Changes In Bone Turnover Biomarkers In Men And Women During Marine Corps Officer Candidates School

Military training environments expose individuals to novel, unaccustomed mechanical loading patterns that can influence bone density, structure, and strength, but structural changes may not be evident for several weeks or months. Bone biomarkers may provide insight regarding the influence of military training on bone adaptation in the shorter term. PURPOSE Examine changes in bone-related biomarkers in men and women undergoing Marine Corps Officer Candidates School (OCS). METHODS Blood samples were collected at the start and end of the 10-week training program to assess markers of bone turnover in 313 men (24.7 ± 0.2 yrs, 80.9 ± 0.5 kg) and 72 women (24.3 ± 0.4 yrs, 65.5 ± 0.8 kg). Enzyme-linked immunoassays were used to determine concentrations of human procollagen type 1 N-terminal propeptide (P1NP), tartrate-resistant acid phosphatase 5b (TRAP5b), osteocalcin (OC), and sclerostin (SOST). Generalized linear mixed-effects models tested the effect of sex (male, female), time (pre, post), and their interaction (sex*time) on each analyte. When significant interaction effects were found, simple main effects with Bonferroni adjustments were used to identify the location of differences; α = 0.05. RESULTS No significant sex*time interactions were observed for P1NP (p = 0.190) or OC (p = 0.983). P1NP (men: 43056.46 ± 1051.54 to 48735.83 ± 1247.97 pg/ mL, women: 33806.12 ± 1551.84 to 42354.64 ± 1598.79 pg/ mL) and OC (men: 24082.75 ± 791.01 to 26315.50 ± 813.52 pg/ mL, women: 18877.65 ± 2483.40 to 21138.77 ± 1637.17 pg/ mL) concentrations increased during training (Main effect time: p < 0.001, p = 0.001) and were greater in men than women (Main effect sex: p < 0.001, p = 0.016). A significant sex*time interaction was observed for TRAP5b (p = 0.008) and SOST (p < 0.001). In men, decreases in concentrations of TRAP5b (3.29 ± 0.04 to 3.22 ± 0.04 U/L, p = 0.019) and SOST (27.49 ± 0.53 to 24.19 ± 0.42 pmol/ L, p < 0.001) were observed, but not in women (TRAP5b: 2.92 ± 0.09 to 3.03 ± 0.09 U/L, p = 0.069; SOST: 22.24 ± 0.90 to 21.61 ± 0.72 pmol/L; p = 0.310). CONCLUSION Following training, biomarkers associated with bone formation increased similarly in men and women, but biomarkers of bone resorption and osteocyte activity only changed in men. Changes in bone metabolism during military training potentially favors positive bone balance, particularly in men. ONR N00014-21-1-2725