There has to be a limit to the mental effort though. There's a point where elite athletes enter the "flow" and the mental effort disappears. Here's a video of an example in F1.
You are going to die. All the motivation that I need.
http://1.bp.blogspot.com/_5x-ImeoR2TQ/S-HaGyXa8EI/AAAAAAAABW8/UiznTlRKkP0/s1600/StillLifeWithASkull%252BPhilippe%252Bde%252BChampaigne%252B.jpg...