Regional Bone Mineral Density of the Tibia in Female Soldiers Following 16-Weeks of Recruit Training

Abstract

The bone adaptation response to exercise is specific to the site being loaded, and may differ between regions of trabecular and cortical bone. It has been suggested that strenuous physical training may result in decreased bone mineral density (BMD) at regions susceptible to stress fracture. Additionally, individuals may respond uniquely to comparable exercise programs. PURPOSE: 1) To determine if regional BMD of the tibia decreases following 16 weeks of recruit training, and 2) to assess whether a change in tibial BMD is related to onset of lower extremity stress fracture. METHODS: 105 women (18.9 ± 0.5 yr) underwent DXA scanning before and after a 16-wk recruit training program in the Israeli Defense Forces. 57 women participated in a physically rigorous combat training program and did not sustain a stress fracture (no stress fracture), 10 participated in rigorous training and were diagnosed with a stress fracture (stress fracture), and 38 completed an academic program with light physical activity requirements (control). BMD was assessed at 5 regions of interest (ROI) at points 4, 33, 50, 66, and 95% from the distal end plate of the tibia. The 4 and 95% regions reflect predominantly trabecular bone; the 33, 50, and 66% sites reflect cortical bone. The 33 and 95% sites are the most frequent site of stress fracture. A total tibial BMD value was calculated as the mean of the five ROIs. Data were analyzed using a repeated measures ANOVA and Tukey post hoc testing. RESULTS: Stress fracture incidence was 14.9% in the combat training group, whereas there were no stress fractures in the control group. The following table presents tibial BMD (g/cm2) compared across groups for each ROI (mean±SD):Table 1Only the control group exhibited changes in tibial BMD over the study period, with increases evident at the 33% and 95% regions. CONCLUSION: Sixteen weeks of strenuous training did not result in decreased tibial BMD, whereas light physical training over the same period increased BMD at two regions, and resulted in a small but significant overall increase in tibial density.