At The Race Club we have always preached about the importance of the kick in contributing to one’s overall swimming speed. I call it the Y factor, because the kick is generally why great swimmers swim fast.
In order for the flutter or dolphin kick to be really strong, one needs to have or develop great plantar flexibility in the ankle. One also needs to learn the proper kicking motion, emanating from the hips and core, not from the knees down. Then, one needs to develop leg strength and leg fitness to be able to sustain the correct motion relentlessly throughout the race.
I have written in the past about the four different functions of the swim kick, propulsion, lift, stabilizing counter force for the end of the underwater pull, and a way to observe the immutable law of inertia…or to help keep the speed more constant.
The upkick in freestyle and dolphin, the weaker of the two directions, is the most neglected part of the kick. Kicking is not easy, so It is natural to look for some recovery period in the kick and it seems logical to choose the upkick for this opportunity, since it produces less propulsion than the downkick for a similar effort. So why not just kick down with a tremendous force and let the feet drift back up for another good down kick?
I have always reasoned that the law of inertia, trying to keep the object in motion and maintaining a more constant speed in the water, was a good enough reason to work both the upkick and the downkick. Then, even if the propulsive force is less with the upkick, by applying pressure on the water in both directions, creating some propulsion nearly all of the time, would lead to a more constant speed and more efficient swim. But there is another reason to work the upkick, perhaps even more important than trying to obey the law of inertia.
When fish swim with their tails, they push equally hard in both directions from side to side. As the tail moves through its path it creates a wake or vortex behind it, which, depending on the size of the fish, can extend for several feet behind the tail. Once the fish completes the path of the movement in one direction, it immediately moves the tail back in the opposite direction. Because the wake or vortex follows the tail, the tail pushes back against a stream of water flowing in the opposite direction, or toward the tail. By pushing back against this stream of flowing water, the tail is more effective and the propulsion more powerful than if it were simply pushing against still water.
If one chooses to take a vacation on the upkick and relax the motion of the feet drifting upward, when the downkick is initiated, there is no stream to push against. The net propulsive force of the downkick is not as strong as it would have been if the upkick had been strong, creating a wake behind it.
Here’s the rub. If you want to be an effective and fast kicker, you have to kick hard in both directions. If you are swimming a 50 m sprint and your stroke rate is 120 strokes per minute (cycle rate of 60), your kick rate is 12 x 60 or 720 kicks (including upkicks and downkicks) per minute….and there is no recovery time (except perhaps a half second on each turn). That is not quite as fast as a hummingbird wing moves, but it is pretty fast.
The point is that moving at that speed and with no recovery time, your legs need to be relatively fitter than your arms. So start working your legs more, kicking in both directions, and then start swimming faster.
Yours in swimming,