Butterfly has a reputation problem. Most swimmers believe it belongs to big shoulders, and that if you are not built like a sprinter you should leave it alone. I raced the 200 individual medley at two Olympic Games, and the medley opens with butterfly, so this stroke has taken up a large part of my life. What it rewards is not strength. Strength buys you about 25m of survival. Rhythm is what lets you swim it.
The butterfly I see most often on a public lane is a fight with the surface: the swimmer climbs, the arms come over late, and by the second length they stop clearing the water. That is a timing problem, not a fitness problem, and timing is learnable at any age.
Why is butterfly so exhausting?
Because it is the stroke where slowing down between strokes costs the most, and almost everyone slows down too much. You do not swim at a constant speed: you accelerate while your hands press water backwards and decelerate as soon as they stop. Researchers call that within-stroke fluctuation dV, and a review chapter on the biomechanics of competitive swimming strokes states the consequence directly: "increasing dV will lead to an increase in the energy cost of swimming, even controlling the effect of the v", where v is your average speed. Two swimmers can hold the same pace, and the one whose speed collapses between strokes pays more for it.
Butterfly makes that collapse bigger than any other stroke, because both arms leave the water together and nothing pulls you forward during the recovery. Every fault that costs you speed is twice as expensive here. The stroke feels like a fitness test when it is really an efficiency test.
How do the two kicks fit into one arm cycle?
One kick lands as your hands enter the water, the second as your hands finish the pull and come out. That is the whole skeleton of the stroke, and getting those two moments right fixes more than strength work ever will. The same chapter describes what a cheap butterfly cycle looks like: "At Butterfly stroke, a low velocity during hand's entry, a high hand's velocity during the upsweep and a high velocity of the second downbeat will decrease the dV". In plain language, enter softly, accelerate your hands towards the end of the pull, and kick hard as they exit.
A pilot study that measured hand and foot velocities through the cycle put the point about the legs plainly: "downbeat actions are clearly connected to propulsion through lower limbs actions, in Butterfly stroke", in research on segmental velocities in butterfly. Self-taught butterfly usually has one usable kick, or two apologetic ones of the same small size. The second kick carries you through the recovery, so build that one first. If your dolphin kick has no snap at all, the ankle work in my post on the freestyle kick applies here too.
Where should my hands enter in butterfly?
About shoulder width apart and in front of the shoulders, going forward into the water rather than slapping down onto it. Wide entries turn the first part of the pull into a sweep that holds nothing, and narrow entries put your hands under your face where you have no leverage. Press out slightly, sweep in under your chest, then accelerate back past your hips.
The accelerating part matters more than the shape. The butterfly study above concluded that "The hand's velocity in the most propulsive phases of the stroke cycle seems to be a determinant variable for the behavior of dV, at different swimming velocities". A stroke that feels smooth but never speeds up at the back end leaves its propulsion in the water. Same principle as in freestyle hand entry, just twice as unforgiving.
Why do my hips sink when I swim butterfly?
Because your chest rides too high and your head stays up too long, which tips your trunk and turns your body into a wall. The biomechanics chapter is blunt about the cost of that angle: "Higher trunk angle with horizontal plane will increase the projected surface area and the drag force." Every centimetre you climb is paid for by your hips dropping behind a bigger obstacle.
The fix is not to swim flat. Press your chest forward and slightly down as your hands enter, so the wave travels along your body instead of pivoting it. That undulation is the same movement that drives breaststroke, which is why medley swimmers learn both together. If your lower back is sore afterwards, the wave is coming from your spine rather than your hips, the same mechanism I describe in lower back pain in breaststroke.
When should I breathe in butterfly?
Late in the pull, low to the water, with your head back down before your hands enter. Your chin should barely clear the surface, pushed forward rather than lifted, and your eyes should look at the water just ahead. If your head is still up when your hands land, your hips are already sinking for the next cycle.
How often you should breathe is genuinely unsettled, and anyone giving you a hard rule is guessing. Some swimmers breathe every stroke, some every second one. What is not negotiable is the cost of a badly timed breath, since lifting the trunk raises drag exactly as the sentence above describes. Learn the stroke breathing every second cycle, then experiment once the rhythm holds.
How fast should I swim butterfly in training?
At a real rhythm over short distances, never slowly over long ones. Slow butterfly is harder than properly paced butterfly, because a slow undulation gives the second kick nothing to work with. A small study of eight young male swimmers found that "The swimming speed was predicted by a combination of the stroke frequency and thrust (R2 = 0.84, p = 0.010)", in work on kinematics and kinetics in the butterfly stroke. Eight swimmers make that a hint rather than a law, but it matches the deck: tempo and force go together, and killing the tempo kills the stroke.
So swim butterfly in 15m and 25m pieces with generous rest, and stop the set the moment the shape falls apart. Six good lengths beat twenty ugly ones. For the freestyle around it, the swim pace calculator gives you sensible target times, and my guide to swimming without getting tired covers pacing the session as a whole.
A butterfly drill set that actually transfers:
- 8 x 25m body dolphin on the surface, arms at your sides, feeling the wave start at your chest
- 6 x 25m three dolphin kicks then one full stroke, so the two kicks have room to separate
- 6 x 25m single arm butterfly, other arm extended forward, breathing to the front
- 8 x 15m full butterfly from a push, 30 seconds rest, stopping when your arms stop clearing the water
- 4 x 25m butterfly kick on your back, which shows you instantly whether the wave comes from your hips or your knees
- Once a week, 25m butterfly then 75m freestyle continuous, so the stroke survives a little fatigue
- Fins are fine on the kicking drills and a bad idea on full stroke, since they hide the timing
Outside the current supported analysis: butterfly. SwimRead is a swimming video review app, currently in beta. It supports short, side-view freestyle recordings, shows which automatic measurements are available, and keeps a history and chosen training focus for each swimmer. It does not grade technique or establish that a specific error was detected. Video stays on the phone; technical measurements and body-landmark coordinates are sent as described in the Privacy Policy. Join the beta waitlist for an invitation as places open.