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Backing up those fitness claims.Getty Images/Getty Images

Pretty much every fitness product claims to be "backed by science." But a recent spate of lawsuits against the makers of Power Balance bracelets highlights how empty these claims can be. Even for companies trying to do the right thing, navigating the complexities of scientific evidence can be a challenge, as the following examples illustrate.

Power Balance bracelets

The claim: Power Balance makes a range of plastic bracelets and pendants decorated with holographic stickers, which they say will "optimize the body's natural energy flow" to enhance strength, balance and flexibility. The bracelets have been widely adopted by celebrities and professional athletes, including Toronto Blue Jays pitcher Ricky Romero.

The science: There is no science. After being hit with a complaint by the advertising standards board in Australia, the company was forced to issue a statement in December saying: "We admit there is no credible scientific evidence that supports our claims and therefore we engaged in misleading conduct." In March, the company settled a U.S. class action suit out of court, offering refunds to customers. The company's lawyer offered the following explanation: "As with many early technologies, especially one involving Eastern origins" - a familiar excuse - "we recognize the potential for confusion in the marketplace, and concede we got ahead of ourselves with claims about our first product." Meanwhile, the bracelets remain popular, showing that science is no match for celebrity endorsement.

Athletic Propulsion Labs' basketball shoes The claim: APL created a media storm last fall when it hoodwinked the National Basketball Association into banning its shoes. The ban was based on the claim that the shoes enhance vertical jump by "up to 3.5 inches," but the NBA didn't check this claim. Nonetheless, the surge of orders following the announcement shut down the company's website, and sales of the $195 shoes have been booming ever since.

The science: Unlike Power Balance, APL actually performed a study - at an undisclosed "leading United States university." Better yet, it released some of the data - but the graph of 12 participants shows that only one person came anywhere close to improving by 3.5 inches. The average increase looks to be a fraction of an inch at best. The greater concern, though, is how the study was conducted. Was one type of shoe always tested before the other, or was order randomized? How many attempts did subjects get with each shoe? Were subjects told which shoe was supposed to boost their vertical? These are the subtle biases that peer reviewers flag in studies submitted to academic journals - and it's why non-peer-reviewed studies should be taken with a grain of salt.

Reebok's ZigTech apparel with Celliant fibres

The claim: ZigTech sportswear boosts oxygen levels by 7 per cent, thanks to mineral dust incorporated in the fibres. The dust particles reflect infrared energy from the body, increasing blood flow. The material was "initially developed in the 1990s by studying methods to improve natural healing in Asia," according to Celliant, the company that developed the fibre.

The science: On the surface, ZigTech sounds a lot like Power Balance: fancy words, wild claims and some vague hand-waving about Eastern mysticism. But there's a crucial difference: Celliant has funded four external clinical trials, with a fifth under way, one of which was published in the peer-reviewed journal BMC Complementary and Alternative Medicine in 2009. The studies aren't perfect - for example, the one that provides the "7 per cent more oxygen" claim had all the subjects wear a placebo shirt first, followed by the Celliant shirt, instead of randomizing the order. Still, the studies generally suggest that something about the garments really does affect blood flow and oxygen levels. Whether it's enough to make any practical difference to athletic performance hasn't yet been tested.

Sports drinks

The claim: A spate of highly publicized deaths has shown that drinking too much during a marathon can dilute sodium levels until they're dangerously low. Sports drink companies such as Gatorade have argued that their products - which contain sodium - can help avert the danger by keeping sodium levels higher.

The science: In addition to its own in-house research, Gatorade is famous for funding independent research by leading sports scientists around the world. For this, it deserves credit - but it also creates potential conflicts of interest. One of the studies Gatorade funded was a 2008 Penn State paper in the Journal of Applied Physiology that concluded that sports drinks with sodium do indeed help maintain sodium levels. South African scientist Tim Noakes challenged the interpretation of those results, but was unable to get his comments published in the same journal. In a forthcoming issue of the British Journal of Sports Medicine, Dr. Noakes points out that four of the six authors of the most recent American College of Sports Medicine position on hydration are funded by Gatorade, and criticizes what he sees as commercial influence on the publication of research findings.

Beet juice

The claim: Drinking two cups of beet juice offers an instant endurance boost that enables you to run or bike farther and faster. The nitrates in the beet juice are said to reduce the amount of oxygen needed to fuel muscle contractions.

The science: When the first beet-juice-boosts-endurance study emerged in August, 2009, I was skeptical. "Don't look for Tour de France riders or Olympic runners to be downing beet juice any time soon," I wrote on my blog. But the studies kept coming: carefully designed, double-blinded trials comparing beet juice with almost identical nitrate-free beet juice, from researchers in at least three different countries. The most recent study, a few weeks ago, showed a 2.7-per-cent improvement for cyclists racing 16 kilometres after drinking 500 millilitres of beet juice 2.5 hours before the race. Marathon world record-holder Paula Radcliffe has acknowledged experimenting with beet juice, and I have no doubt that some Tour de France riders will be using it this summer.

The lesson: Dismissing claims just because they sound far-fetched can be as misguided as accepting claims without sufficient evidence. Ultimately, the data decides.

Alex Hutchinson blogs about research on exercise at . His new book, Which Comes First, Cardio or Weights?, will be published this month.

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