you can not expect a player who runs 40 yard fly routes play after play to sprint at 100% every single play even when he knows he has no chance of getting the ball.
Interesting you would make that point. A reporter a couple years ago (when Moss made his comments) asked Rice if he went 100% every play. His response was yes. He knew he was in better shape than the DBs covering him, and at the end of the game, they would be tired and he'd beat them.