Efficacy of Testosterone plus NASA Exercise Countermeasures during Head-Down Bed Rest

Area of Science:

• Exercise physiology
• Endocrinology
• Space medicine

Background:

• Prolonged head-down bed rest (HDBR) causes musculoskeletal losses comparable to long-duration space flight.
• Current exercise countermeasures alone do not fully prevent muscle mass and function decline.

Purpose of the Study:

• To assess the safety and efficacy of intermittent, low-dose testosterone combined with NASA exercise (SPRINT) countermeasures.
• To evaluate these interventions during a 70-day HDBR period.

Main Methods:

• Healthy men were randomized into inactive (CON), exercise with placebo (PEX), or exercise with testosterone (TEX) groups.
• Testosterone (100 mg/wk) or placebo was administered cyclically during 70 days of 6° HDBR.

Main Results:

• Testosterone treatment (TEX) increased lean body mass (LBM) and decreased fat mass, unlike CON and PEX groups.
• Exercise alone (PEX) largely maintained LBM and strength compared to CON.
• Leg strength changes positively correlated with leg LBM changes.

Conclusions:

• Testosterone supplementation enhances exercise efficacy in preventing body composition changes during HDBR.
• Cycled, low-dose testosterone effectively increases LBM under strict exercise conditions.
• Findings are relevant for combating muscle atrophy in aging, disease, and potentially space flight.