I suppose it depends at how you want to define athelete. If you are looking at endurance, it is hard to beat what Lance has acomplished. Riding a bike up a mountain for 100 miles in like 4 hours is just unimaginable. Micheal obviously can outjump Lance, but then again there have been basketball players who can jump higher than Micheal.
Probably "endurance under handicap" could be a good criterion, even under a self-inflicted handicap. There was Alexander Alekhine who used to play multiple simultaneous chess games [at his grandmaster level] while seriously drunk.