Swimming stroke

Human swimming typically consists of repeating a specific body motion or swimming stroke to propel that body forward. There are many kinds of strokes, each defining a different swimming style or crawl.

Most strokes involve rhythmic and coordinated movements of all major body parts — torso, arms, legs, hands, feet, and head. Breathing typically must be synchronized with the strokes, too. It is possible however to swim by moving only legs without arms or only arms without legs; such strokes may be used for special purposes, for training or exercise, or by amputees (paralympians) and paralytics.

A number of strokes are only used for special purposes, e.g. to manipulate an object (a swimmer in distress, a ball), or just to stay afloat.

Any style with underwater recovery can be swum under water for certain distances depending on the need for air. Underwater swimming on the back has the additional problem of water entering the nose. To avoid this, the swimmer can breathe out through the nose or wear a nose clip. Some swimmers can close their nostrils with the upper lip or with the compressor naris muscles.

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Wikipedia