The butterfly technique with the dolphin kick consists of synchronous arm movement with a synchronous leg kick. Good technique is crucial to swim this style effectively. The wave-like body movement is also very significant, as this is the key to easy synchronous over-water recovery and breathing.
Technique
In the initial position, the swimmer lies on the breast, the arms are stretched to the front, and the legs are extended to the back.
Arm movement
The butterfly stroke has three major parts, the pull, the push, and the recovery. These can also be further subdivided. From the initial position, the arm movement starts very similarly to the breast stroke. At the beginning the hands sink a little bit down with the palms facing outwards and slightly down at shoulder width, then the hands move out to create a Y. This is called catching the water. The pull movement follows a semicircle with the elbow higher than the hand and the hand pointing towards the body center and downward. The semicircle ends in front of the chin, with the hands close together so the swimmer can form a triangle with the fingers.
The push pushes the palm backward through the water underneath the body at the beginning and at the side of the body at the end of the push. The swimmer only pushes the arms 1/3 of the way to the hips, making it easier to enter into the recover and making the recovery shorter and making the breathing window shorter. The movement increases speed throughout the pull/push phase until the hand is the fastest at the end of the push. This step is called the release and is crucial for the recovery. The speed at the end of the push is used to help with the recovery.
The recovery swings the arms sideways across the water surface to the front, with the elbows slightly higher than the hands and shoulders. The arms have to be swung forward fast in order to bring them to the front over the water. It is important not to enter the water too early, because this would generate extra resistance as the arms moved forward in the water against the swimming direction. A high elbow recovery, as in front crawl, would save more energy, yet the movement restrictions in the shoulders do not allow this easily, and due to the synchronized movement it is not possible to roll around the shoulders as in front crawl.
The arms enter the water with the thumbs first at shoulder width. A wider entry loses movement in the next pull phase, and a smaller entry, where the hands touch, wastes energy. After a brief rest the cycle repeats with the pull phase.
Generally, viewed from below, the arm movement forms a fat "keyhole" figure during the stroke cycle in the water. However, more recently, a straighter arm pull has been favoured in competitive swimming.
Leg movement
The leg movement is similar to the leg movement in the front crawl, except the legs are synchronized with each other. The shoulders are brought above the surface by a strong up and medium down kick, and back below the surface by a strong down and medium up kick. A smooth undulation fuse the motion together.
The feet are pressed together to avoid loss of water-pressure. The feet are naturally pointing downwards, giving downwards thrust, moving up the feet and pressing down the head.
There is no actual stipulation in competitive butterfly rules that a swimmer make a fixed number of pulses in butterfly–the swimmer may kick as little or as much as he or she may wish. While competitive rules allow such a choice, the typical method of swimming butterfly is with two kicks.
As butterfly originated as a variant on breaststroke, it would be performed with a breaststroke or whip kick by some swimmers. While breaststroke was separated from butterfly in 1953, the breaststroke kick in butterfly was not officially outlawed until 2001. However a number of Masters swimmers were upset with the change since they came from a time when butterfly was usually swum with a breaststroke kick. FINA was then convinced to allow a breaststroke kick in Masters swimming. Given the option, most swimmers choose to use a dolphin kicking action, but there still is a small minority of swimmers who prefer the breaststroke kick, for recreational swimming and even for competition.
Breathing
There is only a short window for breathing in the butterfly. If this window is missed, swimming becomes very difficult. Optimally, a butterfly swimmer synchronizes the taking of breaths with the undulation of the body to simplify the breathing process; doing this well requires some attention to butterfly stroke technique. The breathing process begins during the underwater "press" portion of the stroke. As the hands and forearms move underneath the chest, the body will naturally rise toward the surface of the water. With a minimum of effort, the swimmer can lift the head to break the surface fully. The swimmer breathes in through the mouth. Experienced swimmers continue looking toward the bottom of the pool while they inhale to keep the body balanced and in a straight line. The head goes back in the water after the arms come out of the water as they are swinging forward over the surface of the water. If the head stays out too long, the recovery is hindered. The swimmer breathes out through mouth and nose till the next breath. Some swimmers, most notably Denis Pankratov, breathe to the side as in the front crawl, but their timing is otherwise the same. Such a style of breathing is quite uncommon though and generally discouraged by coaches.
Normally, a breath is taken every other stroke. This can be sustained over long distances. Oftentimes, breathing every stroke slows the swimmer down. (At a certain level, the stroke with a breath and the stroke without a breath become synonymous in their speed; therefore, very experienced competitors - such as Michael Phelps - may breath every stroke.) Other intervals of breathing practiced by elite swimmers include the "two up, one down" approach in which the swimmer breathes for two successive strokes and then keeps the head in the water on the next stroke, which is easier on the lungs. Swimmers with good lung capacity might also breathe every 3rd stroke during sprints or the finish. Some swimmers can even hold their breaths for an entire race (assuming that it is a short one).
Body movement
Swimming the arms or the legs separately is difficult, and correct body movement is great for the arms and legs to use their full potential. The body moves in a wave-like fashion, controlled by the arm movement. As the hands go in, the hips go up, and the posterior breaks the water surface. During the push phase the head goes up and the hips are at their lowest position. In this style, the second pulse in the cycle is stronger than the first pulse, as the second pulse is more in flow with the body movement.
Start
Butterfly uses the regular start for swimming. After the start a sliding phase follows under water, followed by dolphin kicks swum under water. Swimming under water reduces the drag from breaking the surface and is very economical. Rules allow for 15 m of underwater swimming, before the head must break the surface, and regular swimming begins.
Turn and finish
During turns and during the finish, both hands must simultaneously touch the wall while the swimmer remains swimming face down. The swimmer touches the wall with both hands while bending the elbows slightly. The bent elbows allow the swimmer to push himself or herself away from the wall and turn sideways. One hand leaves the wall to be moved to the front underwater. At the same time the legs are pulled closer and moved underneath of the body towards the wall. The second hand leaves the wall to be moved to the front over water. It is commonly referred to as an "over/under turn" or an "open turn." The legs touch the wall and the hands are at the front. The swimmer sinks under water and lays on the breast, or nearly so. Then the swimmer pushes off the wall, keeping a streamline position with the hands to the front. Similar to the start, the swimmer is allowed to swim 15m underwater before the head must break the surface. Most swimmers dolphin kick after an initial gliding phase.
The finish requires the swimmer to touch the wall with both hands at the same time, in the same horizontal plane.