Increase the Speed of Your Freestyle and Dolphin Kick

How to Increase the Speed of Your Freestyle & Dolphin Kick

Part I: Getting the Motion Right

The amount of propulsion generated by the kick is arguably the most important difference among fast and not-so-fast swimmers. While the motions involved in the propulsion for freestyle, butterfly and backstroke kicks are similar, the breaststroke kick requires an entirely different set of physical attributes. For now, we will focus on freestyle or flutter kick.

As with the pull, the propulsion generated by the kick depends on the amount of surface area of the foot and the speed of that surface pushing backward (relative to the water). Unlike the pull, where the water in front of the hand moving backward is relatively still, the flow dynamics behind the swimmer (vortices) contribute significantly to the amount of propulsion generated by the foot.

There are three articulations involved in the freestyle kick; the hip, the knee and the ankle. To kick fast, they all need to be just right. As with the pulling motion, the ideal kicking motion must reach a compromise between the propulsive forces and the frontal drag forces.

The saying ‘bend but don’t break’ could not apply more appropriately than with the kicking motion. Having plantar flexibility of the ankle is the single most important physical attribute of a fast kicker. With greater plantar flexibility of the ankle, less knee bend is required to get the same amount of surface area of the top of the foot pushing backward. Some knee bend is required in all fast freestyle kicking, but once the bend of the knee passes around 60 degrees, the system breaks down. The drag coefficient increases dramatically and the swimmer decelerates quickly. A strong kicker with plantar flexibility knows exactly how much to bend the knee on each kick, before snapping the foot backward. A poor kicker with little plantar flexibility will often bend the knee well past 60 degrees in order to get more foot surface area to push backward. In so doing, he nearly comes to a screeching halt. The increase in propulsion he may get from over bending the knee will not offset the deceleration caused by the frontal drag from the knee bend. The resulting inefficient, varying speed does not conform to the law of inertia.

In order to reach the optimal knee bend for maximal kicking speed in freestyle and dolphin, the foot must come out of the water during the up kick. Swimmers with poor plantar flexibility tend to bring the foot too far out of the water. With great freestyle kickers at maximum effort, one sees a virtual boil of water formed behind the swimmer from the continuous hard motion of the foot in both directions. For more on the dynamics of the kick and vortices the foot can create read this Aqua Note.

Yours in Swimming,

Gary Sr.

Read Part II: Kick Faster in Freestyle and Dolphin Kick

Read Part III: Two Important Nuances of a Great Kicker

Read Part IV: Five Ways to Kick Faster in the Pool

16 Responses to Increase the Speed of Your Freestyle and Dolphin Kick

  1. Stanley

    Hi Gary,

    When you say “the foot must come out of the water during the upkick” for an optimal knee-bend, for flutter kick and dolphin, does this mean the entire foot of each leg, or the heel of each foot? Wouldn’t this be kicking air? I know the kick has to be close to the surface, and I notice that when some fast swimmers are very high on the water, their feet tend to come out of the water though not drastically (Ledecky, for instance).

    Thank you.

    Stanley

     
    • garyhallsr

      The entire foot does not typically come completely out of the water, but it is close. the faster one kicks, the more of the foot comes out. Even though it would seem putting the foot in the air would reduce propulsion, the bend of the knee that causes that to happen seems to outweigh the air with respect to increasing propulsion. Kicking underwater is faster, whether freestyle or dolphin, because the foot remains in the water and surface drag is eliminated.

       
  2. Stanley

    Hi Gary,

    Thank you for the clarification! If a very fast middle distance swimmer is bringing one foot out of the water so that it is almost or completely out of the water, and that swimmer is maintaining a constant rotary pull/push arm stroke, would the water resistance of the swimmer be reduced for the fraction of a second when the foot is out of the water? That might account for the non-reduction of speed when the foot is out of the water for very fast swimmers (I was
    thinking of Ledecky. When she speeds up, her feet come out of the water. Maybe that makes her faster by reducing wind resistance. Or maybe not).

    Best regards,

    Stanley

     
  3. Stanley

    Hi Gary,

    Sorry, that’s reducing water resistance. “wind” is an error.

    Best regards,

    Stanley

     
    • garyhallsr

      With only two hands, there can never be constant propulsion from the pull. In other words, there is always some ‘down time’ when neither hand is pushing backward. The three most important factors that cause deceleration from the kicking motion are the degree of knee bend, the speed of drawing the foot up past horizontal on the up kick and the degree the the foot hangs down after the down kick. With the kick there is propulsion from both the up and down kicks and both are going on at the same time (in freestyle), so there is less change of speed than with the pulling motion, conforming more to the law of inertia.

       
    • garyhallsr

      BTW, for all swimmers there is a threshold speed where the kicking motion will actually slow the swimmer down more than add propulsion. That speed will depend on the drag caused by the kicking motion. For most good kickers, that speed is faster than they will normally swim.

       
  4. garyhallsr

    With only two hands, there can never be constant propulsion from the pull. In other words, there is always some ‘down time’ when neither hand is pushing backward. The three most important factors that cause deceleration from the kicking motion are the degree of knee bend, the speed of drawing the foot up past horizontal on the up kick and the degree the the foot hangs down after the down kick. With the kick there is propulsion from both the up and down kicks and both are going on at the same time (in freestyle), so there is less change of speed than with the pulling motion, conforming more to the law of inertia.

     
  5. Oliver K

    Dear Gary,

    it would be great if you could also think about the adult late starters for this topic — it is SO HARD to get any information here!

    Kicking really fast is still a big mystery for me. I am 51, swimming seriously for a couple of years now. The best I can do over 25m is 23 sec (with the Finis snorkel, arms in streamline position), which seems good for my peer group, but of course very bad from an absolute point of view.

    A month ago, via a video analysis it was realised that I had a very large kick. That was actually my way of getting some speed :-( Now there wasn’t much knee bend in the kick, it is just a very big kick. I kind of developed this over the last half a year or so, in my attempts to get a better kick. Namely I realised that for the vertical kick, the big kick does a good job, and then I transferred that to the whole stroke. So well, now for one month I concentrate to get the kick small. I realised that very different muscles are involved. Especially it seems that for the snapping action I don’t have the muscles yet! Pure kicking is not faster yet, but the whole stroke feels much easier, relieved, now — it rocked the whole boat, that large kick (with rather straight legs).

    It would be really great to get some precise information (numbers would be great!!!!!). Also a video, showing the (pure) kick with speed information, under water, would be very very informative. You have a video showing how somebody does 25m in around 15sec, but there’s nothing to see (as far as I can tell), and I have no clue what it would look like under water. Frequency information would also be great. Perhaps the experienced swimmer/coach can tell, but for me it is basically impossible to guess from a slow motion anything about speed and frequency. (Actually, if not for a dedicated comment, slow motion these days seems a bad idea to me, since, at least when downloading the video, everybody can do this himself, having the original, while have only the slow motion the original is just lost, and one doesn’t know whether this is just training, exaggeration, or real swimming.)

     
    • Oliver K

      Just to clarify: with the “vertical kick” I meant the vertical kicking exercise, where with a big kick I managed well to get the head high out of the water, with the elbows at the surface. The small kick here seems much more strenuous, and I thought “so well, swimming is not a beauty contest, so why not going for what is more efficient”. Very different core muscles seem involved here for the large kick versus the small kick. So that having a “strong core” didn’t really help here, but the point is having the “right core”, so to speak. Meanwhile, after a month, I see the light again with vertical kicking (so to speak ;-)). Still, doing the vertical kicking right at the wall, with really very small leg movements (to avoid hurting your knees), I can hardly keep my head above water, but that seems anyway not so easy (without fins).

       
      • garyhallsr

        The difference between vertical kicking and horizontal kicking is that there is no forward motion with the vertical kick, so frontal drag does not come into play. By separating your feet widely and not bending the knee you must be flexing/extending more at the hip….which also leads to more frontal drag. Over time, you will need to develop more plantar flexibility of the ankle so you don’t over bend either knee nor hip to generate propulsion.

         
      • garyhallsr

        The best way we have to show the effects of the motions of the kick and pull is by using velocity meter (Speed RT) which shows velocity, acceleration and deceleration at intervals of .04 seconds during the kick or pull. From this, one can begin to appreciate the sensitivity in water to small positional changes. We will be showing more of this in our Swimisode series starting this summer.

         
  6. Sang Hwa Lee

    How to Increase the Speed of Your Freestyle & Dolphin Kick
    팔랑 차기와 돌고래 차기 속도를 늘리는 방법

    Part I: Getting the Motion Right
    1부 : 움직임을 올바르게 하기

    The amount of propulsion generated by the kick is arguably the most important difference among fast and not-so-fast swimmers. While the motions involved in the propulsion for freestyle, butterfly and backstroke kicks are similar, the breaststroke kick requires an entirely different set of physical attributes.
    차기에 의해 생성된 추진력의 양은 틀림없이 빠른 수영 선수와 그렇지 않은 선수의 가장 중요한 차이입니다. 자유형, 접영 및 배영 차기의 추진력과 연관된 움직임이 유사하지만, 평영 차기에서는 완전히 다른 신체 움직임 특성을 요구합니다. 이번에는 자유형 차기 즉 팔랑 차기에 집중하겠습니다.

    As with the pull, the propulsion generated by the kick depends on the amount of surface area of the foot and the speed of that surface pushing backward (relative to the water). Unlike the pull, where the water in front of the hand moving backward is relatively still, the flow dynamics behind the swimmer (vortices) contribute significantly to the amount of propulsion generated by the foot.
    팔 젓기와 마찬가지로, 차기에 의해 생성되는 추진력은 발 표면적의 넓이와 그 표면적을 (물에 대하여 상대적으로) 뒤로 미는 속도에 달려있습니다. 손에 의해 뒤로 움직여지는 물이 비교적 정지해있는 팔 젓기와는 달리, 선수의 뒤에 생기는 유체 역학 현상(소용돌이, 와류)이 발에 의해 생성되는 추진력의 양에 상당한 이바지를 합니다.
    There are three articulations involved in the freestyle kick; the hip, the knee and the ankle. To kick fast, they all need to be just right. As with the pulling motion, the ideal kicking motion must reach a compromise between the propulsive forces and the frontal drag forces.
    자유형 차기에는 3개의 관절이 관여합니다; 엉덩관절, 무릎관절 그리고 발목관절. 빠르게 차기 위해서는, 이 세 관절이 모두 올바르게 움직여야 합니다. 팔 젓기 동작과 마찬가지로, 이상적인 차기 동작은 추진력과 전방 저항력 사이에서 절충을 이루어야 합니다.
    The saying ‘bend but don’t break’ could not apply more appropriately than with the kicking motion. Having plantar flexibility of the ankle is the single most important physical attribute of a fast kicker. With greater plantar flexibility of the ankle, less knee bend is required to get the same amount of surface area of the top of the foot pushing backward. Some knee bend is required in all fast freestyle kicking, but once the bend of the knee passes around 60 degrees, the system breaks down. The drag coefficient increases dramatically and the swimmer decelerates quickly. A strong kicker with plantar flexibility knows exactly how much to bend the knee on each kick, before snapping the foot backward. A poor kicker with little plantar flexibility will often bend the knee well past 60 degrees in order to get more foot surface area to push backward. In so doing, he nearly comes to a screeching halt. The increase in propulsion he may get from over bending the knee will not offset the deceleration caused by the frontal drag from the knee bend. The resulting inefficient, varying speed does not conform to the law of inertia.
    ‘굽히세요 하지만 꺾지는 마세요’는 차는 움직임에 가장 적합하게 적용되는 말입니다. 발목이 발바닥 쪽으로 잘 굽혀지는 유연성은 빨리 차는 선수의 가장 중요한 신체적 특성입니다. 발목이 발바닥 쪽으로 잘 굽혀질수록, 무릎을 덜 굽혀도, 물을 뒤로 밀어내는 발 모양의 표면적 크기를 동일하게 할 수 있습니다. 빠른 자유형 차기를 하려면 언제나 무릎을 조금 굽혀야 하지만, 무릎을 굽힌 각이 60도를 넘게 되면, 체계가 무너집니다. 저항계수가 극적으로 증가하여 선수는 금방 느려집니다. 발바닥 유연성이 좋아 강력하게 차는 선수는 매번 찰 때마다 발을 뒤로 채기 전에 어느 정도까지 구부려야 할지 정확히 압니다. 발바닥 유연성이 좋지 않아 서투르게 차는 사람은 뒤로 미는 발 표면적을 더 크게 하려고 종종 60도가 넘도록 무릎을 굽히기도 합니다. 그렇게 하다가, 거의 끼~익 소리 나도록 브레이크가 걸리기도 합니다. 무릎을 과도하게 굽힘으로써 증가한 추진력이 그렇게 무릎 굽힘에 의한 전방 저항이 초래하는 감속을 벌충하지는 못합니다. 그 결과로 생기는 비효율적인 속도 변화는 관성의 법칙을 잘 따르지 않게 됩니다.
    In order to reach the optimal knee bend for maximal kicking speed in freestyle and dolphin, the foot must come out of the water during the up kick. Swimmers with poor plantar flexibility tend to bring the foot too far out of the water. With great freestyle kickers at maximum effort, one sees a virtual boil of water formed behind the swimmer from the continuous hard motion of the foot in both directions. For more on the dynamics of the kick and vortices the foot can create read this Aqua Note.
    돌고래 차기와 팔랑 차기에서 최고 속도를 얻기 위한 최적의 무릎 굽힘 각도에 도달하기 위해서는, 위로 찰 때 발이 물 밖으로 나와야 합니다. 발바닥 유연성이 좋지 않은 선수들은 발을 물 밖으로 너무 높이 내놓는 경향이 있습니다. 자유형 차기를 아주 잘하는 사람이 최대한 가장 빨리 찰 때는, 끊기지 않고 아래위로 차는 발의 맹렬한 움직임 때문에 선수 뒤로 마치 물이 끓는 것 같은 흔적을 보게 됩니다. 차는 것의 동역학과 와류(회오리)에 대해 더 알고 싶으시다면, 이 Aqua Note를 참고하세요.

    Yours in Swimming,
    당신의 수영과 함께 하는,

    Gary Sr.
    게리 홀 시니어.

     
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