介绍：The butterfly stroke is one of the most difficult swimming strokes. It is sometimes referred to as "Fly" for short. Although it is the second fastest stroke when done properly by a skilled athlete, it requires a very exact technique, strength and rhythm. It does requires a lot of practice to perfect it, but when you have it right, it is one of the most rewarding, respected and aesthetically pleasing swimming styles currently used in competition. Being able to execute a good butterfly stroke is the hallmark of a true competitive swimmer