Effects of plyometric jump training on bone mass in adolescent girls

Purpose: The purpose of this study was to investigate the effects of 9 mont hs of plyometric jump training on bone mineral content (BMC), lower extremi ty performance, and static balance in adolescent girls (aged 14.6 +/- 0.5 y r; 22.7 +/- 14.0 months past menarche). Methods: Exercisers (N = 25) traine d 30-45 min, three times per week, performing various exercises using weigh ted vests (squats, lunges, calf raises) and plyometrics (hopping, jumping, bounding, and box depth jumps). The program was designed to load the lower extremities. Controls (N = 28), matched to exercisers for age and months pa st menarche, maintained their usual activities. The following were assessed at baseline and 9 months: BMC, strength by isokinetic dynamometry, power ( Wingate), and static balance. Results: Repeated measures ANOVA revealed no significant differences between groups for BMC, nor were the changes in ant hropometric or performance variables, analyzed by MANOVA, significant. in f ollow-up analyses, t-tests for independent samples revealed that both group s experienced a significant (P < 0.01) increase in percent change in bone m ass compared to zero, for the whole body (mean: 3.7% exercisers, 3.6% contr ols), femoral neck (4.5% vs 2.4%), lumbar spine (L2-4) (6.6% vs 5.3%), and femoral shaft (3.4% vs 2.3%), but only the exercisers improved BMC of the g reater trochanter (3.1% vs 1.9%). Furthermore, the exercise group significa ntly improved knee extensor strength (14.7% vs 7.3%) and medial/lateral bal ance (38.1% vs 9.5%), whereas the control group demonstrated no changes. Th e variety of lateral movement activities performed by the exercise group ma y have contributed to the differences observed between groups for greater t rochanter bone mineral density (BMD), leg strength, and medial/lateral bala nce. Conclusion: The trends observed in bone mass between groups suggest th at plyometric jump training continued over a longer period of time during a dolescent growth may increase peak bone mass.