Go Swim Straight-Arm Freestyle with Scott Tucker from Glenn Mills on Vimeo.
Glenn Mills:
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." - source
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." - source
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