Growth hormone enhances effects of endurance training on oxidative muscle metabolism in elderly women

The present study investigated whether recombinant human (rh) growth hormon e (GH) combined with endurance training would have a larger effect on oxida tive capacity, metabolism, and body fat than endurance training alone. Sixt een healthy, elderly women, aged 75 yr, performed closely monitored enduran ce training on a cycle ergometer over 12 wk. rhGH was given in a randomized , double-blinded, placebo-controlled design in addition to the training pro gram. GH administration resulted in a doubling of serum insulin-like growth factor I levels. With endurance training, peak oxygen uptake increased by similar to 18% in both groups, whereas the marked increase in muscle citrat e synthase activity was 50% larger in the GH group compared with the placeb o group. In addition, only the GH group revealed an increase in muscle L-3- hydroxyacyl-CoA dehydrogenase activity. Body weight remained unchanged in b oth groups, but the GH group showed significant changes in body composition with a decrease in fat mass and an increase in lean body mass. Twenty-four -hour indirect calorimetry performed in four subjects showed a marked incre ase in energy expenditure with increased relative and absolute fat combusti on in the two subjects receiving rhGH. In conclusion, rhGH adds to the effe cts of endurance training on muscle oxidative enzymes and causes a reductio n in body fat in elderly women.