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Take Home Points on Kick Timing in Butterfly

  1. The kick helps counteract the actions of the arms and orients the body horizontal, an ideal position for forward propulsion.
  2. The first kick occurs at the arm entry.
  3. The second kick occurs at the arm exit. 
Many realize swimmers do not pull their arm past their body, but anchor their arm and move their body past their arm. Despite this knowledge, implementing this strategy is difficult, especially on butterfly. Now, everyone around a pool deck has heard the comment “anchor the arm, then swim past it”, but often times this cue falls short of improvement.

In swimming, understanding physics may help highlight ideal biomechanics. For me, physics and knowledge of forces helped me understand a “hip-driven” freestyle stroke and is now unlocking the idea of swimming past my arms on butterfly. Before you move on, make sure to read “How to swim the butterfly” for an indepth review of butterfly biomechanics. This piece goes over a lot of information, yet the timing of the kick and role of the kick with the catch is absent, a vital flaw. The kick, as written, should be small and fast. Ideally, the kick helps counteract the actions of the arms and orients the body horizontal, an ideal position for forward propulsion.

First Kick

Just before hand entry, the first kick occurs. This motion helps counteract the action of the arms, but also raises the hips and body for the first propulsive phase. Once again, orienting the body in a horizontal position is a must, as this provides streamline for the swimmer as their arms gain propulsion. The kick during the entry counteracts the vertical forces which act upon the arms. 

Second Kick

The second kick happens as the hands finish the catch phase. This kick maintains an elevated hip position. This kicks helps keep the hips high, the body in a relative streamline, as the chest and head rose for a breath.


Many perform large kicks during the butterfly, but this is likely unnecessary, bringing the body out of streamline. Although it may help some swimmers time their streamline during propulsion of the catch, it is still wasteful and beneficial if eliminated. Remember, small, fast kicks which counterbalance the arms and streamline the body optimize butterfly horizontal velocity.

Written by G. John Mullen who received his Doctorate in Physical at University of Southern California (USC) and is a certified strength and conditioning specialist (CSCS). At USC, he was a clinical research assistant performing research on adolescent diabetes, lung adaptations to swimming, and swimming biomechanics. G. John has been featured in Swimming World Magazine, Swimmer Magazine, and the International Society of Swim Coaches Journal. He is currently the owner of COR, providing Physical Therapy, Personal Training, and Swim Lessons to swimmers and athletes of all skills and ages. He is also the creator of the Swimmer’s Shoulder SystemSwimming ScienceSwimming Science Research ReviewMobility System and the Swimming Troubleshooting System.
Dr. John Mullen, DPT, CSCS world-renowned physical therapist and strength coach.
  1. May 9, 2016

    Morning John,

    Lots of contradictions in this article:

    The highlight box says the first kick occurs at the arm entry but the body of the article says it should be just before the hand entry. The ‘at’ or ‘just before’ are obviously incompatible. I would suggest that both are not only incompatible but also somewhat misleading.

    The highlight box says the second kick occurs at the arm exit but the body of the article says it occurs as the hands finish the catch phase. ‘[A]t the arm exit’ and ‘as the hands finish the catch’ are apparently contradictory but you do not define the start and finish limits of the ‘catch phase’. I would suggest that both are not only contradictory but also wrong.
    Incidentally the embedded link to the How to Swim the Butterfly article results in a 404 and searching on the site produces no result for me.

    Let me explain my observations and understanding of butterfly.

    Way back in 1967 The Science of Swimming described the ‘keyhole’ shape of butterfly arm pulls when viewed from underneath the swimmer. Nowadays that keyhole shape has narrowed dramatically as the fastest swimmers have focused on strength gains and been able to move more and more towards a straight line pull which directs the water backwards rather than diagonally out, in and back. However, human anatomy still compels the hands to describe a shape akin to a keyhole, albeit a thin one.

    In 1975 Howard Firby (Howard Firby on Swimming) described butterfly as simply the two longitudinal halves of freestyle performed simultaneously and symmetrically. It’s a beautifully insightful observation.

    Then in 1982 Dr. Maglischo’s first epic, Swimming Faster’ described how the kick rhythms of freestyle, backstroke and butterfly coincided with the underwater sweeps of the arm actions. That coordination between the leg movements and the arm movements is not only important but it is a fundamental key to effective swimming. Human anatomy and the associated biomechanics demand that the coordination occurs in precisely this manner. If it does not then the swimmer creates the circumstances of their own demise.

    Maglischo’s description of the butterfly arms outsweep, insweep and upsweep gives us the start and finish points for the movements encompassing what you describe as catch and exit. The outsweep starts at the hand entry and finishes when the hand changes from outsweep to insweep as part of the famous keyhole pattern and that is where the ‘catch’ occurs – at the point of change of direction. The insweep starts at that point of direction change and it ends when the hand changes direction again after coming close together or even overlapping under the stomach of the swimmer. The upsweep starts at that second change point and ends as the hands release the water pressure in preparation for the exit.

    We have therefore four ‘check marks’ – 1) entry, 2) catch, 3) change from pull to push under the stomach, and 4) release/exit. The overwater recovery takes the swimmer around the stroke cycle merry-go-round again, moving from #4 back to #1. Rinse and repeat.

    Effective butterfly kick is more sophisticated than a simple up and down action: depending on the swimmer’s hip, knee and ankle flexibility it describes a heart-shaped pattern when viewed from behind. This allows the swimmer to apply more pressure with the instep and apply it for a longer distance. However for the purposes of this analysis the simple up and down directions will suffice.

    Up and down are two distinct movement directions. Most butterfly exponents use a two-beat style (yes, there are examples of one-beat fly swimmers – Summer Sanders for example – but most use two-beat). Two kicks each with two directions produces four movements – down, up, down, up. The start and finish of those four leg movements MUST coincide with the four arm check points for the butterfly technique to be effective. The downbeat of the first kick must start at point #1 (hand entry) and must finish at point #2 (catch). The upbeat of the first kick must start at the catch (2) and must finish at the next point of transition (3). The downbeat of the second kick must start at that transition (3) and must finish at the release (4). The upbeat of the second kick must start at the release (4) and must finish at the next hand entry (1).

    It is so simple and elegant that when it is performed correctly butterfly becomes a thing of incredible beauty; the swimmer slices through the water like a hot knife through butter and then flies across the surface.

    When the timing is ‘out’, when the phases of the kicks do not coincide precisely with the phases of the arms, then the stroke efficiency deteriorates – butterfly becomes butter-cry and eventually butter-die.

    Swimmers who use a one-beat style simply omit one of the two recommended leg kicks. They don’t change the timing of the kick that they do use; they simply omit the other kick. Summer Sanders used a strong ‘first’ kick and trailed her legs during the period reserved for the ‘second’ kick.

    The timings of the up and down movements for the long-axis strokes, freestyle and backstroke, are exactly the same except that they are performed alternately (backstroke is upside-down, so up becomes down becomes up and up becomes down). The check-points 1-2-3 occur for each arm so we end up with a total of 6; hence a 6-beat kick is the preferred norm. Swimmers who use a 2-beat kick or 2-beat crossover simply omit the other kicks; they do not change the timing of the kicks they do use. 4-beat kickers do not perform 2 beats on each side, instead they perform three movements on one side (in effect half of a 6-beat rhythm) and one on the other side (half of a 2-beat rhythm). Anything else would result in very ugly swimming and ugly swimming is slow swimming.

    The summary of the article says ‘large kicks are unnecessary. Well large or small depends on the pattern of the arms phases. Swimmers with a very long upsweep towards the release/exit (think the GOAT) will have a relatively large/long second kick downbeat during that phase because it MUST coincide. Swimmers with a very short outsweep will have a relatively short/fast first kick downbeat.

    The article summary cracks it with its conclusion: “small, fast kicks which counterbalance the arms”. Exactly. The kicks must counterbalance the three underwater phases of the arms. If they do that then the swimmer will be both effective and efficient.

    Regarding breathing: when describing the second kick the article says, “The second kick happens as the hands finish the catch phase. … as the chest and head rose (sic) for a breath.”

    That is not the point where the best butterfly swimmers take their breath; in fact that’s where novice butterfly swimmers start to flounder. The second half of the upsweep (check-mark 3 to check-mark 4) forces the head and chest forward. Elongating the neck during that phase to make the chin reach forward (not upwards) allows an in-breath to be taken with the least disruption to streamlining. The ubiquitous side-on photos of Michael Phelps breathing as his hands start to exit aptly illustrate this. The rule seems to be the later the breath is taken during the propulsive phase of the arm stroke the better.

    Because the right and left side arm and leg movements of butterfly are simultaneous and symmetrical they provide the simplest example for our understanding of the required timing and coordination for both front crawl and backstroke. All three strokes follow exactly the same principles. If they do not they become ugly and slow. Breaststroke, of course, is a different kettle of fish altogether!

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