Short-Term Administration of Supraphysiological Recombinant Human Growth Hormone (GH) Does Not Increase Maximum Endurance Exercise Capacity in Healthy, Active Young Men and Women with Normal GH-Insulin-Like Growth Factor I Axes

Abstract

Context: Despite the fact that the use of GH as a doping agent in sports is widespread, little is known about its short-term effects. Objective: The objective was to study the effects of GH on exercise capacity. Design: A double-blind, placebo-controlled study was used, with a treatment period of 28 d. Setting: Subjects from general community studied ambulatory at a university hospital. Participants: Thirty healthy active young normal volunteers (15 women and 15 men) were recruited by local announcement, and all completed the study. Intervention: All subjects were randomized to receive a low GH dose (0.033 mg/kg·d or 0.1 IU/kg·d), a high GH dose (0.067 mg/kg·d or 0.2 IU/kg·d), or placebo. Main outcome measures: Power output and oxygen uptake on bicycle exercise were the main outcome measures. Results: We found no effect of the low or high dosages of GH on maximum oxygen uptake during exercise (mean ± se for placebo, 45.2 ± 1.6 to 45.2 ± 2.1 ml/kg·min; GH low dose, 42.8 ± 1.6 to 42.8 ± 1.6 ml/kg·min; GH high dose, 44.8 ± 3.4 to 44.8 ± 2.2 ml/kg·min; not significant by two-way ANOVA). Neither was there any effect on maximum achieved power output during exercise or on blood pressure, heart rate, or the electrocardiographic ST level at rest or during exercise. GH significantly increased total body weight (P = 0.028), an effect predominantly ascribed to fluid retention (increased extracellular water volume), whereas muscle mass (as indicated by intracellular water volume) did not change. However, changes in the latter correlated to changes in physical performance, possibly due to different training efforts. Conclusion: Administration of supraphysiological recombinant human GH during a period of 4 wk does not improve power output or oxygen uptake.