Both legs are kept parallel, fairly straight, and quickly flutter up and down with toes pointed.
This article explains the technique of the flutter kick as it is used in the front crawl stroke.
We also discuss the following topics:
- Kicking rhythms.
- The amount of propulsion generated by the legs.
- The stabilizing role of the kick.
- Common mistakes.
- A few additional tips to improve your technique.
Let us now go into more detail about the technique of the flutter kick. Here’s a short video demonstrating the flutter kick:
The legs are always kept parallel and move in opposite directions. As one leg moves downward, the other one moves upward and vice versa.
In the first half of the downbeat, the downward movement is initiated by a slight flexion of the leg at the hip.
Shortly after that, the knee also bends a little. The foot goes into plantar flexion (meaning the toes are pointed, both by muscle contraction and by the pressure of the water against the foot as it moves downwards.
During this phase, the upper side of the foot is facing downwards and a little backward. For this reason, while the foot is moving downwards, some water is pushed back. This is how propulsion is created in the flutter kick.
In the second half of the downbeat, the hip is locked in place while the knee stretches. The toes are still pointed. This phase isn’t propulsive but prepares the leg for its upward movement.
The upward movement of the leg begins while the knee is still stretching. As the thigh moves upwards, the pressure of the water against the lower leg causes the leg to straighten.
The pressure of the water on the ball of the foot and on the toes brings the foot to a neutral intermediate position. This phase of the flutter kick is not propulsive either.
The two most common front crawl kicking rhythms are the two-beat kick and the six-beat kick. There are also less common four-beat kick variations, but they will not be discussed here.
In the two-beat kick, you kick once per stroke cycle with each leg. The downbeat of the right leg occurs during the propulsive phase of the right arm stroke (during the insweep and upsweep phases, to be more precise).
Total Immersion coach Matt Hudson using a two-beat kick
Lots of middle- and long-distance swimmers use the two-beat rhythm because it uses less energy than the six-beat kick.
It is also quite popular among swimmers who have been trained in the Total Immersion method.
In the six-beat kick, each leg kicks three times per stroke cycle, for a total of six kicks for both legs.
For example, if we concentrate only on the movements of the right arm and leg, the timing of these kicks is as follows:
1) The first downbeat of the leg occurs while the arm extends forward underwater.
2) The second downbeat of the leg takes place during the upsweep of the arm.
3) The third downbeat of the leg occurs during the arm recovery.
The same timing can be observed between the left arm and leg.
Ian Thorpe using a six-beat kick during his 400 m freestyle world record swim at the 2002 Commonwealth Games.
The six-beat kick is almost always used by short-distance swimmers, but can also be observed at times with medium-distance swimmers and long-distance swimmers—with a somewhat subdued kick.
Contribution of the Flutter Kick to Propulsion
The primary role of the legs in the front crawl is to generate propulsion. Indeed, it is common knowledge that world-class swimmers have a powerful kick (often made possible by large feet).
From this, we can conclude that a strong flutter kick is an essential prerequisite for fast swimming, but how much do the legs contribute to the overall propulsion?
It’s less than generally thought. Studies have shown that in elite swimmers, the legs only contribute about 10% of the propulsion. The lion’s share of the propulsion is generated by the arms, at least in the front crawl.
Stabilization of Body by the Kick
The secondary role of the flutter kick is to stabilize the body.
This is because the movements of the arms and legs compensate each other so that the body does not roll sideways.
The beginning of the propulsive phase of the arm stroke on one side always coincides with a downward movement of the leg on the same side, preventing the body from rolling.
There are some common mistakes in the flutter kick that affect its efficiency and should, therefore, be avoided:
Using a Large Kick
A large kick requires more power and also increases drag and therefore, should be avoided.
To bring drag to a minimum, the kick should remain in the shadow of the body moving forward. Ideally, the kick should break through the surface of the water only slightly, and should not move below the line of the body.
The best way to describe the flutter kick is to make fast, compact upward and downward movements that are initiated by the hip.
Using a Bicycle Kick
If you bend your knees too much while flutter kicking, it will look as if you were riding a bike.
The problem with this is that the back of your lower leg moves forward and not upward. The water is then pushed forward, slowing you down.
Instead, the kick should be initiated by slightly bending the hip during the downbeat. The knee will then follow accordingly, but you must only bend it slightly.
Using Too Much Power During the Upbeat
In the front crawl stroke, the upbeat phase of the kick isn’t propulsive. Therefore, you should only use just enough energy during the upbeat to move your leg upwards, but not more.
Bending Your Knees and Pointing Your Toes during the Upbeat
These two mistakes are closely related to the previous one.
If you put too much force into the kick during the upbeat, you’ll also be prone to bend your knees and point your toes, which wastes energy and increases drag.
If you relax your legs during the upbeat, the water pressure will straighten them without you having to drive the movement.
1) If you have stiff ankles, as is often the case with runners, it can be difficult for you to point your feet back. Your feet will probably be pointing down and maybe even a little forward.
If this is the case, your kick may not provide much propulsion or no propulsion at all. To correct this, you can use swimming fins and stretch your ankles regularly to improve their flexibility.
2) If you want to learn the flutter kick on its own as a prerequisite for learning the front crawl, the following article proposes a set of drills to learn the flutter kick in a prone position (i.e., floating face down).
You may also be interested in the following articles that cover the front crawl’s swimming technique: