2-Beat Kick Purpose

Here are my comments in response to a swimmer’s question about when to use the 4-Beat Kick and/or 6-Beat Kick:

The point of the 2-Beat Kick is that it brings the entire body together in ONE synchronized rotation movement. The kick in 2BK is intended to assist rotational force, which the body then converts into forward force through a corkscrew-like effect which uses the body’s built-in rotational force-generating mechanics (see Myofascia And Swimming). This rotational force is channeled to the cutting edge of the body in a careful shaped and timed stroke.  The 2BK is not intended to directly generate forward force as the 4Bk and 6Bk are – these require a significant amount of disconnect between the lower body and the upper body at the waist so that the hips can respond to the kick pattern while the shoulders respond to the arm-stroke pattern which are on different rhythms.

The 2BK has a completely different purpose than the 4BK/6BK, and because of this makes no sense as a direct forward propelling effort. When a swimmer switches to a 4BK or 6BK she is not merely changing the rhythm, she is also changing the way force is applied and transferred through the body. 4BK/6BK are not the same kick simply applied at a higher tempo.

The conflict between 4BK/6BK and full body synchronization is that each back-press of the foot then works against the effortless balance of the body – for every action there is an opposite reaction. The second or third back-press of the foot at different moments during the body rotation create counter-force to the rotation. These back-presses out of sync with where the upper body is going will work against rotational flow in that moment when the body should be finishing its rotation undisturbed by such counter-forces. This means the swimmer must produce counter-forces within her own body to preserve balance – an obvious point of energy waste. So implementing a 4BK/6BK requires a thoughtful trade-off – they change the manner and amount of force generated, at the cost of breaking the lower-drag, higher energy savings advantage of the full-body sync. 4BK and 6Bk are tools to be kept (and trained for) in the competitive swimmer’s toolbox, but they must also be applied with intelligent consideration as to what the swimmer is trying to gain and at what cost in energy.


If you would like to test this yourself here is an experiment you can do:

  • Head for deeper water – over 2m – so you can position yourself vertically without touching the bottom.
  • If you have them, wear short fins (I highly recommend the Finis Positve Drive because of their high responsiveness).
  • Hug yourself, with hands on opposite shoulders.
  • Hold your breath for a little while during the exercise.

Now we’ll experiment with different kick patterns and examine how the forces affect the body position…

Do a flutter kick to push your head above the surface and hold it there for a few seconds. This kind of kick is what may most readily be recognized as a 6Bk (if you put the arm stroke on top of it).

Without having to concentrate on exactly what the feet are doing, you are shaping the kick in such a way to apply force directly downward in order to push the body directly upward against gravity. This reveals the direct-forward force generation of a 4BK and 6BK. This is what they are meant for.

You can use this position to alter and test where the kick is being powered from – keep the legs fairly straight with the slightest flex at the knees (think strong but flexible tree branch) and you’ll move the power generation to the upper legs, buttocks and hips. Let the knees bend more and you’ll move the work to the thighs and hamstrings. (Notice how the amplitude of the kick changes as you change the kick style.)

Observation 1:  In this kick pattern the body can stay vertical relatively easy – the two feet pressing in opposite directions balance each other and resist the body twisting and resist the body leaning forward or backward. Kicking this way translates into a swimming position that prefers a flatter body position – fast tempo kickers will usually permit far less rotation than slow tempo ones.

Now, turn off the power of the back-press (the forward foot pressing backward). In order to do this you will be forced to turn off the scissors-like motion, and keep just the forward-press of each rear foot. At first, the non-working foot may be confused about what it should be doing. Just let it swing in counter-balance, but not counter-force.

Observation 2: This will immediately translate force through the body differently – if you disconnect your lower body from the upper body at the waist you can prevent the upper body from rotating. If you keep the hips/shoulders/head as a solid unit you’ll notice the upper body wants to rotate on each forward press of the foot. The press of the foot initiates the rotation of the upper body in the opposite rotational direction, with the pivot point about the spine.

Now, intentionally change how you use the force of that kick – rather than try to push your head above the surface, use the press of the left foot to turn your torso (hips/shoulders/head as one solid unit) 1/4 turn to the left, and use the press of the right foot to rotate the torso back to the right. Because you are applying force to enable rotation rather than upward motion, your body sinks down in the water to a balance point with gravity. You are now directing force differently, for a different purpose.

Observations 3: You will also notice, in this rotational kick pattern, that the body wants to angle forward, as if falling forward onto your face. When just one of the feet are applying force in only one direction (forward in vertical position, downward in prone position) then physics requires a counter force to keep the body vertically stable – if there is none the kick force will find a pivot point somewhere above your navel then push your upper body forward in reaction. A well-timed 2BK generates two benefits – it supports the whole body rotation, and it drives the lower body up and the upper body down. It is an affect that resembles something known as precession in physics, (but the human body is hardly a gyroscope).

I recommend this vertical self-hug kick position to test the affect of these various kicks because it is so much easier to observe these physics laws at work in vertical position than horizontal, but the same are working in both positions. We just don’t notice it as easily in horizontal swimming because many other things capture the swimmer’s attention in that position.


At the beginning of learning a 2BK, most humans tend to move their legs in a scissor-like counter-force way – one leg/foot pressing backward and one leg/foot pressing forward. This may likely be attributed to our land-mammal instinct. This is what holds the body steady against the alternating asymmetrical kicking force. This may be the way to make a nice 4BK/6BK but this is not the way to make a nice 2BK. However, you may likely need to begin working on the 2BK connection with such a scissors-like kick at first – getting the rhythm is the most important first step. You’ll just need to learn to stop the scissors in the next step of your refinement.

Ultimately, you will want a 2BK that has only the back foot applying a down-ward pressure, while the other foot is holding its place in a long-body line. As the left back foot presses, the body will rotate onto right-side streamline. The right leg will gently swing back nearly into position to press at the appointed moment, to assist the body rotating onto left-side streamline. At the appointed time, there is a slight drop in the knee and a slight lift of the heel – all keeping within the envelope of the body – then ‘flick’ at the precise moment to finish the body rotation.

There is no scissors, counter-force kick happening. Only one foot is pressing, while the other is ‘resting’ so-to-speak. They take turns – one pressing, while the other holds the streamline.

You can see clearly in my demo video here how one leg presses, while the other holds the long body-line. There is no scissor motion. You can also see how I can leverage the kick at the hip (it makes me think of flicking a fly line from the end of a fly-fishing rod) and drop the knee just a tad to provide flex, while keeping it all hidden behind the body – the thighs nor knee drop below my lowest body line, and the heel, ideally, does not catch any air at the surface. (Remember: bubble = vortex = low pressure zone = no traction = wasted energy).

sun yang kick

You can also see this 2BK ‘one-leg pressing’ idea in this slow-motion video of Sun Yang, though his kick is not so clean or consistent in every stroke. With my eyes I see its value for rotational thrust, but don’t perceive that it carries value for direct-forward thrust (I can only speculate). The residual 4BK reflex we see there may be an unintentional one. We might forgive him these flaws. Even swim-gods have things to clean up and at highest intensity swimming all our default modes and details will be revealed, just like Sun Yang’s are despite his WR performance. He’s the fastest human at 1500, but still, at best, someone like him is estimated to be only 7% efficient with his power as compared to dolphins who get up to 80%.

The higher we try to go, performance – or lack thereof – is affected by the accumulation of a hundred small details in favor or against that performance. Every minute detail has a energy cost saving or expense attached to it. As a discipline, learn to track and improve those details carefully in the early stages of your learning and performance and it will turn into a massive advantage near the top.


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3 responses to “2-Beat Kick Purpose

  1. This is an excellent article of 2BK. It provides a detailed explanation and ways to experiment. The functions of 2BK distinguishing from 4BK/6BK are clearly explained.

  2. Excellent article, particularly the point about both the form and coordination required to incorporate into your stroke form without losing overall efficiency. My 17 Y/O son’s coach has him working on incorporating a 6BK into his 500/1000/1650s with a goal of making super sectional cuts (ie holding a sub 60 sec/hundred yard pace) and my son is quick to note the difficulty in maintaining hip rotation and timing for extended distances with such a fast kick (thus the “disconnected” feeling).

    • This understandably puts the coach in an awkward position. He can’t possible teach something he may not know much about, and not want to take the risk to follow that 2bk approach with his swimmers especially when they start getting into the zone of being successful in races. The 2bk is not used so much, not examined and its function and formation not well understood.

      And this is a challenge for the parent and the swimmer, when they see some aspect of technique they believe in and are willing to pursue yet their coach is not in position to support it with training know-how. He may be encouraging but it can easily make a coach feel insecure or inadequate when they think they cannot satisfy every need of their swimmers.

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