Science has figured out one of the reasons Michael Phelps is so dang fast. A series of studies completed since the Beijing Olympics has radically challenged some long-held conventional wisdom about swimming, Reuters reports. One study funded by USA Swimming, for instance, found that when it comes to freestyle and backstroke, a paddle-like "deep-catch" stroke generates more speed than the more popular "sculling" stroke, in which the arm enters the water vertically and cuts in toward the body then back out, making an "S" shape. Phelps employs a modified deep-catch stroke.
In another, perhaps even more revelatory study, a Duke mechanical engineering team found that it's actually more efficient for freestyle swimmers to slightly spread their fingers, rather than forming a tight cup with them. Swimmers have always assumed a cupped hand would provide more force, but computer modeling showed that some water actually sticks to, and moves with, your fingers, thanks to the so-called "boundary layer" effect. So a swimmer who can spread his fingers a slim one-fifth to two-fifths of their diameter could enjoy up to 50% more force.