The differences in skill among athletes who compete at the highest levels of their sports are actually very small. Mere hundredths of a second are likely to separate those standing on the winner's platform from the also-rans after the Olympic 100-meter dash or 100-meter freestyle swimming competition. On any given day, the margin of victory of the world's top-ranked professional tennis player over, say, the 10th-ranked player can be just a few key points at critical moments in a handful of key games. The difference between being ranked number one and number ten is likely to be not just raw ability but the consistency with which a player exercises that ability from game to game, even point to point, during a match.

In this highly competitive environment, athletes look for any edge that will help them win. To achieve that end, they have enlisted...