Testosterone Supplementation Enhances Lean Body Mass But Not Lower-Body Muscular Strength and Endurance During Severe Exercise- and Diet-Induced Energy Deficit

Abstract

Sustained periods of severe energy deficit during military operations, produced by significant increases in aerobic-type physical work and limited dietary intake, result in conditions that degrade lean body mass (LBM) and lower-body muscle function, which may be mediated by concomitant reductions in circulating testosterone. Therefore, we studied the effects of restoring testosterone by supplementation (200 mg testosterone enanthate/wk, TEST), compared to placebo (1 mL sesame seed oil/wk, PLA), on body composition and lower-body muscular strength and endurance during 28 d of severe exercise- and diet-induced energy deficit in non-obese, young men. Following energy deficit, concentrations of free testosterone decreased, total testosterone remained unchanged, and sex-hormone binding globulin (SHBG) increased in PLA; whereas, total and free testosterone increased and SHBG was unchanged in TEST, such that, total and free testosterone were greater and SHBG concentrations were lower in TEST than PLA. During energy deficit, TEST attenuated weight loss and increased DXA-derived LBM compared to PLA, but both groups had a similar increase in type I slow twitch myosin heavy chain cross-sectional area (CSA) and decrease in type II fast twitch myosin heavy chain CSA. Lower-body muscle function declines and adverse event rates did not differ by group during energy deficit. Supplemental testosterone may be an effective pharmacological LBM enhancement strategy during short-term periods of exercise- and diet-induced energy deficit in non-obese, young men, but does not appear to mitigate lower-body functional decline. Funding:The research reported in this publication is supported by the Collaborative Research to Optimize Warfighter Nutrition II and III projects and the Joint Program Committee-5, funded by the US Department of Defense. Declaration of Interest: J.C.W., O.T.C., and K.M.G. reported that their institution received funding from the US Department of Defense for work associated with this publication. H.R.L. reported receiving personal fees from Pfizer, Inc., for work outside this publication. All remaining authors declare no competing interests. The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Army or the Department of Defense. Any citations of commercial organizations and trade names in this report do not constitute an official Department of the Army endorsement of approval of the products or services of these organizations. Ethical Approval: This study was approved by the Pennington Biomedical Research Center (PBRC) Institutional Review Board and the Human Research Protection Office of the US Army Medical Research and Materiel Command.