Testosterone Undecanoate Administration Prevents Fat-Free Mass Loss During Strenuous Multi-Stressor Military Operations

Abstract

PURPOSE: The efficacy of administering testosterone (T) to restore eugonadal concentrations during multi-stressor, sustained military operations (SUSOPS) that suppress endogenous T synthesis to prevent declines in lean mass and physical performance is not well described. Therefore, the objective of this study was to test the effects of T on androgen status, body composition, and physical performance during a simulated SUSOPS. METHODS: After a baseline phase (P1), 32 healthy young males (26.5 ± 4.4 y) received a single injection of either T undecanoate (750 mg; TEST) or placebo (PLA) before completing four consecutive, 5-d simulated SUSOPS cycles (P2). Each cycle consisted of two low-stress days (~1230 kcal/d exercise-induced energy deficit [EDef]; 8 h sleep/night) and three high-stress days (~2800 kcal/d EDef; 4 h sleep/night). P2 was followed by a 23-d recovery period (P3). Circulating hormones, 4-compartment measures of body composition, and physical performance (vertical jump, 3-repetition maximum [RM] deadlift, Wingate anaerobic test, treadmill VO2peak, and 2.5-mile weighted ruck march) were examined at the end of each phase. RESULTS: Total T in TEST was greater by the end of P2 than P1 (mean ± SE between group difference at the end of P2: 6.7 ± 2.6 nmol/L, p < 0.001), which returned to P1 values in P3, but total T did not change in PLA. Despite increases in free T in TEST throughout P2, free T at the end of P2 was not different from P1, but decreased from P1 to P2 in PLA (-1.2 ± 0.6 pmol/L, p = 0.04) and was greater at the end of P3 compared to P1 in PLA (p < 0.05). FFM was maintained across phases in TEST, but decreased from P1 to P2 in PLA (-2.3 ± 1.0 kg, p = 0.02) and recovered in P3. Total body mass and fat mass decreased from P1 to P2 (p < 0.05) and recovered by P3 regardless of treatment. Vertical jump height, 3-RM deadlift, and Wingate peak power decreased, and 2.5-mile ruck march time increased from P1 to P2 (all p < 0.05) and recovered by P3 regardless of treatment. CONCLUSION: Administering T before a 20-d, simulated SUSOPS maintained eugonadal T concentrations and prevented FFM loss without impacting androgen status in recovery. However, T use did not attenuate performance decrements in response to the multi-stressor SUSOPS.