An Ode To Kicking Part I
Everyone seems to love kicking. ‘The legs build the stroke’ and all that.
There seems to be a blind acceptance that kicking is really important, and we all should be doing a lot of it.
However, there’s definitely been swimmers who have focused a lot on kicking and failed to improve their competitive performances. There are also coaches that have done no kicking, and had swimmers continue to improve.
I’d like to take a look at what we know about kicking to be true, and then use that information to draw conclusions about what we can do in training to improve performance efficiently and effectively.
As we’ll see, there are a lot of situations where a focus on kicking makes a lot of sense. The aim is to examine what these situations look like, and how our strategies might change depending on what we see in front of us.
While these ideas might not change what you do, they may change why you make certain decisions, and change when you choose to implement kicking. A thorough understanding can help you solve problems when your initial approach isn’t working.
Instead of deciding what to do and then justifying why it works, we’re going to build effective training practices from first principles. While many of these ideas have been demonstrated or validated in research contexts, we’re going to stick with what is self-evident, and base our conclusions on what we see happening in front of us every day.
Careful observation combined with simple logic can go a long way towards making better decisions.
Two quicks notes- this article series is primarily about flutter and dolphin kicking in the context of freestyle, backstroke, and butterfly. It is not about underwater travel (more here and here), and it is not about breaststroke kicking. Those two skills have different considerations and require a different approach.
Secondly, the easiest way to get visuals for everything discussed is to get on youtube.com and WATCH championship footage of world class athletes. NBC Sports and Universal Sports both of videos of the majority of World Championship and Olympic finals over the past decade. Many of the ISL races are available as well. Almost all of these clips have underwater footage. Watch it at full speed and in slow-motion. SEE what is going on.
Almost without exception, swimmers can swim faster when kicking than with the use of the arms alone. This has been demonstrated in research and in the experience of just about every coach. While there may be the occasional swimmer that can pull faster with a buoy than they can swim, a large part of that discrepancy is the buoy aiding flotation.
The difference tends to be about a 10% improvement in performance when swimming as opposed to swimming with the arms alone. This is obviously significant. As a result, swimmers kick during races, and they kick vigorously and consistently.
However, when you combine the respective speeds of kicking and pulling, they add up to more than the speed of the full stroke swimming. In terms of propulsion and speed, something is lost when full stroke swimming is performed.
Since swimmers have started to compete, coaches and athletes alike have wondered, how much do the legs contribute to swimming?
I’m not going to answer that question.
As referenced above, based upon some pretty simple testing that anyone can do, adding the legs improves speed by about 10%, with small differences between swimmers. This has been demonstrated on multiple occasions in highly controlled settings using the best technology available to us.
However, this doesn’t tell us the relative contributions of the arms and legs. It just tells us that swimmers are faster when they kick, and that’s why champion swimmers have a vigorous kick.
The contributions don’t matter. Swimmers should kick if they want to go faster.
What I would like to explore is WHY, and what that might mean for how we develop the legs for speed.
Why Kicking Might Work
Swimmers go faster when they add the legs. Here are several potential ways that kicking can improve speed.
As anyone who has ever used a kick board can tell you, propulsion can definitely be created by the legs. If you’ve moved forwards, you’ve created propulsion. There is definitely a strong possibility that at least some swimmers can create direct propulsion when they add the legs to swimming.
This is certainly true in breaststroke, highly likely in butterfly, and definitely possible in freestyle and backstroke.
Due to the wake that is left behind a swimmer’s bow waves, there tends to be a significant pressure gradient, with less pressure behind the swimmer than in front of the swimmer. A large front to back pressure tends to ‘pull’ the swimmer back, slowing velocity. Kicking may disrupt the wake, allowing for an improvement in velocity. It’s uncertain as to what degree the kick needs to be used to create this effect.
Better kicking is often cited as a tool to increase body alignment. At slow speeds, the legs tend to sink. However, this effect tends to disappear once swimmers reach common training and racing speeds. However, it’s possible that strong, downward kicking actions can create force that lifts the lower half of the body, creating a more horizontal alignment.
While the legs may not tend to sink due to torque on the legs, there is evidence that it is the pulling action of the arms that causes the legs to sink. When swimmers want to swim faster, they pull harder and faster. The harder and faster they pull, the more they will cause the legs to sink. To counteract these increasing forces, swimmers need to create more force through the kick. Faster swimming probably requires better kicking to balance this effect.
With every action there is an equal and opposite action. When performing arm strokes, there are linear, lateral, and rotational torques being applied during all pulling and arm recovery actions. These torques can potentially disrupt body alignment, and kicking can help to counteract these torques. In addition, appropriately timed kicks can help create additional torque to help swimmers pull through the ‘weaker’ phases of the arm actions. It’s almost like a quick turbo booster than is quite effective when timed right.
Watch any swimmer move through the water with a band around the ankles. The fluidity is lost. This is because the legs are unable to counteract the negative aspects of the arm actions. There is a loss of rhythm and alignment, and it takes much more work to get through the ‘hard’ parts of the arm action. This adds up to more resistance, less propulsion, and slower swimming.
Effective kicking can also stabilize the trunk. This accounts for some of the loss of fluidity seen when swimming with a band. The legs, and consequently the hips, are not stabilized and the torso starts to move, especially when stroke rates start to climb and there is more torque through the body. A weak kick can lead to an unstable torso, compromising body position and force production. A driving kicking keeps the hips and the torso stable, in spite of the actions of the arms.
This stable torso allows for smoother (not larger!) rotational actions. This facilitates faster recoveries with less lateral deviations. As importantly, a stable torso allows for stronger pulling actions. Better alignment and more power are going to allow for faster swimming. This starts from the kick.
As a side note, for those swimmers with really strange kicking actions, these are likely compensations for errors elsewhere in the stroke. Trying to directly change the aberrant kick is not going to be successful unless the underlying issue is addressed.
The observations about counterbalancing torque lead to an issue of timing. Effective kicking is about timing. When kicks happen is equally important as to how they happen. It is about the integration of the legs and the arms, with force being transferred through the torso from one limb to the other. The integration of the whole body is as important as the effectiveness of the actual kicking action.
As one leg is kicking at a time in freestyle and backstroke, each kick is going to create a rotational torque around the body. When timed effectively with the arm action, this rotational torque can help to ‘pop’ the hip over to the other side. While the hips are going to rotate due to the pulling and recovery actions of the arms, an effectively timed kick can help snap the rotation by helping to reduce the inertia of the kick.
If you watch champion swimmers in slow motion, you can see how when a leg kicks down, the torque travels up the leg into the hip and it subsequently pops up. At the same time the opposite arm is reaching forward at the front of the stroke. This is all part of the shift from one side to the other.
An effective two-beat is going to be timed so that each kick happens at an optimal time to rotate the hips. A full six-beat kick will also have one kick per side that serves this function. The remaining two kicks will counterbalance lesser torques present throughout the stroke cycle.
In freestyle most individuals settle into 6-beat or 2-beat kick timings, with a few further combinations that show up with less frequency. This is because these two major kicks serve to facilitate the side to side rhythm of freestyle. Most swimmers switch to a 6-beat kick at higher speeds, retaining this rhythm while also gaining the other benefits of kicking provided by a more significant kick (direct propulsion, wake disruption, hip stabilization, etc).
In backstroke, the same timing is present, although it is now an upkick that is facilitating the rotation of the hips, rather than a downkick. Further, almost all backstrokers retain a 6 beat kick as this is more conducive to the oppositional nature of the stroke (the arms are typically moving in direct opposition to each other).
Butterfly is a two-beat timing, with some swimmers omitting the kick upon entry of the arms or the kick upon exit of the arms. These kicks also serve to balance out the torques of the arms, move the hips (typically vertically), and allow for more effective arm actions. Again, these effects are magnified when timing is optimized.
For all strokes, the stroke rate of the arms is tied to the stroke rate of the kick. If the kick rate cannot keep up the stroke rate, the stroke rate is going to be limited by how fast the legs can complete the kicking cycle. Failure to keep the kick and arm cycles in rhythm will result in a dramatic loss of efficiency and speed. Swimmers of reasonable skill level tend to avoid this situation.
Ineffective timing can be improved. By simply changing WHEN kicking happens relative to the arms, we can improve kicking effectiveness without any change in leg fitness or kick quality. Great kicking, at least when it comes to swimming fast, is as much a timing issue as anything else.
Simply kicking on a board isn’t going to solve this problem.
Some conclusions so far-
Kicking may reduce drag through disrupting the wake the flows into low pressure areas behind a swimmer. However, exaggerating the kick will create more drag than it reduces.
Kicking serves more functions than just propulsion. It is a critical component in counterbalancing the forces created by the upper body, reducing drag and magnifying force production.
If swimmers are unable to effectively time the kicking action, not only will their kick be ineffective, they will swim slower than possible as they are working ‘against themselves’.
Trying to ‘overkick’ is not efficient, as kicking more than rhythm and rate allows for disrupts the fundamental rhythm and timing of the strokes.
If the legs are unable to sustain the kicking rhythm required to swim at the desired stroke, the arm cycle will slow to keep maintain timing, or swimmers will lose their timing. Both situations result in a loss of velocity.
While propulsion is possible from the legs, it is only possible up to a point before timing is impaired and drag creation is increased.
Clearly there is a limit as to how hard someone can kick before it becomes counterproductive. It is about fitting the kick into the rhythm and timing of the stroke. It is about optimal as opposed to maximal.
However, swimmers can get some propulsion from their kicking. In part II, we’ll take a look how swimmers can improve the propulsion they can get from their kick, while ensuring that the kick still functions as an effective component within full stroke swimming.