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Growth Hormone Receptor Antagonist Treatment Reduces Exercise Performance in Young Males

Institute of Sports Medicine (K.G., S.D., R.H.N., M.K.), Bispebjerg Hospital, DK-2400 Copenhagen, Denmark; Faculty of Sport Sciences (K.G.), Waseda University, Saitama 359-1192, Japan; and Medical Research Laboratories (A.F.), Aarhus University Hospital, DK-8000 Aarhus, Denmark

Address all correspondence and requests for reprints to: Kazushige Goto, Ph.D., Faculty of Sport Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa, Saitama 359-1192, Japan. E-mail: kgoto{at}aoni.waseda.jp.

Context: The effects of GH on exercise performance remain unclear.

Objective: The aim of the study was to examine the effects of GH receptor (GHR) antagonist treatment on exercise performance.

Design: Subjects were treated with the GHR antagonist pegvisomant or placebo for 16 d. After the treatment period, they exercised to determine exercise performance and hormonal and metabolic responses.

Participants: Twenty healthy males participated in the study.

Intervention: Subjects were treated with the GHR antagonist (n = 10; 10 mg/d) or placebo (n = 10). After the treatment period, they performed a maximal oxygen uptake (O_2max) test and a prolonged exercise test, consisting of 60 min of submaximal cycling followed by exercise to fatigue at 90% of O_2max.

Main Outcome Measures: O_2max was measured before and after the treatment period. Hormonal and metabolic responses and time to exhaustion during prolonged exercise were determined.

Results: Resting serum IGF-I concentration decreased by 20% in the GHR antagonist-treated group (P < 0.05), whereas no change was observed in the placebo group. Conversely, resting serum GH concentration was significantly higher in the treatment group compared with the placebo group (P < 0.01). O_2max did not change significantly in either group after the treatment period. Time to exhaustion at 90% of O_2max was significantly shorter in the treatment group (P < 0.05). No significant differences were observed between the groups in terms of changes in serum free fatty acids, glycerol, O₂, or relative fat oxidation.

Conclusion: GH might be an important determinant of exercise capacity during prolonged exercise, but GHR antagonist did not alter fat metabolism during exercise.