Swimming is an individual or team sport that involves using arms and legs to move the body through water. Typically, the sport takes place in pools or in open water (e.g., in a sea or lake). Competitive swimming is one of the most popular Olympic sports, with events in butterfly, backstroke, breaststroke, freestyle, and individual medley. In addition to these individual events, swimmers take part in relays. Swimming each stroke requires specific techniques, and in competition, there are specific regulations concerning the acceptable form for different strokes. There are also rules put in place to regulate what types of swimsuits are allowed at competitions. Although it is possible for competitive swimmers to incur several injuries from the sport, there are also multiple health benefits associated with the sport.HistoryEvidence of recreational swimming in prehistoric times has been found, with the earliest evidence dating to Stone Age paintings from around 10000 years ago. Written references date from 2000 BC, with some of the earliest references to swimming including the Iliad, the Odyssey, the Bible, Beowulf, the Quran and others. In 1538, Nikolaus Wynmann, a German professor of languages, wrote the first swimming book, The Swimmer or A Dialogue on the Art of Swimming (Der Schwimmer oder ein Zweigespräch über die Schwimmkunst).