DIETARY CALCIUM ADDS TO THE EXERCISE-ASSOCIATED INCREASE IN FOREARM BUT NOT LEG CORTICAL BONE IN GIRLS

Abstract

It is not yet clear whether additional dietary calcium intake enhances the exercise training-increase in bone mass. Eighty 4th and 5th grade girls enrolled in a seven-month supervised program of jumping (300 jumps per week at ground reaction forces equivalent to 3–5x body weight) and climbing on a mechanical climber (5 min per week) as part of physical education were randomly assigned to receive (Ex+Snack) or not receive (Ex) calcium-rich snacks containing 450 mg calcium daily. A non-randomized group of 54 girls who received normal P.E. and no snack served as a control group (Controls). Forearm and leg muscle and cortical bone volumetric areas were measured on transaxial images acquired using a Norland/Stratec XCT-2000 peripheral computed tomography unit. The 66% site was used on each limb. Forearm and leg tissue responses are shown in the Table. In the forearm, both Ex and Ex+Snack groups significantly increased muscle mass, but Ex had no change cortical bone. The controls' forearm bone and muscle were unchanged. In the leg, there was a trend toward larger increase in EX and Ex+Snack; however, bone and muscle significantly increased by about 10–14% regardless of group. In conclusion, forearm muscle mass increased in growing girls with exercise but cortical bone increased only in the presence of exercise and increased dietary calcium. In contrast, leg bone and muscle increased and dietary calcium did not further enhance leg cortical bone mass gain.Table