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Exercise Training Benefits Growth Hormone (GH)-Deficient Adults in the Absence or Presence of GH Treatment

Faculty of Physical Education and Health (S.G.T., J.G.E.) and Faculty of Medicine (S.G.T., J.G.E., S.E.), The University of Toronto, Toronto, Ontario M5S 2W6, Canada

Address all correspondence and requests for reprints to: Dr. Scott Thomas, Faculty of Physical Education and Health, University of Toronto, 55 Harbord Street, Toronto, Ontario M5S 2W6 Canada. E-mail:scott.thomas{at}utoronto.ca.

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 µg/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 (VO₂peak) 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. VO₂peak was low at the two baseline measures (B1, 19.3 ± 5.5; B2, 19.9 ± 6.9 ml/kg·min; normal, 30 ml/kg·min) as was VeT (B1, 11.6 ± 2.2 ml/kg·min; B2, 11.7 ± 2.6 ml/kg·min; normal, 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.

This work was supported by a grant from the Heart and Stroke Foundation of Ontario.

The authors have no financial and personal relationships with other people or organizations that could bias this work.

Abbreviations: GHD, GH deficiency; HR, heart rate; POMS, profile of mood states; rhGH, recombinant human GH; VeT, ventilation threshold; V_E/VO₂, ventilatory equivalents for O₂; VO₂peak, peak O₂ uptake.

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