Butterfly will exercise the muscles of shoulders, waist and abdomen, breaststroke freestyle will exercise the muscles of legs, breaststroke is the thigh, freestyle is the thigh and calf, backstroke will not exercise too many muscles compared with the other three. If it is intensive training, it will not lose weight, but will only turn fat into muscle and become stronger and stronger. If you just relax yourself, it is recommended to choose freestyle, which can exercise your body curve, but the movements should be standard, otherwise it will have no effect.