How to swim the butterfly stroke?
As odd as it may seem, the butterfly stroke is similar to the swimming of dolphins because the legs perform undulating movements, as opposed to the scissor movements of the crawl, for example.
For beginners, the most common difficulty is in returning the arms forward through the air. This requires coordination between the return of the arms and the second undulation of the legs.
And the legs themselves must be held together during the entire stroke. They must undulate, extending the movement of the upper body.
The upper body is also very much in demand, starting with the arms. Indeed, it is essential since it is the arms that exert the traction and thrust which propels the body forward.
Finally, breathing is the most important point. It can be done with each arm movement for distance or with every two or three strokes of the arms for speed, which requires even more relaxation and coordination. The hardest part for the beginner is to perform correct undulations in order to balance arm movements with breathing.