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

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Prolonged confinement to head-down bed rest (HDBR) results in musculoskeletal losses similar to those observed during long duration space flight. Exercise countermeasures by themselves have not completely prevented the deleterious losses in muscle mass or function in HDBR or space flight.


The objective was to investigate the safety and efficacy of intermittent, low-dose testosterone treatment in conjunction with NASA exercise (SPRINT) countermeasures during 70 days of 6° HDBR.


Healthy men (35 ± 8 yrs) were randomized into one of three groups that remained inactive (CON) or performed exercise 6 days per week in addition to receiving either placebo (PEX) or testosterone treatment (TEX, 100mg/week). Testosterone/placebo injections were administered once a week for 2 weeks, followed by two weeks off, etc. during HDBR.


Total, leg, and trunk LBM consistently decreased in CON, increased in TEX, with little or no changes in PEX. Total, leg, and trunk FM consistently increased in CON and PEX and decreased in TEX. Leg strength decreased in CON while PEX and TEX were protected against loss in strength. Changes in leg LBM correlated positively with changes in leg muscle strength.


Addition of a testosterone countermeasure enhanced the preventative actions of exercise against body composition changes during long-term HDBR in healthy eugonadal men. This is the first report to demonstrate that cycled, low dose testosterone treatment increases LBM under conditions of strict exercise control. These results are clinically relevant to the development of safe and effective therapies against muscle atrophy during long-term bed rest, aging, and disease where loss of muscle mass and strength is a risk. The potential space flight applications of such countermeasure combinations deserve further investigations.

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