Swimming is the movement of the body through water using arms and legs. Most of the time equipment is not used. People swim for exercise, fun, and they can swim competitively. People swim using their arms and/or legs. There are several "strokes": breaststroke, front crawl, butterfly, and backstroke are some of them. The main stroke usually is front crawl, but many people prefer breaststroke because it is relaxing. Swimming can be done for competitive sport. Many schools use swimming as a physical training exercise. Some swimming is just for fun, like doing backflips under the water. People can swim in the sea, swimming pools, rivers and lakes. Swimming has been around for a long time. Humans learned how to swim from the sea creatures. When they started swimming, they could swim as well and fast as today. Swimming works all the muscles simultaneously. It is impact free.