Exercise training benefits growth hormone (GH)-deficient adults in the absence or presence of GH treatment

Reduced aerobic capacity is a prominent manifestation among patients with GH deficiency (GHD). Exercise training may improve the physiological capacity to undertake aerobic activity. The ability of patients with GHD to participate in and benefit from a structured program of aerobic exercise with or without replacement recombinant human GH (rhGH) was investigated. We examined the effect of aerobic training on cycle ergometers in a double-blind crossover trial. Ten patients with GHD trained for 3 months with rhGH (6 microg/kg.d) or placebo, stopped both exercise and drug for 2 months, and resumed training for another 3 months with the other agent. Peak oxygen uptake (VO(2)peak) and ventilation threshold (VeT) were measured during a progressive cycle ergometer test to fatigue or symptom-limited maximum. Serum IGF-I levels were monitored to assess compliance with GH treatment. VO(2)peak was low at the two baseline measures (B1, 19.3 +/- 5.5; B2, 19.9 +/- 6.9 ml/kg.min; normal, approximately 30 ml/kg.min) as was VeT (B1, 11.6 +/- 2.2 ml/kg.min; B2, 11.7 +/- 2.6 ml/kg.min; normal, approximately 16 ml/kg.min). Exercise training increased VeT with (8.6%) or without (9.4%) rhGH treatment. Similarly, exercise training resulted in significant reduction in submaximal heart rate in the presence (-5 +/- 4 beats per minute; P < 0.05) or absence of rhGH treatment (-4 +/- 4 beats per minute; P < 0.05). Peak oxygen uptake was not significantly affected by training with or without rhGH treatment. Our findings suggest that exercise training is a feasible intervention in GH-deficient adults that can measurably improve their submaximal responses to exercise. The beneficial effects of exercise can mimic and are not additive to the effects of GH treatment alone.