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Suppression of endogenous testosterone production attenuates the response to strength training: a randomized, placebo-controlled, and blinded intervention study

¹Institute of Sport Science and Clinical Biomechanics, University of Southern Denmark; and ²Department of Endocrinology, Odense University Hospital, Odense, Denmark

Submitted 24 March 2006 ; accepted in final form 18 July 2006

We hypothesized that suppression of endogenous testosterone would inhibit the adaptations to strength training in otherwise healthy men. Twenty-two young men with minor experience with strength training participated in this randomized, placebo-controlled, double-blinded intervention study. The subjects were randomized to treatment with the GnRH analog goserelin (3.6 mg) or placebo (saline) subcutaneously every 4 wk for 12 wk. The strength training period of 8 wk, starting at week 4, included exercises for all major muscles [3–4 sets per exercise x 6–10 repetitions with corresponding 6- to 10-repetition maximum (RM) loads, 3/wk]. A strength test, blood sampling, and whole body DEXA scan were performed at weeks 4 and 12. Endogenous testosterone decreased significantly (P < 0.01) in the goserelin group from 22.6 ± 5.5 (mean ± SD) nmol/l to 2.0 ± 0.5 (week 4) and 1.1 ± 0.6 nmol/l (week 12), whereas it remained constant in the placebo group. The goserelin group showed no changes in isometric knee extension strength after training, whereas the placebo group increased from 240.2 ± 41.3 to 264.1 ± 35.3 Nm (P < 0.05 within and P = 0.05 between groups). Lean mass of the legs increased 0.37 ± 0.13 and 0.57 ± 0.30 kg in the goserelin and placebo groups, respectively (P < 0.05 within and P = 0.05 between groups). Body fat mass increased 1.4 ± 1.0 kg and decreased 0.6 ± 1.2 kg in the goserelin and placebo groups, respectively (P < 0.05 within and between groups). We conclude that endogenous testosterone is of paramount importance to the adaptation to strength training.

gonadotropin-releasing hormone analog; exercise; isometric strength; lean body mass; fat mass

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