Growth hormone treatment in growth hormone-deficient adults. II. Effects on exercise performance

Abstract

Growth hormone (GH) treatment in adults with GH deficiency increases lean body mass and thigh muscle cross-sectional area. The functional significance of this was examined by incremental cycle ergometry in 24 GH-deficient adults treated in a double-blind placebo-controlled trial with recombinant DNA human GH (rhGH) for 6 mo (0.07 U/kg body wt daily). Compared with placebo, the rhGH group increased mean maximal O2 uptake (VO2max) (+406 +/- 71 vs. +133 +/- 84 ml/min; P = 0.016) and maximal power output (+24.6 +/- 4.3 vs. +9.7 +/- 4.8 W; P = 0.047), without differences in maximal heart rate or ventilation. Forced expiratory volume in 1 s, vital capacity, and corrected CO gas transfer were within normal limits and did not change with treatment. Mean predicted VO2max, based on height and age, increased from 78.9 to 96.0% in the rhGH group (compared with 78.5 and 85.0% for placebo; P = 0.036). The anaerobic ventilatory threshold increased in the rhGH group (+159 +/- 39 vs. +1 +/- 51 ml/min; P = 0.02). The improvement in VO2max was noted when expressed per kilogram body weight but not lean body mass or thigh muscle area. We conclude that rhGH treatment in adults with GH deficiency improves and normalizes maximal exercise performance and improves submaximal exercise performance and that these changes are related to increases in lean body mass and muscle mass. Improved cardiac output may also contribute to the effect of rhGH on exercise performance.

Safety aspects of GH replacement

“…Short-term placebo-controlled studies have demonstrated that GH replacement in adults improves diastolic (29) and systolic (30)(31)(32)(33) functions. The long-term effects of GH replacement on the heart have been investigated in a few open studies.…”

“…The standard incidence ratio (SIR) was calculated with a Swedish cohort of 138 000 of the general population above 18 years of age followed prospectively for 3 years as reference. explain the increased exercise capacity observed in some studies after GH replacement (30,(37)(38)(39)(40) including a recent meta-analysis of placebo-controlled, randomized GH treatment trials (41). However, if a too high dose of GH is given, there is a risk of inappropriate increment in left ventricular mass in elderly GHD adults during longterm treatment.…”

Relationship of chronic endurance exercise to the somatotropic and sex hormone status of older men

“…Adults with complete GH deficiency typically manifest a reduced lean body mass and muscle strength, an increased fat mass and a reduced exercise capacity (5,6). These abnormalities can be at least partially corrected by GH replacement (5)(6)(7)(8).…”

Insulin signaling pathways and cardiac growth

“…Epidemiological data suggest that adults with hypopituitarism have reduced life expectancy and a greater than two-fold increase in cardiovascular disease mortality when compared with healthy controls [24]. Moreover, various GH replacement trials in patients with GH deficiency consistently demonstrated increased LV function (LVEF) with somewhat inconsistent improvements in diastolic function, LV mass and exercise capacity [25][26][27][28].…”