Streamline (swimming)

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A swimmer's transition from a platform start to a streamline position; the last figure is in a full streamline

Used most typically in competitive swimming, the streamline position is the position a swimmer takes underwater after pushing off a pool wall. To streamline, a swimmer must tuck the head into the collar bone, pointing both arms straight ahead in a tight line. The underside of both arms should be pressing on the back of the head. This position produces the most hydrodynamic position a human can take while accelerating underwater.

Kicking in the streamline position underwater can be substantially faster than swimming any of the other aquatic strokes, competitive or otherwise. For this reason, competitive swimmers often try to kick in a streamline position off a wall or the starting block for as long as they can underwater before coming up for their first stroke. The Fédération Internationale de Natation (FINA), otherwise known as the International Swimming Federation has strict regulations for underwater swimming in a FINA-regulated event. They regulate the length of the pool a swimmer may travel after the start or any turn without his/her head breaking the surface of the water, as well as the number of strokes (and, in the case of breaststroke, also the number of kicks) a swimmer may take underwater at these times.

The length one may travel underwater when racing in any one of the competitive strokes -- backstroke, breaststroke, butterfly and freestyle (typically performed as a crawl stroke) -- is 15 meters or 16.4 yards. This slightly less than two-thirds of a 25 yard or meter pool (short-course) and slightly less than one-third of a 50 meter pool (long course).^[1]

Most major competitive swimming, water polo, open water, synchronized swimming and diving events, including those at the Olympic games are affiliated with FINA. Other organizations, such as USA Swimming (formerly United States Swimming or USS), the United States' national swimming organization, have analogous rules concerning the distance a swimmer may propel underwater. USA Swimming allows a swimmer to propel no more than 15 meters (16.4 yards) underwater without the head breaking the surface in any of the competitive strokes except for breaststroke. There is no specified limit in this stroke, but, since the number of underwater strokes and kicks are regulated, this becomes a moot point to competitive swimming. It is not hydrodynamic to maintain this position past a certain distance, which is invariably less than the length of a short-course pool.

All of these regulations apply to races measured in both yards and meters and performed in both short-course and long-course pools.^[2]