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Purpose.To determine the effect of two jumping programs on hip bone mineral density (BMD) in women.Design.Randomized controlled trial.Setting.Approximately 20 cities in the Mountain West.Subjects.Sixty premenopausal women, aged 25 to 50 years, completed the intervention.Intervention.Subjects were randomly assigned to a control group or one of two jumping groups. The Jump 10 group performed 10 jumps with 30 seconds rest between jumps, twice daily for 16 weeks, while the Jump 20 group performed the same protocol but with 20 jumps.Measures.Hip BMD was measured by using dual-energy x-ray absorptiometry.Analysis.Analysis of variance and covariance.Results.At 8 weeks, unadjusted percentage change in hip BMD was significantly different among groups (F = 5.4, p = .0236). Specifically, compared with controls, the Jump 20 women had significantly greater gains in hip BMD and the Jump 10 women had marginally greater improvements. Following 16 weeks of jumping, differences between the Jump 10 and the Jump 20 groups compared with controls were significant (F = 4.2, p = .0444), especially after adjusting for the covariates (F = 7.3, p = .0092).Conclusion.After 16 weeks of high-impact jump training, hip BMD can be improved in premenopausal women by jumping 10 or 20 times, twice daily, with 30 seconds of rest between each jump, compared with controls.