Swimming is a sport [1], which is a skill of floating on water by oneself and moving forward in water by the movement of one's limbs. Swimming can be divided into competitive swimming and practical swimming. Competitive swimming is the second largest event in the Olympic Games, including butterfly, backstroke, breaststroke, freestyle and synchronized swimming. Swimming modes that are of great value in military, production and life services are called practical swimming, such as crawl (freestyle), breaststroke, side stroke, diving, treading water (vertical stroke), water rescue, military swimming and backstroke. ?