However, regardless of gender, athletes on placebos who thought they had taken HGH typically believed their performance had improved during the study.
What's more, these "incorrect guessers" actually did improve, albeit minimally, in all measures of performance, including endurance, strength, power, and sprint capacity. In one category -- high-jumping ability -- the improvement was significant.
People in the placebo group who correctly guessed that they had taken a placebo improved their performance by about 1 percent to 2 percent, Ho said. But those who mistakenly thought they had taken HGH showed twice that level of overall improvement -- about 2 percent to 4 percent.
"This proof of the placebo effect would equally apply to any drug, at any event, in any sport, and for any athlete, given whatever their coach is giving them," suggested Ho. "And, of course, it also goes beyond sport. It extends to health in general, and medical treatment in general."
How does this placebo effect stack up against improvements linked to actually taking HGH? Ho said his team is working on that comparison, with data coming at a later date.
Meanwhile, Dr. Michael O'Brien, an attending physician in the division of sports medicine at Children's Hospital Boston, called the finding "intriguing."
"This is one of the more unique sports supplement studies I've heard about," he noted. "Professional and elite athletes have always known that there's a very large psychological component to sports, especially with respect to endurance and recovery from hard training. But this is more evidence that more and more chemicals aren't the answer. Particularly for athletes who have a really balanced psychological approach to training."
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