Phelps, who won six gold medals at the 2004 Athens Games, has spent the past four years training with Club Wolverine in Ann Arbor.

He is on the cusp of history for many reasons: his tolerance for pain, his lung capacity, his desire to win, his training, his coaching.

But where Phelps is different, where he stands alone among world-class swimmers, is how he is built, which, in turn, allows him to undulate through the water in what most swimming experts refer to as the best butterfly stroke in history.

Phelps is 6-feet-4 and 195 pounds. His torso is long and slightly concaved. His back is slightly bowed. His legs are short and hyperextended. In other words, they are ridiculously flexible.

All of this does a few things. First, the hyperextension allows for greater reach, which means he can displace more water than just about anyone else. This is especially true in his ankles, which are like flippers. Second, his huge torso acts as a hull of a boat, which allows him to ride on the water.

And lastly, his reach lets him grab more water. In fact, his arm span is longer than his height - by three inches. Most people's span is the same as their height.

As Phelps rises from the water during the fly, thrusting himself with his dolphin kick helped by those freakish, double-jointed flippers, his hands and arms casually move across the top of the water during recovery before digging back in out front. And he keeps them low. It is as fluid and gorgeous a movement as there has ever been in swimming.

 "This is the best specimen that nature has come up with in terms of swimming," Stewart said. "We've never seen anything like him."

Like a fish.

Or, more accurately, like a dolphin

By SHAWN WINDSOR • FREE PRESS SPORTS WRITER • August 13, 2008