Abstract

Objective: The purpose of this study was to investigate the relationships between the time in specific intensities of activity and inactivity, cardio-respiratory fitness and body composition in children.

Methods: A cross-sectional study was conducted in a random sample of schools. Height, weight and waist circumference were measured in 224 children aged 7-10 years. Cardio-respiratory fitness was estimated by the 20-metre multistage running test and physical activity was measured over 4 days by the RT3 (a tri-axial accelerometer). The time spent in moderate and vigorous intensities f activity was calculated.

Results: Twelve schools agreed to participate in the study.Body composition and fitness data was obtained on 224 children. Activity data was obtained on 152 children. Boys were found to engage in approximately twice as much vigorous and hard activity compared to girls (mean and 95% confidence intervals 64.3, 53.2 to 75.4 minutes in boys compared to 37, 33.1 to 40.9 minutes in girls, p<0.001). In boys there was significant difference between those defined as normal, overweight and obese in the time spent in vigorous activity (p<0.05) but no such difference was found in girls. A significant negative correlation between waist circumference and time spent in vigorous activity (r=-0.31, p<0.05) was found in boys but not in girls. Time spent sedentary was positively correlated with waist circumference in boys (r=0.33, p<0.01) but not in girls. In both genders there were significant negative correlations between fitness and both BMI (r=-0.274, p<0.001) and waist circumference (boys: r=-0.503, p<0.01; girls: r=-0.286, p<0.01).

Conclusion: In boys body composition was inversely related to fitness and to vigorous activity and was positively related to inactivity. In girls body composition was related to fitness but not to specific components of physical activity.