The 23-year-old US swimming star says he is stronger both physically and mentally as he prepares for another assault on Mark Spitz's record of seven gold medals at one Games.

He fell short of that goal in Athens four years ago, coming away with a still impressive six gold medals and two bronze, but insists those who say eight golds are impossible - including Aussie great Ian Thorpe - are wrong.

"If you think about doing the unthinkable, you have a good chance of doing that," says Phelps, who is qualified to swim five individual events and three relays in Beijing.

Phelps will spearhead the US challenge in what is certain to be another pitched pool battle with perennial powerhouse Australia.

Both nations face an ever-increasing challenge from a raft of superb swimmers from around the globe.

"We try not to focus just on Australia, because the challenges are coming from everywhere," US women's head coach Jack Bauerle said.

All will have to find a way to cope with an unfamiliar format of morning finals and evening heats in the National Aquatics Center, dubbed the Water Cube, where the 32 swimming events, diving and synchronized swimming will be held.

The high-tech building, sheathed in a Teflon-like outer membrane that resembles water bubbles, will provide a fitting backdrop for a controversial new piece of swimming technology - Speedo's LZR Racer swimsuit.

Swimmers wearing the form-fitting bodysuit set more than 40 world records (long course and short course) in the first four months since it's release in February.

While the manufacturer insists it is impossible to confirm reports that it reduces times by up to two percent, the feeling that the LZR offers a clear competitive advantage sparked a stream of defections from other suppliers by swimming medal hopefuls and a race by rival manufacturers to come up with a similar product.

One of the high profile converts to the LZR is Japan's double Olympic champion Kosuke Kitajima, who said he would wear the suit in Beijing after the Japanese Swimming Federation dropped a requirement to wear domestic products.

Kitajima, who will defend the 100m and 200m breaststroke titles he won in Athens, shattered the 200m breast world record when trying out the Speedo suit.

While debate raged over whether the swimsuits offer an unfair advantage to those who wear them, American Natalie Coughlin insisted the pre-Olympic spate of records was not a mere triumph of technology but a sign of the spectacle that the world's top swimmers were preparing to deliver in Beijing.