Shaquille O'Neal swears by them. The Power Balance bracelet, he says, gives him a competitive edge on the court. It's no gimmick, he says. It's for real.

It may be for him, but Australian authorities say the California-based company behind the wildly popular wristbands and pendants has no business claiming that they improve balance, strength and flexibility.

And they even got Power Balance to admit it.

The company wrote: "We admit that there is no credible scientific evidence that supports our claims." It also agreed to give refunds to customers who believe they were cheated.

The company's admission, however, hopped across the globe since its agreement with the Australian Competition and Consumer Commission was announced on Dec. 22.

It was an answer to what many who saw the ads wondered: Do the colorful silicone bands actually work?

Critics railed against the company on Twitter and those who had believed in the bracelet's power.

The company unleashed a torrent of its own tweets, playing off the word "admit."

In one, it said: "Power Balance Admits products have been worn during the last world series, nba finals and super bowl champions!"

Fans insist the bands have helped their game.

"Our trainers swear by it," Phoenix Suns forward Jared Dudley wrote in a message posted on his Twitter page.

The company began selling bracelets in 2007 embedded with holograms that were purportedly designed to interact with the body's natural energy flow.

Since then, the colorful wristbands, which sell for $29.95, have become ubiquitous, donned by Los Angeles Lakers' Lamar Odom and English celebrity soccer star David Beckham.

They have also been worn by celebrities, including actors Robert De Niro and Gerard Butler.

The company sold $8,000 of merchandise in its first year and expects more than $35 million in sales in 2010.

Power Balance, for its part, doesn't claim to have science on its side, said Adam Selwyn, a spokesman for the Laguna Niguel, Calif.-based company.

Rather, it relies on testimonials from famous athletes and users to tout the products' effects. The company says it pays some athletes for the right to use their images wearing the bracelets, including O'Neal and Odom.

Josh Rodarmel, one of the company's co-founders, said in a statement he knows there may be skeptics. "We're not trying to win over every person in the world," he said.

Ralph Reiff, program director at St. Vincent Sports Performance in Indianapolis, said maybe a third of the hundreds of professional and amateur athletes who train there wear the wristband or an imitation.

The program even thought about putting its logo on the products and handing them out, he said.

But officials decided against that because they couldn't find enough reliable research to back up the company's claims about giving a biological boost to performance, he said.

"I couldn't look in the mirror and 100 percent say (it's) a product I can put my brand reputation behind," said Reiff, a certified athletic trainer.

Reiff said he believes there's no reason to think the wristbands could produce a biological benefit, and that any benefit is purely psychological.

"It's just like a pair of lucky socks," Reiff said. "It's a lucky charm, and if you believe in it, then it's excellent."

On its web site, Power Balance features video footage of athletes holding their arms out and resisting downward pressure in trials with and without the bands.

A Wisconsin professor ran similar tests comparing the performance of 42 athletes wearing Power Balance wristbands and silicon versions from Wal-Mart and said he found no difference.

Athletes were more likely to perform better wearing the second bracelet they put on, largely because they knew what to expect from the trial, said John Porcari, professor of exercise and sport science at University of Wisconsin-La Crosse.

"I think it is a scam," he said. "It has absolutely nothing to do with the bracelets. It is all in people's heads."