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The Effects of Time following Acute Growth Hormone Administration on Metabolic and Power Output Measures during Acute Exercise

Center for the Study of Complementary and Alternative Therapies (B.A.I.), Departments of Human Services (B.A.I., A.W.), Health Evaluation Sciences (J.T.P.), Internal Medicine (S.M.A., W.S.E., A.W.), Obstetrics and Gynecology (W.S.E.), and General Clinical Research Center (B.A.I., J.T.P., D.D.W.-W., K.I.F., A.W.), University of Virginia, Charlottesville, Virginia 22908; and Endocrine Research Unit (J.D.V.) and General Clinical Research Center (J.D.V.), Mayo Clinic and Foundation, Rochester, Minnesota 55905

Address all correspondence and requests for reprints to: Arthur Weltman, Ph.D., Exercise Physiology Laboratory/Memorial Gymnasium, University of Virginia, Charlottesville, Virginia 22904. E-mail: alw2v{at}virginia.edu.

We examined the effects of GH infusion on metabolism and performance measures during acute exercise. Nine males [(X ± SEM): age 23.7 ± 1.9 yr, height 182.6 ± 1.6 cm, weight 77.3 ± 2.6 kg, percent fat 17.7 ± 1.9%, peak oxygen consumption 37.9 ± 2.9 ml/kg·min] completed six 30-min randomly assigned bicycle ergometer exercise trials at a power output midway between the lactate threshold and peak oxygen consumption. In five of the six trials, the subjects received a recombinant human GH infusion (10 µg/kg, 6-min square wave pulse) at 0800 h, followed by a 30-min exercise trial initiated at one of the following times: 0845, 0930, 1015, 1100, or 1145 h. During one of the six trials, the subject received a saline infusion followed by a 30-min exercise trial initiated at 0845 h. Mixed-effect, repeated-measures ANOVA analyses corrected for multiple comparisons revealed that there were no significant condition effects for total work, caloric expenditure, heart rate response, the blood lactate response, or ratings of perceived exertion response. However, acute GH administration resulted in a lower exercise oxygen consumption without a drop-off in power output. We conclude that the time of exercise initiation after GH infusion does not affect total work, caloric expenditure, heart rate response, blood lactate response, or ratings of perceived exertion but reduces oxygen consumption in response to 30 min of constant load exercise at an intensity above the lactate threshold. The last outcome may suggest that GH administration can improve exercise economy.

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