A flutter kick – sometimes called a 6-Beat or a 4-Beat kick, when it’s done correctly – is useful for some people in some circumstances, but certainly not for all, and I would like to argue that it may not be best for most. However, it is certainly necessary if the swimmer does not have a balanced body and must struggle to keep the legs from sinking. But once this is solved, the question remains whether a constant flutter to push forward is helpful and worth the cost or not.
In order for a flutter kick to actually assist in forward movement at a reasonable energy cost, the ankles need to be very flexible, and having larger feet helps (= more surface area to press against the water). There are different ways to form the kick and the way in which it is done is important because when not done skillfully, the bending of the legs at the hips and knees produces excessive drag which negates a great portion of the thrust the swimmer tried to create from that kick. The net result is a kicking action that uses an enormous amount of energy for very little or no benefit to forward motion. In addition, the fluttering legs require the hips to pivot with them, while the torso is rotating on a different (slower) rhythm. This requires the hips to disconnect from the upper body, creating a twisting motion between the vertebrae of the lower lumbar spine. For those with lower back vulnerabilities, twisting at the lower spine is not going to be pleasant. This may seriously increase the risk of lower back pain (and young people fluttering along might not have their spine worn down enough to feel it yet).
Instead, we promote a 2-Beat Kick where the legs and hips are tied into the torso and move in the same rhythm. The whole body is one unified propulsive unit, using rotational thrust. This eliminates the twisting between vertebrae in the lower back. Rather than being used to push back on the water, the 2-Beat kick motion is used exclusively to enhance torso rotation. Try it with a kick board and you’ll see that it doesn’t really push you ahead. But, when done well, its very good for helping rotate the torso.
You can see a demonstration of the 2-Beat Kick in these videos below, at fairly brisk tempos…
The decision to use a flutter kick or a 2-Beat Kick is a matter of trade-offs. In the flutter kick the legs are disconnected from the torso in order to produce linear (rearward) thrust that is combined with the pulling action of the arms. But those are two separate actions in separated sections of the body. The body is divided at the waist so that the lower part can move in a way that serves the kick and the upper part can move in a way that serves the arm strokes. And, even for those with suitable foot form and good kick technique, it takes a lot of energy for a modest increase in thrust. It may be worth the expense for short distance pool swimmers, and it might be tactical to use it at the very last meters of a longer race (as Sun Yang did to set the world record in the 1500), but it is a questionable expense for long distance swimmers, especially those who are not set up with a body for kicking.
I imagine that most people without extremely flexible ankles and without good kick technique are pushing down on the water much more than pushing back anyway. They are fluttering the feet in a rhythm that does not allow that downward press of the foot to connect with the timing of the torso rotation. The legs might be lifted higher in the water by the fluttering, but that’s about it – the kick does not provide useful linear thrust and it does not assist rotational thrust. It is simply an energy-expensive way to keep the legs from sinking. So we urge the obvious solution: learn to balance the body which removes or greatly reduces sinking, and one no longer needs to hold the legs up with a flutter kick. Which means the legs can be put to work in another way.
If I had bigger feet and the ankle flexibility to flutter kick effectively, I’d probably use it more often on my sprint work (and my ankles are surprisingly flexible for a runner). But for distances beyond sprinting (anything over 400 perhaps) there is no question – the 2-Beat Kick is a much better trade off for most of the swimmers I see. But we have to work on it to get that benefit – there are different ways to do the 2BK and it matters how its done.
This is one of my main arguments for encouraging swimmers to adopt the 2-Beat Kick over the flutter kick, for most of their swimming needs. Meanwhile, if one has the feet and ankles and technique to do it well, the flutter kick can still be useful and applied for sprints, and enjoyed if it feels good (if you like kicking along with a board, talking to a friend, for example). Of course, if you plan to use the flutter kick occasionally, you still need to practice it so that those particular muscles get fit for action – it doesn’t come easy for most people and it always costs a decent amount of energy.
PS: I’m not against flutter kicking – just that its used appropriately and done well, and I would like to relieve people who just don’t have the feet to make it happen no matter how much they are made to do laps with a kick board. I’d actually love to see an event added in competitive swimming that is just pure kicking, no arms!
You may view this entire series:
- Your Kick And Lower Back Pain
- Why Choose A 2-Beat Kick?
- Learning The 2-Beat Kick – Part 1
- Learning The 2-Beat Kick – Part 2
And, if you like this topic, you may view some posts I’ve written on this in the past:
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