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In a recent survey of the performance-enhancing claims made for dozens of fitness products, researchers found not a single one that could be supported by rigorous scientific research. Moreover, the few fitness products that have been thoroughly evaluated appear to have no effect on strength, endurance, speed or reduced muscle fatigue.

“All the companies say they’ve got a scientific basis for these products,” said the senior author, Dr. Matthew Thompson, a senior clinical scientist at the University of Oxford. “That sounds good until you look at it with an objective scientific point of view.”

Dr. Thompson and his colleagues examined advertising for sports drinks, oral supplements, footwear, clothing and devices like wrist bands and compression stockings in 100 general-interest magazines and the top 10 sports and fitness magazines in Britain and the United States. The researchers excluded bodybuilding magazines and advertisements for weight loss, skin or beauty products, and equipment like bicycles and exercise machines.

The researchers also examined Web sites for any products making claims of enhanced performance or recovery, collecting all references made by manufacturers to studies supporting their claims. Then they assessed the studies, giving the highest quality rating to systematic reviews of randomized trials, second rank to individual randomized trials, third to nonrandomized studies, and the lowest ranking to expert opinion and animal studies.

The researchers examined 615 sports advertisements in magazines. Of these, 54 contained claims that the product enhanced performance, but only three offered references. The 53 Web sites they examined contained 141 references.

They wrote to the companies requesting references to any research they or others had done that was not cited in their advertisements or on their Web sites. Of the 42 companies they contacted, 27 responded and nine provided additional material. Excluding duplicates, books without clinical studies, nonhuman studies, and surveys and articles without data, manufacturers provided 74 studies that could be analyzed for scientific value.

Almost half the participants in the 74 studies were classified as “regular people” who exercise, about 40 percent were endurance athletes and about 11 percent professional athletes. In one study it was unclear who the participants were.

The analysis, published online Thursday in the journal BMJ Open, found only three studies offered by the manufacturers that were judged of high quality and at low risk of bias, but none of these tested a particular product as an intervention. Two were studies of the effect of linoleic acid supplementation, and the other was a controlled trial of magnesium citrate in the treatment of leg cramps. All three had negative results.

One manufacturer of protein drinks and pills, the researchers found, supported advertising claims with a comparative study of the effect of different diets on rat metabolism published in 1930. According to Dr. Thompson, Coca-Cola, which manufactures Powerade, delivered 10 studies. One was paid for with an unrestricted grant from Coca-Cola, and another written by the director of the Gatorade Sports Science Institute.

“The drink companies have created a market,” Dr. Thompson said, “by creating a disease called ‘dehydration’ which needs to be treated or prevented with these expensive drinks — expensive not just in cost but in sugar and calorie intake.”

In an e-mail, a Powerade spokeswoman said: “We always rely on sound, evidence-based science to ensure that our products deliver on their promise to consumers. Powerade was developed in collaboration with sports science experts.”

The American Beverage Association, a trade group, said in an e-mail that the study “exhibits a clear bias by overlooking widely accepted research on sports drinks.” It cited no specific examples of that research.

One expert not involved in the study, Kay Dickersin, a professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health, had some doubts about the authors’ methods. “To know whether these claims are correct,” she said, “you would have to do a systematic review for every topic. As far as they got with the methods, they were O.K., but the claims they make are too strong for the data. There may be evidence out there supporting the claims of the companies.”

Still, Dr. Dickersin continued, “my guess is the claims of these companies are stronger than they should be and that there isn’t a lot data backing them up.”

Dr. Y. Claire Wang, an assistant professor of health policy and management at the Columbia University Mailman School of Public Health, was impressed with the authors’ diligence. “They were very thorough in trying to track down the evidence,” she said, “and I give them a lot credit.”

The authors acknowledge that while they tried to use a representative sample of manufacturers’ claims, it is possible that the products they analyzed were “at the worst end of the spectrum,” and they concede that given more time, some of the companies may have been able to provide more references.

“It’s an interesting study, and it’s not at all surprising to me that the evidence is not really there to support most of the claims,” said Dr. Eric B. Bass, a professor of medicine at Johns Hopkins who was not involved in the study. “As an amateur athlete I realize how powerful that urge is to want to take something that promises to help improve your performance without having to practice harder. But I’m always amazed at how many products are available, and as someone who does evidence-based medicine, I’ve always been somewhat skeptical of the benefits they provide.”