Who was studied?
103 healthy recreational athletes aged 18 to 40 years who engaged in regular athletic training for at least 1 year.
How was the study done?
The researchers first measured physical fitness and the ability to pull a weight, jump, and sprint on a bicycle. They then assigned half of the group at random to receive either growth hormone or salt water injections for 8 weeks. At the same time, they assigned half of the men at random to also receive testosterone or salt water injections. They measured physical performance at the end of the 8-week period and again at 14 weeks after the athletes had stopped receiving the drug or salt water injections.
What did the researchers find?
Growth hormone increased the athletes’ ability to sprint on a bicycle but had no effects on fitness or their ability to pull a weight or jump. The effect on sprint capacity was nearly doubled in men who also received testosterone injections. Performance returned to normal 6 weeks after participants stopped receiving growth hormone and testosterone injections. Athletes who received growth hormone did not increase muscle mass but retained body fluid and had swelling and joint pain more often than those who received salt water injections.
What were the limitations of the study?
The investigators used lower doses of growth hormone than athletes are reported to use, and for a shorter time. Therefore, the drug’s effects on performance might be greater than in this study, and its side effects may be more serious.
What are the implications of the study?
Growth hormone injections seem to increase athletic sprinting when given alone or in combination with testosterone. The drug also causes a person to retain body fluid. This is the first demonstration of improvement in a particular aspect of physical performance with growth hormone. This effect may bring a competitive advantage for athletes who engage in sprint events.
Participants: 96 recreationally trained athletes (63 men and 33 women) with a mean age of 27.9 years (SD, 5.7).
Intervention: Men were randomly assigned to receive placebo, growth hormone (2 mg/d subcutaneously), testosterone (250 mg/wk intramuscularly), or combined treatments. Women were randomly assigned to receive either placebo or growth hormone (2 mg/d).