Contribution of High School Sport Participation to Young Adult Bone Strength

Introduction Nearly 8 million American adolescents participate in sports. Participation declines in young adulthood. Purpose This study assessed longitudinal effects of high school sport participation and muscle power on young adult bone strength. Methods 228 young adults from the Iowa Bone Development Study completed an interscholastic sport participation questionnaire. Current physical activity (PA) behaviors were assessed via questionnaire. Dual x-ray absorptiometry assessed hip areal bone mineral density and was used with Hip Structure Analysis to estimate femoral neck section modulus and hip cross-sectional area. Peripheral quantitative computed tomography provided strength-strain index and bone strength index at 38% and 4% midshaft tibial sites respectively. Vertical jump estimated muscle power at age 17. 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 strength. Results At follow-up, males participating in any interscholastic sport had greater bone strength than males who did not participate in sport. The explained variability in bone outcomes was 2 to 16%. Females who participated in sports requiring muscle power had greater bone strength than females who did not participate in sports or females who participated in non-power sports (explained variability was 4 to 10%). Muscle power mediated 24.7 to 41% of the effect of sport participation on bone outcomes in males and 19.4 to 30% in females. Conclusion Former male interscholastic sport participants and female interscholastic 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. Address for correspondence: Kathleen F. Janz, Ed.D. F.A.C.S.M., E130 Field House University of Iowa, Iowa City, IA 52242; Email: Kathleen-janz@uiowa.edu This work was supported in part by the National Institute of Dental and Craniofacial Research (R01-DE12101 and R01-DE09551), and by the National Center for Research Resources (UL1 RR024979 and M01-RR00059). The authors report no conflicts of interest. The authors declare that the results of the study are presented honestly, clearly, and without fabrication, or inappropriate data manipulation. The results of the present study do not constitute endorsement by ACSM. Accepted for publication: 10 December 2018. © 2018 American College of Sports Medicine

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