What is the Dolphin Kick?
The dolphin kick is the kicking technique performed in the butterfly stroke. The legs move in sync and perform movements similar to a dolphin’s tail, hence explaining the name.
The dolphin kick consists of two phases:
- The downbeat, where the legs move downward and provide propulsion.
- The upbeat, where the legs move up in preparation for the next downbeat.
The swimmer performs two dolphin kicks per butterfly stroke cycle.
More explanations are provided below.
Underwater Dolphin Kick Video
In the following video, we can see Michael Phelps and Chris Thompson swimming in the butterfly style and performing the underwater dolphin kick:
Both swimmers have amazingly flexible ankles. We can also see that Michael Phelps’s body undulation amplitude is greater than Chris Thompson’s.
The downbeat is the propulsive phase of the dolphin kick. The downbeat starts at the end of the previous upbeat, when the legs are fully extended and the feet move above the level of the body. The sequence is as follows:
- The swimmer pushes his hips down, and the thighs follow along. Meanwhile, the knees flex, and the lower legs continue to travel up. The pressure of the water against the feet causes them to extend.
- The swimmer flexes his hips and continues to flex his knees. The lower legs continue to move up. This initiates the propulsive whip-like movement of the legs.
- The swimmer extends his knees, which causes the lower legs to move down quickly and forcefully, like cracking a whip.
- The downbeat ends when the legs are fully extended and the feet are below the level of the body.
An effective dolphin kick requires flexible ankles. This allows the top of the feet to be facing downward and backward instead of just downward during the downbeat. Consequently, water can be pushed backward in addition to downward, creating propulsion.
The upbeat begins at the end of the previous downbeat. The sequence is as follows:
- At the end of the previous downbeat, the knees extend, and the lower legs and feet move down, pushing against the water. In reaction, the hips of the swimmer move up.
- Once the feet are below the level of the body, the swimmer uses the momentum of his hips moving up to initiate the upbeat. He simply extends his hips, and as a consequence, the thighs begin to move up.
- The downward pressure of the water against the lower legs causes the knees to extend. Furthermore, the feet assume a neutral position, partly flexed and partly extended.
- The extended legs move up until the feet are above the level of the body. At that point, the next downbeat begins.
The upbeat is not propulsive because, during that phase of the dolphin kick, the lower leg and bottom of the foot are facing upward and forward.
Consequently, using unnecessary force during the upbeat would only cause water to be pushed upward and forward, wasting energy and creating drag.
Number of Kicks per Stroke Cycle
As mentioned above, there are two kicks per stroke cycle. These dolphin kicks are synchronized with the butterfly arm movements:
- The propulsive downbeat of the first kick occurs at the end of the arm recovery, when the arms enter the water in front of the shoulders and extend forward underwater.
- The upbeat of the first kick occurs at the end of the outsweep and during the insweep of the arms toward the chest.
- The propulsive downbeat of the second kick occurs during the upsweep of the arms, from below the chest toward the hips. This downbeat counteracts the tendency of the hips to drop during the upsweep of the arms.
- The upbeat of the second kick occurs during the release of the arms from the water and their recovery forward. This upbeat helps to lift the head and shoulders above the water surface.
In most cases, the first dolphin kick is more propulsive and lasts longer than the second one.
- If you have stiff ankles, the regular practice of ankle stretching exercises and the use of short swim fins can help loosen up your ankles. This will improve your propulsion in butterfly, but also in front crawl and backstroke.
- We have a specific set of exercises to learn the body undulation and dolphin kick. These can be handy if you find it hard to learn these techniques.
Maglischo, E. (2003). Swimming Fastest. Champaign, IL: Human Kinetics, pp. 161-165.
You may also be interested in the following articles that cover the butterfly stroke’s swimming technique:
Friday 17th of December 2021
On what scientific base do you write all that?
You don't speak about the upward kick.
You say to start with the movement of the head but the head and shoulder line shouldn't move during dolphin kick.
I don't understand your articles at all.
Bob Bowman, Michael Phels coach : https://www.youtube.com/watch?v=Bepnpr5bD0M
you can see al the details of the motion and the muscle use on this articles from japan scientist in elite butterfly swimmer. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7739797/
And if you want to know more about the propulsion and how it works (because it sure isn't the downward kick that push water behind but the synergy of vortices that create the propulsion.) http://simonbaumann.fr/underwater-undulatory-swimming-uus/
Please stop spreading misinformation.
I stay at you disposal if you want to talk about it.
Wednesday 22nd of December 2021
My reference is Ernest W. Maglischo's "Swimming Fastest" (https://www.amazon.com/Swimming-Fastest-Ernest-Maglischo/dp/0736031804/)
On the dolphin kick, he writes on page 86:
"The upbeats of the front crawl flutter kick and the dolphin kick are probably not propulsive." ... "Kick patterns drawn from films of world-class athletes swimming at competitive speeds show that their feet travel upward and forward during the upbeat in the butterfly and upward, forward, and laterally during the front crawl. Leg movements in these directions should actually inhibit rather than increase propulsive force because of the counterforces they produce in downward, backward, and lateral directions."
On body undulations, Ernest W. Maglischo writes on page 166:
"Most people think that body undulations are centered in the hips during butterfly swimming. In reality, however, the vertical movements of the head and shoulders actually exceed those of the hips (Sanders, Cappaert, and Delvin 1995). The precise sequencing of vertical head movements appears to be the major player when proper undulation is concerned."
On the Bob Bowman video https://www.youtube.com/watch?v=Bepnpr5bD0M one can see that the swimmer's shoulders travel up and down during the body undulation.
In the paper https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7739797/ the author(s) write(s):
"This synergy, which is activated during the upward kick, is thought to contribute to knee flexion and ankle plantarflexion, and propulsion is generated by kicking the water upward."
I have to agree with Ernest W. Malgischo, I fail to see how kicking water upward would provide propulsion.
On fling-ring/vortex propulsion, Ernest W. Maglischo writes the following on pages 17-18:
"The vortex theory of swimming propulsion is based on sound principles of aerodynamics. If it actually operates during human swimming, it would mean that lift forces make a considerable contribution to propulsion even when the boundary layer separates. Unfortunately, there are many difficulties associated with proving or disproving this theory.
The major problem in proving this theory is determining whether swimmers can actually establish a bound vortex around the hands and feet during their underwater propulsive efforts. If a bound vortex cannot be maintained, even for short distances, its effect on increasing lift force and vortex shedding would not be available for foil and fling-ring propulsion.
Vortices are certainly visible trailing off the hands, arms, and feet of swimmers. Nevertheless, there is no proof that these trailing masses of turbulent water result from the creation and shedding of bound vortices. In fact, the available evidence indicates that a bound vortex will not develop around such small and poorly streamlined objects such as swimmers' hands and arms. A bound vortex needs time to develop and the fact that the boundary layer separates so quickly as it passes over the human hand makes it doubtful that there will be enough time to form a starting vortex that develops into a bound vortex."
Furthermore, on page 171:
"As explained in chapter 1, it is doubtful that swimmers actually gain propulsion from the production and shedding of vortices with the legs. Certainly, they accelerate some water backward with the kick, which in turn accelerates them forward. At the same time, the water behind them becomes turbulent when they kick against it. Nevertheless, this does not mean that they are shedding organized vortices backward with sufficient intensity to propel them forward. Even if they could, those vortices would probably dissipate so rapidly that most, if not all, of the effect would be lost almost immediately after the vortices were shed. In other words, any propulsive effect would occur immediately after the vortices are shed backward and they would dissipate soon after."
I’m not a scientist, so I won’t argue with you if vortex propulsion is a thing or not in human swimming. If you want to discuss the subject, I think it is better to do so with people like Ernest W. Maglischo.
No, as far as the movements of the head and shoulders in butterfly swimming are concerned, I have seen videos of monofin swimmers before, and to be fair, they indeed try to minimize the movements of the head and shoulders in their underwater swimming.
But I’m not sure this makes sense for regular butterfly swimming, except maybe for the underwater phase after starts and turns.
And I think for beginners, it is essential that they drive the body undulation with their whole body, from head to toes, when they try to learn this technique, as shown in the head-lead body dolphin drill.
Once the beginner is able to move forward using only the body undulation, learning the rest of the butterfly technique becomes much easier.
All the best,
Wednesday 17th of July 2019
Thanks for this website. I am trying to learn to swim at age 66. It is not easy and is complicated by my extremely weak left leg. It suffered nerve damage in an accident a few years ago and has never recovered. I am hoping that swimming will strengthen it at least a little and will improve my cardio function, which is also compromised.
I am a bit overwhelmed by the various strokes and movements and have some difficulty following them with my damaged leg. But your site is great for seeing how things *should* work. Any suggestions for coping with the bad leg?
Thanks again! The videos are terrific.
Thursday 18th of July 2019
At my local pool we have a guy who has lost one of his legs in an accident. What he does is that he puts a long swim fin on his other leg to compensate and swims front crawl in that fashion.
I think trying to learn front crawl using a single fin on your weak leg or even a pair of fins might be worth a try. I think you should be able to do the drills for learning the front crawl in that way.
Tuesday 2nd of April 2019
What is downbeat and upbeat for dolphin kick?
Monday 4th of February 2019
This helped a lot!
Friday 20th of April 2018
What happens when you separate your legs during the dolphin kick?
Friday 4th of May 2018
You defy the whole movement flow. My childhood swim instructor used to wrap tie my ankles so I could not separate legs...
So thankful to her to this day :-)
Sunday 22nd of April 2018
I think there will be less propulsion because you have less grip on the water.