Injections of human growth hormone can improve sprint capacity enough to turn the last-place finisher in the Olympic 100-meter dash into a gold-medal winner, according to a study released Monday.
Sprint capacity improved for both men and women, the study said. Combining growth hormone with testosterone injections in men doubled the improvement in sprinting.
"This is helpful in showing those skeptics out there who say it doesn't help performance that they're wrong," said David Howman, director general of the Montreal-based World Anti-Doping Agency, which funded the study.
Howman and other sports medicine experts said the finding should serve as a warning to those U.S. professional sports organizations that have resisted testing for growth hormone — which is banned by athletic organizations — because they say the substance is too difficult to detect.
Although the hormone can't be detected in urine, it can be found in a blood sample if the test is performed within a few days of use, Howman said. Professional sports leagues should consider unannounced, out-of-competition testing, he said.
"They should wake up and see they should be putting a lot more effort into detection of this substance," he said.
The eight-week study, one of the most rigorous examinations of growth hormone and athletic performance to date, involved 96 healthy, recreationally trained athletes with an average age of 27. The 63 male participants were assigned to receive one of four regimens: two milligrams per day of growth hormone; 250 milligrams per week of testosterone; both growth hormone and testosterone; or placebo injections. The 33 female participants received either growth hormone or placebo injections.
The athletes underwent physical examinations, laboratory tests and performance evaluations. Neither the researchers nor athletes knew who was receiving the hormone and who was receiving the placebo.
After eight weeks, researchers found that growth hormone improved sprint capacity in men and women by an average of 3.9% over the placebo group — which would trim 0.4 of a second from a 10-second time in the 100-meter dash, said study lead author Dr. Kenneth Ho at St. Vincent's Hospital in Sydney, Australia. In the 2008 Olympics, the top three male finishers had times of 9.69, 9.89 and 9.91 seconds.
That same 3.9% improvement could cut 1.2 seconds from a 30-second time in a 50-meter swim, Ho said.
Men who received both growth hormone and testosterone had an 8.3% average increase in sprint capacity, the study found.
The report, which was published in the Annals of Internal Medicine, also found that growth hormone reduced body fat and increased lean body mass. Participants taking the substance complained of swelling and joint pain, and performance in sprint measures returned to normal six weeks after the growth hormone injections stopped. Although sprint performances improved, measures of strength or power were unaffected, the authors said.
Dr. Gary Wadler, a professor of medicine at New York University, noted that the test showed that testosterone, which can be detected in urine, could be combined with growth hormone at low enough levels to improve performance but escape detection of either substance.
"It's concerning that athletes could take levels low enough that it would not result in a positive urine testosterone test," said Wadler, who is the chairman of a World Anti-Doping Agency committee on banned substances.
In the real world, athletes are likely to use much higher doses than those used in the study, added Ho, who is an endocrinologist.
"We think the real effects of growth hormone are, or could be, far greater than what's reported in our paper," he said. "Equally, the side effects could be much more serious."
The World Anti-Doping Agency hopes to release a second blood test this year that would identify markers for growth hormone. That test would expand the window of detection from a few days to several weeks after a growth hormone injection, Howman said.
In March, the World Anti-Doping Agency called on Major League Baseball and its players' union to begin testing for human growth hormone. Baseball officials said they were considering the matter.
Human growth hormone is produced naturally in the body, where it plays a key role in muscle and organ growth.