Changes In Tibial Bone Microarchitecture Following 8 Weeks Of U.S. Army Basic Combat Training

Abstract

BACKGROUND: Stress fractures affect up to 5% of men and 20% of women undergoing basic combat training (BCT), a physically demanding program that involves repetitive loading of the lower extremities. Animal studies have demonstrated adaptive microarchitectural bone formation following repetitive loading. This adaptive response may reduce the risk of injury. However, no studies have evaluated changes in bone microarchitecture following BCT, due to limitations with in vivo measurement techniques. Recent development of high-resolution peripheral quantitative computed tomography (HRpQCT) allows for assessment of bone microarchitecture in vivo, in humans. PURPOSE: To determine if changes in bone microarchitecture, indicative of adaptive bone formation, occur in female recruits following U.S. Army BCT. METHODS: HRpQCT (XtremeCT II, Scanco Med) images of the distal tibia (4% of tibia length) were collected before and after 8 weeks of BCT. We used linear mixed models for each outcome of interest to estimate the mean difference and its 95% confidence interval (CI) in each microarchitectural bone measurement from pre- to post-BCT. Covariates were decided a priori and included race/ethnicity, age, and body mass index. RESULTS: Data were collected on 91 female recruits (37 African American, 40 Caucasian, 14 Other) with baseline age = 21.5 ± 3.3 yrs and BMI = 23.7 ± 2.8 kg/m2. Mean total volumetric bone mineral density (Tt.vBMD) [1.79%(95% CI: 1.32, 2.25); p<0.001], trabecular vBMD [2.01% (1.44, 2.58); p<0.001], trabecular number [1.21% (0.48, 1.94); p<0.05], trabecular thickness [1.13% (0.76, 1.50); p< .001], and trabecular bone volume/total volume [1.87% (1.31, 2.43); p<0.001] all increased significantly with BCT, whereas trabecular spacing decreased significantly [-1.09% (-1.61, -0.56); p<0.001]. CONCLUSIONS: We observed modest but statistically significant improvements in trabecular bone microarchitecture at the distal tibia after 8 weeks of Army BCT. The changes we observed are consistent with adaptive bone formation. This new bone formation may be an important physiological response to military training and may play a role in prevention of stress fracture. Future studies are needed to determine the relationship between training-related changes in bone microarchitecture and stress fracture risk.