The fixed-gear bike means the Toughest Guy in the World can never stop pedaling. His legs must perpetually trace perfect circles; straining so hard on the uphill it looks like grapefruits have been sewn into his calves, whirling so fast on the downhill it seems as if any minute they might spontaneously combust.

He will do this for 6 1/2 punishing hours, for 120 leg-pounding, back-screaming, butt-throbbing miles. He will do this today just as he did it yesterday. As he will do it tomorrow and the day after that.

Some days he will do it on the fixed-gear. On others, he will ride his more conventional, 20-gear bike. But he will ride. He will ride to train his muscles, to forge his lungs, to flog himself into an ever higher realm of fitness, the realm of Olympic gold medalists and the even more rarefied realm of those who refuse to let shattered bones prevent them from triumphing in the most boiling crucible in all of sport.

But these days, the Toughest Guy in the World also does it for another reason. He rides to distract himself from the very real scenario that all this arduous training might be for no reason at all.

And so if it seems that Tyler Hamilton - he of the altar boy face and the soul full of grit and tenacity - rides as if his life depended on it. Well, in a way, it does.

Today is the first day of the Tour de France, the world's most grueling cycling race - perhaps the world's most grueling athletic event. But for th