Nearly 8 million American adolescents participate in sports. Many sports (e.g. basketball, volleyball) require powerful muscle movements. Normally, participation declines in young adulthood. The purpose of this study was to assess longitudinal effects of interscholastic high school sport participation and muscle power on young adult bone strength.

295 young adults from the Iowa Bone Development Study participated in this study. Participants were classified into sport participation groups based on an interscholastic sport participation history questionnaire. Groups included Power Sport Participant (PSP), Other Sport Participant (OSP), and Nonparticipant (NP). Current physical activity (PA) behaviors were assessed via questionnaire. Dual x-ray absorptiometry (DXA) assessed hip areal bone mineral density (aBMD) and was used with hip structure analysis (HSA) to estimate femoral neck section modulus (FN Z) and hip cross-sectional area (CSA). Peripheral quantitative computed tomography (pQCT) provided stress-strain index (SSI) and bone strength index (BSI) at 38% and 4% cross-sectional tibial sites respectively. Vertical jump estimated muscle power at age 19. Gender-specific multiple linear regression predicted young adult bone outcomes based on sport participation groups. Mediation analysis analyzed effects of muscle power on relationships between sport participation and bone outcomes. All analyses were adjusted for current PA.

For both males and females, bone outcomes for PSPs were greater than bone outcomes for NPs (P < 0.025). Bone outcomes for PSPs were also greater than OSPs in females (P < 0.025). Mean differences for PSPs and NPs differed between 6.5% to 15.7%. 14.2% to 27.5% of the effect of sport participation on bone outcomes was mediated by muscle power. These results provide evidence to say that former male power sport participants and other sport participants and female power sport participants have stronger bones than peers even when adjusting for current PA. Muscle power did not fully explain differences in all bone outcomes suggesting that sport participation has additional bone health benefits.