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

Introduction 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. Purpose 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. Method 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. Results 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. Conclusion 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. Correspondence: Edgar L. Dillon, Ph.D. Assistant Professor, The University of Texas Medical Branch, 301 University Blvd. Galveston, Texas 77555, Phone 409-772-8701, eldillon@utmb.edu This study was funded by the National Aeronautics and Space Administration (#NNX10AP86G, RJU/MSM) and conducted with the support of the Institute for Translational Sciences at the University of Texas Medical Branch, supported in part by a Clinical and Translational Science Award (UL1TR000071) from the National Center for Advancing Translational Sciences, National Institutes of Health. Authors have no conflicts of interest. The results of the present study do not constitute endorsement by ACSM. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. Accepted for Publication: 5 February 2018 © 2018 American College of Sports Medicine

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