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Am Fam Physician. 2003;68(3):548-550

A recent study demonstrated that physical exercise during childhood and adolescence increases bone mineral content and enhances peak bone mass. These positive changes in bone during the early developmental years may reduce the risk of osteoporosis and osteoporotic fractures later in life. The increased bone mineral content and bone mass appear to be greater in children and adolescents who participate in high-impact sports such as gymnastics; a lesser increase occurs among those involved in low-impact sports such as swimming. All of the studies that evaluated bone mass in young female athletes have used dual-energy x-ray absorptiometry (DEXA) scans. DEXA scans highly correlate with bone strength but cannot assess bone elasticity, internal architecture, or geometry. In addition, DEXA scans are highly influenced by body size. Quantitative ultrasonography has been developed to assess bone properties by using speed-of-sound values. The ultrasound technique is faster, less expensive, and does not involve any radiation exposure compared with the DEXA scan. Falk and associates used qualitative ultrasonography to assess bone properties in prepubertal and early-pubertal female athletes engaged in impact and nonimpact sports.

The participants were healthy girls recruited from local health clubs. To qualify as an athlete, each girl had to participate in year-round training for at least 18 months. Participants included acrobatic gymnasts, swimmers, and a control group. Control patients were girls in the same age group who did not participate in regular physical activity more than two times per week. Participants had to be classified as sexual development pubertal stage (stage 1 or 2) based on their self-reported pubic hair pattern. Medical history information and dietary assessments were performed during the study. In addition, body weight, height, and skinfold thickness were measured. Quantitative ultrasound speed-of-sound measurements were performed at the distal one third of the radius and the midshaft of the tibia. Dominant and nondominant sides were recorded based on which hand the participant used to write.

Study participants included 25 gymnasts, 21 swimmers, and 21 control subjects. The gymnasts were significantly shorter and lighter than swimmers and control subjects, but their body mass indexes were similar to those of the swimmers. The quantitative ultrasound speed-of-sound measurements were not affected by body size. The gymnasts had higher radial speed-of-sound values in their nondominant arm than did the swimmers or the girls in the control group. Tibial values were similar in the gymnasts and swimmers, and were significantly higher than those in the control group. There was no difference within the groups between dominant and nondominant speed-of-sound values.

The authors conclude that high-impact and nonimpact physical exercise improve bone properties in prepubertal and early-pubertal females. The higher values of tibial measurements in the swimmers suggest that sports that require high muscle strain on a bone may improve bone properties in young athletes. These activities may reduce the risk of developing osteoporosis in later life and decrease fracture potential as these persons age.

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