A-36 Free Communication/Poster - Bone, Bone Mineral Density, and Connective Tissue Wednesday, May 28, 2014, 7:30 AM - 12:30 PM Room: WB1
Increases in bone formation and resorption have been observed with onset of repetitive mechanical loading. However, changes in bone metabolism following repetitive loading, coupled with severe energy restriction, have not been characterized. Accordingly, U.S. Army Ranger Training School, an 8-wk, physically demanding program (energy expenditure of 2500-4500 kcal/d) with energy restriction (deficit of 1000 kcal/d) provides a unique opportunity to study the combined effects of mechanical loading and energy restriction on bone metabolism.
PURPOSE: To determine the effects of repetitive loading during energy restriction on bone metabolism.
METHODS: Blood was collected from eight men (age: 24±4 yrs; ht: 180±10 cm; body mass: 83±12 kg) before, immediately following, and 2-6 weeks after Army Ranger Training School. Serum was analyzed for bone formation biomarkers [bone alkaline phosphatase (BAP) and osteocalcin (OCN)] and bone resorption biomarkers [C-telopeptide cross-links of type I collagen (CTX) and tartrate-resistant acid phosphatase (TRAP5b)]. Data were analyzed using repeated-measures ANOVA with time as the only factor.
RESULTS: BAP and OCN decreased by 20.8±0.2% (42.5±9.8 to 33.4±8.9ng/ml, p < 0.05) and 29.3±0.1% (16.5±3.5 to 11.5±2.4ng/ml, p ≤ 0.001), respectively, from baseline to immediate post-training, suggesting suppressed bone formation. OCN returned to baseline while BAP remained supressed 2-6 weeks post-training. TRAP5b increased by 80.6±0.3% (3.0±0.3 to 5.4±0.7ng/ml), p < 0.001) from pre- to post-training, suggesting increased bone resorption, and returned to baseline 2-6 weeks post-training. No changes in CTX were detected (p > 0.05).
CONCLUSION: Eight weeks of Army Ranger training increased a bone resorption biomarker. These findings are consistent with the mechanical and metabolic demands of intense physical activity and energy restriction on bone tissue. However, Army Ranger training also resulted in an unexpected suppression of bone formation biomarkers. Overall, these data suggest inhibition of the anabolic response of bone to repetitive loading with severe energy restriction.