LONDON Cristiano Ronaldo wears one. Rubens Barrichello swears by his. And it has been endorsed by the entire Wasps rugby team. Indeed, though it looks like a slim band of silicone inset with two flimsy holograms, an increasing number of sports stars are claiming that they can increase their balance, strength and agility simply by wearing something called a Power Balance bracelet - on sale for the princely sum of GBP29.99 at a sports shop near you.

“I don't usually do a lot of testimonials,” says superstar American basketballer Shaquille O'Neal, “but this works.” He recounts the first time he wore the bracelet in a match “We won that game by 57 points.” Grand Prix driver Barrichello is similarly effusive. “The first time I used it in a race,” he says, “I won.” Spain's World Cup winning team are also fans, while the two finalists at this year's Queen's tennis championships were both sporting one.

So how does this snake oil - sorry, accessory - work? The makers of the Power Balance are vague. It's something to do with that hologram, made from the reflective plastic Mylar, “optimising the body's natural energy flow”. They “prove” the band's effectiveness by pressing down on a volunteer's arm; once the volunteer dons the bracelet, their arms supposedly become more resilient, because the band is “designed to resonate with and respond to the natural energy field of the body”.

Aren't we just talking about a cheap wristband here? Er, yes, say a group of researchers in Australia, where the band has been heavily marketed. Australian Skeptics argue that the band merely has a placebo effect - and they carried out a series of tests on its Australian distributor to prove it. Power Balance's Tom O'Dowd was challenged to identify which person in a group of six had the band concealed on them, using the “pressing down” technique described earlier. O'Dowd failed - five times out of five.

Sports psychologists aren't surprised. Bruce Hood, a professor in psychology at Bristol university, believes that any scientific explanation for the Power Balance is “wishful thinking”. He says he is “unaware of any plausible scientific mechanism whereby holograms could have measurable effects on the body.” Meanwhile, Victor Thompson, a sports psychologist who runs the website SportsPsychologist.co.uk, suggests the Power Balance plays merely on the superstitions of its users “It gives people the expectation that they'll play better. And if you're expecting to play better, then you probably will.”

Ever the arbiter of fair play, I went to the Royal Opera House to see if one of the Royal Ballet's dancers could detect any Power Balance-based advantages. Claire Calvert, a first dancer who will be performing in Onegin this autumn, slipped on the wristband. She stretched, she pirouetted, she did some arabesques. And did she feel better balanced? She laughed. “I don't think I feel a difference!”—Dawn/The Guardian News Service