Dolphin kick

The butterfly (colloquially shortened to the fly) is a swimming stroke swum on the breast, with both arms moving symmetrically, accompanied by the butterfly kick (also known as the "dolphin kick"). While other styles like the breaststroke, front crawl, or backstroke can be swum adequately by beginners, the butterfly is a more difficult stroke that requires good technique as well as strong muscles. It is the newest swimming style swum in competition, first swum in 1933 and originating out of breaststroke.

The peak speed of the butterfly is faster than that of the front crawl, or freestyle due to the synchronous pull/push with both arms and legs. Yet since speed drops significantly during the recovery phase, it is overall slightly slower than front crawl, especially over longer distances. Another reason it is slower is because of the extremely different physical exertion it puts on the swimmer compared to the freestyle.

The breaststroke, backstroke, and front crawl can all be swum easily even if the swimmer's technique is flawed. The butterfly, however, is unforgiving of mistakes in style; it is very difficult to overcome a poor butterfly technique with brute strength. Many swimmers and coaches consider it the most difficult swimming style. The main difficulty for beginners is the synchronous over-water recovery, especially when combined with breathing, since both arms, the head, shoulders and part of the chest have to be lifted out of the water for these tasks. Once efficient technique has been developed, it becomes a smooth, fast stroke.

Australian Sydney Cavill (1881–1945), son of the "swimming professor" Frederick Cavill, was 220 yards amateur champion of Australia at the age of 16 and is credited as the originator of the butterfly stroke. He followed his famous brothers to America and coached notable swimmers at San Francisco's Olympic Club.

In late 1933 Henry Myers swam a butterfly stroke in competition at the Brooklyn Central YMCA. The butterfly style evolved from the breaststroke. David Armbruster, swimming coach at the University of Iowa, researched the breaststroke, especially considering the problem of drag due to the underwater recovery. In 1934 Armbruster refined a method to bring the arms forward over the water in a breaststroke. He called this style "butterfly". While the butterfly was difficult, it brought a great improvement in speed. One year later, in 1935, Jack Sieg, a swimmer also from the University of Iowa, developed a kick technique involving swimming on his side and beating his legs in unison, similar to a fish tail, and then modified the technique afterward to swim it face down. He called this style Dolphin fishtail kick. Armbruster and Sieg quickly found that combining these techniques created a very fast swimming style consisting of butterfly arms with two dolphin kicks per cycle. Richard Rhodes claims that Volney Wilson invented the 'Dolphin' after studying fish, and used it to win the 1938 US Olympic Trials, earning him a disqualification.

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