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: