MICHAEL PHELPS AT 30 m OF HIS WORLD RECORD GOLD MEDAL 200 m BUTTERFLY RACE AT THE 2007 WORLD CHAMPIONSHIPS IN MELBOURNE
Each frame is 0.1 seconds apart. Michael Phelps' world-record time for this event was 1:52.09.
This stroke analysis includes a moving sequence in real time, a moving sequence where each frame is displayed for .5 of a second, and still frames.
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The kick (the surfaces of the lower legs and feet) has served to counterbalance the vertical force component created by the arms entering the water and the head and shoulders reentering. The kick does not serve a propulsive purpose but simply allows the swimmer to continue as streamlined as possible in this phase of the stroke.
At this stage, the swimmer is "riding" forward solely on momentum developed much earlier in the propulsive stages of the underwater arm action. The progression exhibited here is one of negative acceleration because no propulsive forces are developed.
The position of the hips being higher than the head is a necessary artifact of the butterfly stroke. They have to be high so they can counterbalance the raising of the shoulders and head to breathe, which Michael Phelps does every stroke. If the hips were not elevated, but level with the head, then when the head and shoulders rose, the hips would sink very deep and cause a significant increase in frontal resistance at the critical stage of developing arm propulsion.
An admirable feature of Michael Phelps' breathing action is that it incorporates hyperextension of the upper spine. That results in the hips remaining on the surface and the arms providing all the counterbalancing that is necessary for the shoulders and head to rise. The spinal action is similar to that which has emerged over recent years in the breathing actions of most top breaststrokers.
The position and amount of drag turbulence on the back of the lower legs and the souls of the feet (Frame #9) shows that Michael Phelps' leg kick is not propulsive at all. It generates only vertical forces that counterbalance the vertical force components of the arm movements in the latter stage of the underwater arm action. The kick starts at this time in the stroke because the arm action is starting to "round-out", that is, it increasingly develops a greater vertical force component as the approach to and execution of an exit occurs.
The depth of the kick at the feet is quite shallow and level with, or marginally below, the streamline of the total swimmer (as shown clearly in Frames #11 and #12).
Michael Phelps is vastly superior to all other 200-m butterfly swimmers, winning this race by more than three seconds, which is an "unheard of margin" in world championship swimming over the 200-m distance. He has some very noteworthy characteristics about his stroke: 1) the length of time in streamline, 2) the shallowness of both kicks, and 3) the hyperextension of the upper spine to facilitate breathing. He probably has a naturally endowed physique that moves through water with less resistance than most other swimmers, and a very good physiological engine suited to 200-400 m swimming events. One is struck by the simplicity of Phelps' stroke. He performs no extraneous or exaggerated actions. One could hypothesize that he should breathe every other stroke although the rhythm of every-stroke breathing might facilitate better oxygen utilization (i.e., it is his most economical movement cadence) than could be achieved by holding the breath longer with double-stroke breathing. Only detailed accurate measurements of a considerable number of physiological and biomechanical factors could resolve questions about his butterfly stroke.
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