What it is
An effective butterfly kick in which the body rolls and flows like a constant sine wave, with all movement against the water. A whole-body undulation that propels the swimmer forward like a dolphin.
Essentials
- Keep the body rolling and flowing like a constant wave; the motion is continuous and unbroken from chest to toes.
- The kick starts with the chest pushing forward; the stomach and hips follow, the knees snap the legs, and the pointed feet snap, flow, and move the most.
- All movement is against the water — chest, stomach, hips, thighs, knees, feet.
- Keep the feet close together; legs and feet move as one unit, as if glued from the thighs to the ankles.
- Drive the movement with the hips: flex the quads and hamstrings, squeeze the belly.
- Press the chest forward to create a divot in the lower back, then fill the lower back and retreat the chest.
Progression
- Use the whole body in soldier position (arms at the sides) to begin.
- Build from soldier kicking to doing the fly kick in streamline underwater.
- Add fins to give power to the kick, but always combine fin work with no-fin kicking.
What goes wrong
- The chest does not initiate the kick; the hips or legs take over. Correct by cueing the chest to push forward first.
- The head bobs or the arms doggy-paddle. Keep the head still; use doggy paddles only as a beginner aid for forward motion, not as part of the kick itself.
- The legs separate or the feet splay. Keep the feet close together and move the legs and feet as one unit from thighs to ankles.
- Movement is passive or slides through the water instead of pushing against it. Every segment must press against the water.
- The wave breaks or stalls mid-body. Watch for a continuous, unbroken rolling wave from chest through the body to the toes.
How you know it worked
The swimmer produces a continuous, unbroken sine-wave motion from chest through toes, with every segment moving against the water, and propels forward like a dolphin.
How you teach it
Demonstrate the fly kick in the water for the best results; most swimmers, young and old, learn the kick best by watching someone do it and then attempting it on their own. Begin with the whole body in soldier position so the learner feels the full undulation without the added complexity of arm position. Fins are useful here: they give power to the kick and help teach breathing, strength, and the need for flowing constant motion, but always pair fin sets with no-fin kicking so the swimmer does not become dependent on the extra surface area.
At the pool edge, your feedback is observational: watch that the chest initiates each kick, that the stomach and hips are actually moving (not just the legs), that the knees snap, that the feet stay pointed and move the most, and that the entire wave is against the water rather than through it. The cue "press the chest forward to create a divot, then fill the lower back and retreat the chest" is the single most diagnostic check — if the lower back never fills, the wave is not travelling. For beginners who cannot yet generate forward motion, allow doggy paddles to keep them moving while they focus on the body wave, but challenge them to keep the head still and to stop using the arms as soon as the undulation produces its own propulsion.