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For this study, vigorous activity could include actions like running, playing tag, jumping rope, etc. "You don't have to jump rope for half an hour. That would be considered very hard. In reality we are talking about the sort of energy you would expect kids to expend when playing around outside with a ball or rope," said Dr. Eston. "A brisk walk at about 4 mph would do the trick. We are talking about raising the resting energy levels by about 6-8 times. The idea is to 'accumulate' this sort of energy expenditure over the day to total about half an hour," he added.

Abstract

The purpose of this study was to assess the interactive effects of habitual physical activity (total and vigorous intensity) and calcium intake on bone mineral content (BMC) in prepubertal boys and girls.

Seventy-six children, 8 to 11 years old, wore accelerometers for up to 7 days to assess activity. Calcium intake was estimated by a 4-day weighted food diary. BMC and areal density (bone mineral density) were measured at the total body, proximal femur, and femoral neck by using dual-energy X-ray absorptiometry. Moderated regression analyses were used to assess the contributions of physical activity (total and vigorous) and calcium intake to BMC, residualized for bone area and body mass.

Interactive effects of vigorous activity (≥6 metabolic equivalents) and calcium intake were found at the total body in boys (b = 2.90 x 10-3) and in girls (b = 6.58 x 10-3) and at the proximal femur (b = 9.87 x 10-5) and femoral neck (b = 2.29 x 10-5; where b is the regression coefficient from final equation) in boys only.

Residualized BMC was high only if both vigorous activity and calcium intake were high. There were no interactive effects of total (as opposed to vigorous) activity and calcium intake. This study provides evidence for synergistic action of habitual vigorous activity and calcium intake on bone mass in children
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Contact: Stacy Brooks
sbrooks@the-aps.org
301-634-7253
American Physiological Society
28-Sep-2004