April 4, 2007 / 6:49 PM / 12 years ago

Activity level correlates with body size in boys

NEW YORK (Reuters Health) - Boys spend nearly twice as much time in vigorous-to-hard physical activity compared with girls, Irish researchers report. And while normal-size boys were more active than overweight or obese boys, no association between activity levels and body size was seen in girls.

The reason for this gender difference is unclear, and should be investigated further, Juliette Hussey of Trinity College Dublin and her colleagues note in the British Journal of Sports Medicine.

Hussey and her team evaluated Irish schoolchildren, between the ages of 7 and 10 years, to better understand relationships among fitness, activity levels and body composition. The children completed a series of fitness tests and wore devices to measure their levels of activity over a four-day period. Body composition and fitness data were available for 224 children, and activity level was obtained for 152 children.

About 20 percent of the children were overweight, while about 6 percent were obese, based on body mass index (BMI). However, more than three quarters had waist circumferences that were larger than the 75th percentile. (BMI is the ratio between weight and height that is commonly used to determine if an individual is underweight or overweight.)

Boys engaged in vigorous-to-hard physical activity for an average of 64.3 minutes daily, compared to 37 minutes for girls. There were no gender differences for sedentary levels. The more time a child of either sex spent being active, the greater was his or her physical fitness level.

However, while higher activity levels correlated with lower BMI and waist size for boys, there was no association between activity levels and BMI or waist size in girls.

Normal-weight boys spent more than 114.3 minutes being at least moderately active compared with more than 96.6 minutes of moderate or more intense activity for normal-weight girls.

Overall, “the evidence for a different relationship between body composition and activity components in girls and boys requires further investigation,” the investigators conclude.

SOURCE: British Journal of Sports Medicine, March 29, 2007.

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