Hanse, M., Morthorst, R., Larsson, B., Dall, R., Flyvbjerg, A., Rasmussen, M. H., Orskov, J., Kjaer, M., & Lange, K. H. (2005). No effect of growth hormone administration on substrate oxidation during exercise in young, lean men. Physiology, 567(pt. 3), 1035-1045.

This study examined the effects of supplemental growth hormone on fat availability for oxidative metabolism during exercise. Well-trained males (N = 7) completed four trials: 120 minutes of bicycling at 55% four hours after receiving either a 2.5 mg growth hormone or a placebo injection, and during rest after receiving either growth hormone or a placebo. A standardized meal was given two hours after the injection.

Growth hormone resulted in a ~60-fold increase in serum growth hormone concentration at rest and during exercise. The increase in serum growth hormone was followed by increased circulating glycerol at rest. When combined with exercise, the increase in plasma glycerol was more pronounced. However, the increase in fat mobilization did not increase fat oxidation during exercise.

Implication. Additional growth hormone combined with aerobic exercise increases lipolytic parameters more than exercise alone, but does not alter whole body fat oxidation.

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