COMPETITIVE swimming（竞技游泳） has the goal of maximizing（最大化） performance, usually the speed of swimming. The International Swimming Federation(FINA)（国际游泳联合会） has four swimming areas, with different distances.
In freestyle（自由泳）, there is no certain action, except in the freestyle part of medley swimming（接力赛）. In practice, almost all freestyle events are done using the crawl（爬泳）.
In butterfly（蝶泳）, the swimmers have to move the two sides of their body in exactly the same way. They have to move their arms at exactly the same time.
In breaststroke（蛙泳）, swimmers have to push their hands forward together. They must keep elbows （肘） under the water.
In backstroke（仰泳）, swimmers have to lie on their back at all times, except during turns, to perform the stroke. It is like an inversion（倒置） of the crawl — swimmers swing their arms alternately（交替地）, and pull them through the water, and use a flutter kick（浅打水）.
