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Physical activity levels affect weight in school age boys, but not girls

American Journal of Clinical Nutrition

The worldwide increase in obesity among children is a significant health problem that may be due in part to decreasing physical activity levels. The years just before puberty (6 to 9 years old) are an important time to target the management and prevention of obesity as an adolescent or an adult. Publishing in this month's American Journal of Clinical Nutrition, Ball et al. studied the calorie intakes and physical activity levels of a group of Australian school children to determine the effect of physical activity on body weight. They found that physical activity in boys had a primary influence on weight measurements, whereas there was no significant relationship between the two variables in girls.

The 106 healthy children in the study averaged 8 years old. Measurements of their height, weight, body mass index (BMI), and percentage body fat were obtained. Total Energy Expenditure (TEE) is a component measurement of total daily calorie consumption, resting metabolic rate, and physical activity level (PAL). Measurement of TEE in this group over a 10-day period resulted in scores that were significantly lower than World Health Organization recommendations for school age children (13% lower for boys and 9% lower for girls). As expected, the percentage of body fat was significantly higher in girls than in boys, while fat-free mass was significantly higher in boys than in girls. In boys, PAL had a significant effect on body weight, BMI, fat mass, and percentage of body fat. There was no significant association in girls between PAL and weight measurements. As a possible explanation of the differences between the sexes, the authors suggest that other factors in girls, such as a greater effect of energy or fat consumption on body fatness, may be a more important determinant of weight than physical activity.

The results imply that, particularly in boys, declines in physical activity may be contributing to the rise in childhood obesity. Appropriate preventive interventions, such as additional emphasis on physical activities during school time, could be targeted to this age group.


Ball, Elizabeth J, et al. Total energy expenditure, body fatness, and physical activity in children aged 6-9 y. Am J Clin Nutr 2001;74:524-8.

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