As far as performance enhancing drugs are concerned - its all in the athlete's mind.
So concludes a study in which half of recreational athletes received human growth hormone supplements while the other half took a placebo.
This so-called placebo effect was greater in male recreational athletes than in females, said lead author Jennifer Hansen, RN, a nurse researcher at the Garvan Institute of Medical Research in Sydney, Australia.
In a study of growth hormone, the authors tested whether the power of the mind affects physical performance.
"Athletes are doping with growth hormone to improve sporting performance despite any evidence it actually improves performance," Hansen said.
"Therefore, we wanted to know if any improvement in performance is due just to the athletes' belief that they are taking an agent that enhances performance, rather than to the agent itself," she added.
Sixty-four young adult recreational athletes randomly received either growth hormone-a substance banned in sports-or an inactive substance (placebo) for 8 weeks.
Neither the athletes who volunteered for the study nor the investigators knew which substance the athletes received.
At the end of the study, the researchers asked the athletes to guess which agent they had taken and to say if they thought their sporting performance had changed. Then they tested the athletes on physical performance tests of endurance, strength, power, and sprint capacity.
Men were much more likely than women to think they had received growth hormone. Regardless of sex, athletes who took the dummy drug but believed they were on growth hormone ("incorrect guessers") thought their performance improved and actually had some improvement in all measures of performance.
However, jump height (power) was the only test that showed a significantly greater improvement among the incorrect guessers, according to Hansen.
"The results of this study suggest that the placebo effect may be responsible, at least in part, for the perceived athletic benefit of doping with growth hormone for some people," Hansen said.
The research will be presented at The Endocrine Society's 90th Annual Meeting in San Francisco.