Undulating through the water in porpoise-like fashion, swimming the butterfly stroke requires impeccable timing backed up with sheer strength. As graceful as it looks, the butterfly is the most difficult of the strokes to master, requiring specialized strength training and diligent practice. The powerful two-legged kick propels the swimmer forward to raise both head and arms out of the water to position for the next stroke.
Position Your Body
The basic body position for the butterfly is a prone position with your face in the water. Stretch your arms out straight in front of you along the top of the water with your fingers almost touching. A good way to get a feel for proper body position in the water is to propel yourself forward by undulating your body with your legs close together. Try it first with your arms at your side, as this is easiest. After you get the hang of it, extend your arms out in front of you, raising your head to take a breath after several kicks. Separate your hands so they are about shoulder width apart and press down slightly as you are breathing. This not only helps the mechanics of getting a breath, but is the same way you'll begin the arm stroke.
Kick From The Core
The powerhouse kick for the butterfly involves the lower half of your body from your chest to your toes. As you are floating face down in the water, press your chest a few inches towards the bottom of the pool and release. As your chest comes back up, drive your hips downward. Follow this movement by pressing toward the bottom of the pool with your thighs, allowing your knees to bend slightly. This will drive your hips upward. Follow through with the lower legs and the top of the feet in a whipping motion. Practicing this kick while wearing flippers helps you get a feel for the proper technique as you build muscles vital to a powerful kick.
Fly With Your Arms
The initial part of the butterfly's arm movements take place beneath the surface of the water. Begin in a downward-facing prone position in the water with your hands extended out in front of you. Allow your hands to separate to about shoulder-width and pull your hands toward your waist simultaneously. As your hands pass your chest, the stroke changes from a pull to a push, and you can raise your head to breathe. Thrust the water forcefully toward your hips, keeping your elbows pointed out to the side. Recover your arms simultaneously above the water as you undulate and kick powerfully. As your arms re-enter the water ahead of you, tuck your face back down in the water.
The simplest way to get good at the butterfly stroke is to practice, practice, practice. Try replacing every other lap of your workout with the butterfly. Stand-up paddleboarding can provide you with some time away from the pool while continuing to build upper back, arm and core strength. Resistance training provides another way to build strength. Use exercise bands or a cable resistance machine while lying on your back to do a double arm pulldown from above your head to thigh level. While pulling down, simultaneously do double leg raises to build arm, leg and core muscles you'll need for the butterfly stroke.