Purpose: To determine the effects of US Army Ranger Training, an 8-week, physically demanding program (energy expenditure of 2,500-4,500 kcal/day) with energy restriction (deficit of 1,000-4,000 kcal/day) and sleep deprivation (<4 h sleep/night) on bone metabolism.
Methods: Blood was collected from 22 men (age 24 ± 4 years) before and after training. Follow-up measurements were made in a subset of 8 subjects between 2 and 6 weeks after training. Serum was analyzed for bone formation biomarkers [bone alkaline phosphatase (BAP) and osteocalcin (OCN)], bone resorption biomarkers [C-telopeptide cross-links of type I collagen (CTX) and tartrate-resistant acid phosphatase (TRAP5b)], calcium, parathyroid hormone (PTH), and vitamin D 25(OH)D increased significantly by 37.3 ± 45.2 % with training [corrected]. A repeated-measures ANOVA with time as the only factor was used to analyze data on the subset of 8 subjects who completed follow-up data collection.
Results: BAP and OCN significantly decreased by 22.8 ± 15.5% (pre 41.9 ± 10.1; post 31.7 ± 7.8 ng/ml) and 21.0 ± 23.3% (pre 15.0 ± 3.5; post 11.3 ± 2.1 ng/ml), respectively, with training, suggesting suppressed bone formation. OCN returned to baseline, while BAP remained suppressed 2-6 weeks post-training. TRAP5b significantly increased by 57.5 ± 51.6% (pre 3.0 ± 0.9; post 4.6 ± 1.4 ng/ml) from pre- to post-training, suggesting increased bone resorption, and returned to baseline 2-6 weeks post-training. PTH Increased significantly by 37.3 ± 45.2% with training. No changes in CTX, calcium, or PTH were detected.
Conclusions: These data indicate that multi-stressor military training results in increased bone resorption and suppressed bone formation, with recovery of bone metabolism 2-6 weeks after completion of training.