Why Michael Phelps is changing his stroke.

The stadium scene.
May 20 2009 12:24 PM

Why Is Michael Phelps Tinkering With Success?

Wasn't his old stroke good enough for Olympic gold?

Michael Phelps. Click image to expand.
Michael Phelps

In his first meet since completing a three-month drug suspension, Michael Phelps tried out a handful of new events. The results, in the 100-meter backstroke and the 50-meter and 100-meter freestyle races, were unusual for the usually infallible Phelps: He lost. For the swimming star, though, winning wasn't the primary goal. In the freestyle races, he was trying out a new "straight-arm" technique. Why would the most successful swimmer in history change the way he swims?

Because he wants to be a sprinter. Looking for a new challenge, Phelps has replaced some of his old-standby events with sprints "just to say [he's] done it." The new events require entirely different skills and strategy. Phelps has dominated the 200-meter freestyle for years by finishing stronger than his competitors, often surging past the field (or extending his lead over the hapless also-rans) in the back half of the race. The 100-meter freestyle is totally different, favoring powerful swimmers who go full throttle for only 48 seconds.

In terms of explosive speed, the straight-arm technique has a couple of advantages. Traditionally, freestylers bend their recovery arm—the one that's not in the water—keeping the elbows above the hands. The newer technique, which Phelps used only intermittently in this past weekend's UltraSwim meet, gives the impression of a semi-submerged windmill. A traditional recovery arm is still moving forward when it touches the water. The water slows the hand down and prolongs recovery time, resulting in fewer strokes per minute. A straight recovery arm transitions more quickly to a propulsive stroke because the hand is moving down and back toward the feet almost as soon as it touches the water.

The straight arm also offers rotational advantages. Freestylers don't swim on their stomachs; they knife through the water on one side, then the other. The more quickly they rotate their shoulders, the faster they move forward. The straight recovery arm creates torque on their torsos, turning the swimmer into a flywheel. "Think of a baseball pitcher," says Glenn Mills, a former Olympic swimmer and founder of a popular swim technique Web site. "The windup and kick create a rotation that whips the throwing arm forward." In swimming, "when you throw the extended recovery arm over, it helps turn the torso and pulls the other arm back out of the water."

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Most biomechanics coaches agree that the straight-arm technique is potentially faster. The problem is that it requires much more power. The quicker transition from recovery to propulsion means the swimmer's arms must drive through the water that much faster. The swimmer also expends significant energy swinging his recovery arm through the air. Very few swimmers can maintain that level of output over 100 meters. (This may explain why Phelps alternated between his old technique and the new one in last weekend's 100-meter final.)

It's also difficult for anyone to maintain proper form when he is working that hard. "Remember," says Russell Mark of USA Swimming, "the propulsive arm is still doing most of the work. If your form under the water suffers, there's no advantage to a straight-arm recovery."

Phelps is far from the first to adopt the technique. It was popularized in the 1990s by David Marsh, then the swim coach at Auburn University. It's gaining in popularity as modern suits, which are more buoyant and produce less drag, enable more swimmers to maintain the stroke. Still, only the most powerful swimmers are having success with it. Fred Bousquet, the muscular French freestyler and Auburn alum who beat Phelps last weekend, uses the straight arm. Many suspect that Phelps' dabbling with the new technique means he will soon look more like Bousquet: bigger, stronger, and more powerful. While he has dropped 20 pounds since ballooning to 205 pounds during his drug suspension, most observers note that he has added muscle.

Brian Palmer writes about science, medicine, and the environment for Slate and Earthwire. Email him at explainerbrian@gmail.com. Follow him on Twitter.

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