The Ionic Man - Will a Vest Decide Who Wins Rugby's Biggest Prize?

IonX is a new shirt with an ego so large it's a wonder that it deigns to be worn on your back at all.

This boastful piece of polyester and elastane is the latest piece of kit that may propel England to rugby glory. And if it doesn't, then the same magic fabric worn by Australia, South Africa, Ireland, Scotland and Japan will surely be a World Cup winner.

The competition started last night, and with England - the defending champions - playing their first match later today, the pundits believe the cup holders will need all the help they can get if they are to triumph once again.

Shirts used to be jerseys. Then they promised to keep you hot or cool, or efficiently dispel your sweat. Now IonX, developed over three years by New Zealand-based kitmaker Canterbury, claims to deliver "ionic" energy to the body through a negatively charged electromagnetic field.

Eh? You may think it's easy to sell shirts to large men suggestible enough to bury their heads in each others' thighs for 80 minutes, but the manufacturers claim to have created a fabric coated in a liquid wash that when placed against the skin creates a negative charge of ions.

Ionization, and the physical benefit of negative ions, has a slightly shady history: during the second world war German scientists placed bombers in ionizing chambers to increase their strength.

Athletes in the Soviet Union later used ionization in the spirit of cold war competitiveness.

It is claimed that research suggests this negative charge helps increase blood flow and the supply of oxygen to the muscles, enabling them to work harder, recover more quickly and get rid of waste products that build up in exercise, such as lactic acid.

Can a shirt really do this, or is it pseudo-scientific gobbledegook? IonX is backed by one piece of scientific research funded by Canterbury: Mike Cain of Loughborough University found the shirts delivered a 2.7% improvement in athletes' "peak power" in short bursts of high impact exercise on cycling machines.

Dr Cain is cautious about the benefits and admitted that more research needs to be done. Although his testing of the shirts was funded by Canterbury, he insisted that his "independence is critical to the credibility of what we do". He will publish a paper on the 2.7% finding, a "statistically significant improvement", at a sports science conference in Singapore next month.

Meanwhile, the Guardian thought it would rigorously test IonX by making its least-likely-to-excel-at-rugby reporter run up London's steepest hill. Taking Dr Cain's advice, I put on the tight, white IonX base layer (as worn by the England players), a snip at £45, half-an-hour before beginning.

For decorative effect, I put a Scotland IonX shirt over the top. Dr Cain said an extra shirt would make no difference - what matters is that one of these shirts is tight against your skin. Slightly rubbery and as snug as a wetsuit, the shirt felt like it was trying to throttle me. It was also very warm. But hang on, as I struggled up the hill I felt different. The suggestible bit of my brain concluded that yes, the blood seemed to be pumping round my puny upper body with a bit more vigour than usual.

Did I feel 2.7% better? Hell yes! Although maybe that was just because it was a pleasant afternoon out of the office. They say that tiny advantages can snatch victory from defeat in professional sport. But amateurs like me could easily find a 2.7% improvement in running up that hill by forsaking the lunchtime curry. And modern sports science would probably vouch for another 2.7% improvement if I hadn't got a hangover.

From "Fastskin" swimsuits to those plasters that footballers briefly put on their noses, sports stars and big brands have short-lived infatuations with new technology. Will IonX stand the test of time? If those nations not wearing the technology - France or New Zealand - win the World Cup, the world's most boastful shirt may shout a little less loudly.