (20.6%) of the 68 boys were classified as obese ( above the 99th percentile for BMI and corresponding to projected adult BMI of 30). MAIN OUTCOME MEASURES: Objectively measured physical activity volume, intensity and pattern. RESULTS: Obese children were significantly less physically active overall than their nonobese counterparts (31 844 +/- 13 200 vs 41844 +/- 10430 counts/h; 95% confidence interval 4407 to 15592; P = 0.001). Similarly the obese children spent less time in physical activity of moderate or greater intensity than the nonobese children ( 9.9 +/- 3.9 vs 12.9 +/- 4.2 min/h; 95% confidence interval 1.15 to 4.80; P = 0.002). Hourly patterns of activity indicated a tendency in obese children to be less active than nonobese children at times when activity was more likely to be determined by free choice, particularly outside of school time. CONCLUSIONS: Obese children demonstrated patterns of physical activity that may have contributed to and are likely to sustain their obesity. Minute-by-minute accelerometry is a valuable tool to investigate physical activity patterns in obese children. It can identify periods when intervention to increase activity may be most appropriate and provide an evidence base for specific exercise prescription in primary and secondary care.