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Growth hormone builds muscle in athletes, but may not help sports performance

The use of human growth hormone (HGH) by athletes as a performance enhancer has grown in recent years, despite the fact it is illegal in the United States. The hormone, approved to treat children and adults who suffer from growth hormone deficiency, increases lean body mass and reduces fat mass. However, serious side effects (diabetes, hepatitis, and acute renal failure) have been observed in athletes taking high-dose growth hormone. Although HGH builds muscle in athletes, it does not seem to enhance sports performance, a new study reveals.

Hau Liu, M.D., M.B.A., M.P.H., and associates at Stanford University reviewed randomized, controlled trials of growth hormone therapy compared with no therapy. They identified 44 papers representing 27 studies that enrolled a total of 440 subjects; 303 of them received growth hormone treatment. Study participants were predominantly male (85 percent), young (mean age of 27 years), lean, and physically fit in terms of respiratory capacity.

Most of the studies reported on changes in body composition, and a majority of the studies looked at the effect of growth hormone on basal metabolism or respiratory exchange. Only two studies looked directly at changes in muscle strength, while another six reported on exercise capacity.

Individuals treated with HGH to improve strength or exercise capacity significantly increased lean body mass by 2.1 kg, but did not appear to improve strength or exercise capacity. Six or twelve weeks of HGH treatment did not increase muscle strength in the biceps or quadriceps. In fact, HGH treatment worsened, rather than improved, exercise capacity in subjects given either a single dose of the hormone or a placebo.

In other studies involving continued administration of the hormone or placebo, metabolic changes observed during rest in hormone-treated subjects failed to carry over into vigorous exercise. Also, HGH-treated subjects reported higher rates of fatigue—consistent with a hormone-associated reduction in exercise capacity.

The researchers caution that the findings are based on a small number of studies. The study was supported in part by a National Research Service Award from the Agency for Healthcare Research and Quality (T32 HS000028).

See "Systematic review: The effects of growth hormone on athletic performance," by Dr. Liu, Dena M. Bravata, M.D., M.S., Ingram Olkin, Ph.D., and others in the May 20, 2008, Annals of Internal Medicine 148(10), pp. 747-758.

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