Testosterone undecanoate administration prevents declines in fat-free mass but not physical performance during simulated multi-stressor military operations.

Male military personnel conducting strenuous operations experience reduced testosterone concentrations, muscle mass, and physical performance. Pharmacological restoration of normal testosterone concentrations may attenuate performance decrements by mitigating muscle mass loss. Previously, administering testosterone enanthate (200 mg/wk) during 28 days of energy deficit prompted supraphysiological testosterone concentrations and lean mass gain without preventing isokinetic/isometric deterioration. Whether administering a practical dose of testosterone protects muscle and performance during strenuous operations is undetermined. The objective of this study was to test the effects of a single dose of testosterone undecanoate on body composition and military-relevant physical performance during a simulated operation. After a 7-day baseline phase (), 32 males (means ± SD; 77.1 ± 12.3 kg, 26.5 ± 4.4 yr) received a single dose of either testosterone undecanoate (750 mg; TEST) or placebo (PLA) before a 20-day simulated military operation (), followed by a 23-day recovery (). Assessments included body composition and physical performance at the end of each phase and circulating endocrine biomarkers throughout the study. Total and free testosterone concentrations in TEST were greater than PLA throughout most of ( < 0.05), but returned to values during . Fat-free mass (FFM) was maintained from to in TEST (means ± SE; 0.41 ± 0.65 kg, = 0.53), but decreased in PLA (-1.85 ± 0.69 kg, = 0.01) and recovered in . Regardless of treatment, total body mass and fat mass decreased from to ( < 0.05), but did not fully recover by . Physical performance decreased during ( < 0.05) and recovered by , regardless of treatment. In conclusion, administering testosterone undecanoate before a simulated military operation protected FFM but did not prevent decrements in physical performance. This study demonstrated that a single intramuscular dose of testosterone undecanoate (750 mg) administered to physically active males before a 20-day simulated, multi-stressor military operation increased circulating total and free testosterone concentrations within normal physiological ranges and spared FFM. However, testosterone administration did not attenuate decrements in physical performance across multiple measures of power, strength, anaerobic or aerobic capacity.