1. The power to swim back. When backstroke, the extensor dorsi will exert more force and stretch the back muscles. In addition, when backstroke, you need to lift your hips and slide, which is also an exercise for your hips. 2. arm strength. In freestyle, the biceps brachii and triceps brachii of the upper arm exert more force, which can effectively exercise the arm muscles and improve the shoulder muscle strength. 3. Leg strength. Both freestyle and backstroke are whipped up and down, and only breaststroke is a pedal clip. The former can make legs more slender, and the latter uses quadriceps femoris more, so it is very effective for strengthening leg strength. 4. Butterfly power. In butterfly stroke, the arm strokes inward, which is similar to chest expansion. Exert more force on pectoralis major, extensor dorsi and rectus abdominis, and the exercise effect is also the best.