Endocrine dynamics of special operations forces across mission cycles: implications for human stress physiology.

Abstract

Purpose: This study investigates the endocrine responses and muscle damage markers in elite male Special Operations Force operators across operational phases to understand hormonal adaptations to extreme operational stress and recovery.

Methods: Fifty-six operators (28-42 years) participated in a longitudinal study conducted at a Special Operations Forces unit. Blood samples were collected at three visits: Visit 1 (baseline recovery), Visit 2 (intensive pre-deployment training), and Visit 3 (post-deployment recovery). Serum concentrations of testosterone (T), cortisol (CORT), dehydroepiandrosterone sulfate (DHEA-S), growth hormone (GH), insulin-like growth factor-I (IGF-I), progesterone (P4), creatine kinase (CK), and myoglobin (Mb) were analyzed.

Results: Post-deployment (Visit 3), T levels increased (+ 20%, p < 0.05), and CORT decreased (- 23%, p < 0.05), resulting in a significantly higher testosterone-to-cortisol ratio compared with Visit 1 and Visit 2 (p ≤ 0.05). DHEA-S correlated with CORT (r = 0.37, p < 0.05), suggesting a compensatory adrenal response under stress. GH concentrations were markedly reduced post-deployment (- 84%, p ≤ 0.05), while IGF-I remained stable, indicating differential regulation within the GH-IGF-I axis during recovery. P4 concentrations remained elevated across all phases, reflecting a consistent endocrine feature across operational phases rather than a defined mechanistic adaptation. No significant changes were observed in CK or Mb, underscoring effective physical stress management at the time of post-deployment sampling.

Conclusion: These findings emphasize the importance of tailored training and recovery strategies for sustaining endocrine balance, resilience, and operational readiness in elite military personnel.