Prepubertal exercise increases bone mass, size

Research has shown that children aged 7 to 9 years who exercise daily can increase bone mass and bone size, but a new prospective study reveals the surprising effect of physical activity on prepubertal risk of bone fracture.

Researchers from Sweden have found that a long-term, school-based, moderately intense exercise program increased bone mass at the lumbar spine and bone size at the femoral neck without increasing the number of fractures experienced by a population of prepubescent children.

The researchers followed 446 boys and 362 girls who participated in 40 minutes per day of school physical education for 4 years. A control group consisted of 807 boys and 780 girls who participated in 60 minutes of exercise weekly for the same time frame. All the children participated in a host of activities, including high- and low-impact activities and intensive and endurance training.

At the end of the study period, the researchers used dual-energy radiograph absorptiometry to calculate that lumbar spine bone mineral content was 7.0% higher in the girls and 3.3% higher in the boys in the daily-exercise group than in those in the control group. Similarly, femoral neck width was 1.7% higher in the girls and 0.6% higher in the boys in the daily-exercise group than in the control group.

Surprisingly, the rate ratio for fractures was 1.11 for the cohort, with no sex differences.

In addition to greater bone mass and size, the researchers found that the daily-exercise group also had a greater annual gain in fat mass than the control group. Although the reason is unclear, they surmise that increased activity led to greater appetite and food intake.

The researchers point out that bone size is as important as bone mass; the bigger the bone, the less apt it is to break. They suggest that prepubertal children participate in daily moderate exercise and continue through puberty as a means to optimize bone resistance to fracture.

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