OBJECTIVES: We previously reported significant gains in hip and spine bone mass after 7 months of high-impact training in 89 prepubertal children. Our aim in this investigation was to evaluate the bone response to 7 months of "detraining" in this cohort of children. STUDY DESIGN: Seventy-four boys and girls (n = 37 jumpers, n = 37 controls) from the original cohort completed follow-up testing. Bone mineral content (BMC; g) and bone area (BA; cm2) of the left proximal femoral neck and lumbar spine (L1 to L4) were assessed by dual-energy x-ray absorptiometry. In addition, anthropometric characteristics, Tanner staging, physical activity, and average dietary calcium intake were assessed. RESULTS: Over 14 months, jumpers maintained 4% greater femoral neck BMC and 4% greater femoral neck BA (p < 0.05 and p < 0.01, respectively) than controls. Group differences did not persist at the lumbar spine. CONCLUSION: Gains in both BMC and BA at the femoral neck from high-impact jumping were retained after an equivalent period of detraining. We conclude that this simple exercise may be useful in promoting bone growth at the hip and, thus, enhance peak bone mass.

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