Changes in Tibial Bone Microarchitecture in Response to 8 Weeks of US Army Basic Combat Training in Men and Women: A Preliminary Analysis from a Large Field Study: 3221 Board # June 1 9:55 AM - 10:10 AM

Stress fractures are overuse injuries in bone tissue that are common during Army Basic Combat Training (BCT) when recruits undergo a period of heighted physical activity. The pathophysiology and mechanoadaptive biology that underlie stress fracture development and prevention continue to be characterized. Mechanoadaptation to BCT has been demonstrated in the tibial microarchitecture of female military recruits. Whether male military recruits are able to mount an analogous response to BCT remains to be determined. PURPOSE: To analyze preliminary data from a large prospective field study (427 men and women from a larger cohort of ~4000 recruits to be studied) with the goal of characterizing changes in tibial bone microarchitecture in male and female recruits as a result of 8 weeks of BCT. METHODS: We collected high-resolution peripheral quantitative computed tomography images of the distal tibia (4% from the distal tibial plateau) before and after BCT and analyzed data on 303 male and 124 female recruits who volunteered and completed BCT. Linear mixed models were used to estimate the mean difference for each outcome from pre- to post-BCT, while controlling for race/ethnicity, age, and body mass index. RESULTS: Mean age of male (20.7±3.4 yrs) and female (20.6±3.6 yrs) recruits was similar. At the distal tibia, cortical thickness, trabecular thickness, bone volume/total volume, and total, trabecular, and cortical volumetric bone mineral density (vBMD) increased significantly by 0.50-2.28% (all p<0.0001) over the BCT period in women and by 0.32-1.84% (all p<0.0001) in men. CONCLUSIONS: This preliminary view of data collected to date found that following BCT, both men and women mounted an adaptive response in tibial trabecular bone microarchitecture, indicative of de novo trabecular bone formation. The responses in tibial bone microarchitecture were of greater magnitude in women than in men, which may be due to lower average baseline values in bone microarchitectural properties in women, and therefore potentially greater loading stimuli. Other lifestyle and demographic factors may also influence the adaptive bone response to BCT and will be investigated in the larger sample following study completion.