Interesting National Geographic article on the things that make Lance Armstrong the winner that he is:

Early in his career Armstrong showed only average muscle efficiency—the percentage of chemical energy that the muscles are able to harness to produce power. Higher muscle efficiency means greater production of power.

From 1992 to 1999, the year of his first Tour de France win, Armstrong was able to increase his muscle efficiency by 8 percent through hard and dedicated training. Coyle says Armstrong is the only human who has been shown to change his muscle efficiency.