This article describes the technique of the flutter kick in the front crawl stroke. It also covers common mistakes, kicking rhythms and some tips to improve your technique.
To get started, let's have a look at a video that shows the freestyle kick in action during the men's 1500 final at the 2004 Olympics:
As you can see in the swimming video above, the flutter kick is a simple and efficient kick used while swimming freestyle. Basically, both legs are kept parallel and quickly flutter up and down with toes pointed.
Flutter Kick Roles
The first role of the flutter kick is to provide propulsion. It is a fact that world class swimmers have a powerful kick. So it is clear that the kick has its importance in fast swimming. However, it might be less than you think. In fact, studies have shown that the amount of propulsion provided by the kick in elite swimmers is only about 10%. The rest of propulsion is provided by the arm stroke.
The second role of the flutter kick is to stabilize the body. In fact, the start of the propulsive phase of the arm stroke always coincides with a downward motion of the leg on the same side.
Let's now cover the flutter kick technique in more detail. The legs are kept parallel at all times and execute opposite movements: while one leg kicks downward the other one moves upward, and vice versa.
During the first half of the downbeat, the downward movement is initiated by slightly flexing the leg at the hip. Shortly after, the knee also bends a little bit. The foot goes in plantar flexion (toes pointed), both by muscle contraction and by the pressure of the water against the foot as it moves downward. During that phase, the top of the foot is oriented downward and a little bit backward. Because of this, while the foot moves down some water is in fact pushed back. That's how propulsion is generated in the flutter kick.
During the second half of the downbeat, the hip is locked in place while the knee is extended. The toes are still pointed. This phase isn't propulsive but prepares the leg for its upward movement.
The upbeat movement of the leg starts while the knee is still extending. In fact, while the leg moves upward, the pressure of the water against the lower leg will extend it. The pressure of the water against the bottom of the foot will also move it in an intermediary neutral position. This phase of the flutter kick isn't propulsive either.
There are two popular kicking rhythms in the freestyle stroke, the two-beat kick and the six-beat kick.
In the two-beat kick you kick once with each leg per stroke cycle. The downbeat of the right leg occurs during the propulsive phase of the right arm stroke (insweep and upsweep to be precise).
The two-beat rhythm is used by lots of middle and long distance swimmers because it uses less energy than the six-beat kick.
In the six-beat kick, each leg kicks three times per stroke cycle. Let's consider the movements of the right arm and the right leg. The first downbeat of the leg occurs during the forward extension of the arm. The second downbeat of the leg occurs during the upsweep of the arm. The third downbeat of the leg occurs during the recovery of the arm. The left leg moves in opposition to the right leg.
The six-beat kick is nearly always used by short-distance swimmers but is also popular with middle distance swimmers and long distance swimmers but with a somewhat subdued kick.
There are a few common mistakes in the flutter kick that decrease it's efficiency and hence should be avoided:
- Large kick: to keep drag to a minimum, the kick should stay within the hole opened in the water by the head and trunk while moving forward. Ideally, the kick should neither break the water surface nor move below the line of the body.
- Bicycle kick: during the downbeat, the kick is initiated by slightly flexing the hip and then the knee follows suit, also only bending a little bit. If you do bend the knee too much, the back of your lower leg will in fact move forward rather than upward. Water will then be pushed forward and slow you down.
- Putting too much force in the kick during the upbeat: in the freestyle stroke, the upbeat phase of the kick isn't propulsive. So ideally you should relax your leg during the upbeat to save energy.
- Bending your knee 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 have the tendency to bend your knee and point your toes, which wastes energy and increases drag. Ideally you should relax your leg so that the water pressure will extend it during the upbeat.
- If you have stiff ankles, it might be that your foot is only oriented downward or even downward and forward during the first phase of the downbeat. If that's the case, your kick might provide no propulsion at all or even have the tendency to move you backward rather than forward. This is often the case with people that have a running background. Using swimming fins and/or stretching regularly can improve the flexibility of your ankles.
- We have swimming exercises to learn how to flutter kick and balance in a prone position.
- An excellent exercise to improve your kick is vertical kicking.