a speed version of the butterfly stroke.
In the initial position the swimmer’s arms and legs are extended and his face is under water. The arms supply the main propelling force by stroking simultaneously downward and to the rear. As the arms descend into the water, the wrists and elbows bend, the hands are brought somewhat closer together, and the speed of the stroke is increased. Upon completing the stroke, the swimmer rapidly brings his arms out of the water and moves them forward. Moving as close to the surface of the water as possible, the arms are then brought to about shoulder width and begin a new stroke. At the same time, the legs execute a rapid and elastic motion, or kick, pushing down on the water; the feet are turned in, increasing the resistance surface and the effectiveness of the kick. The knees are somewhat separated. Having completed the arm motion, the swimmer raises his legs to the surface and executes another kick. The swimmer inhales (through the mouth) at the end of the arm stroke and the beginning of the return motion of the arms above water; exhalation is under water.
In the most common variation of the dolphin there are two kicks, one inhalation, and one exhalation for each arm stroke.
N. A. BUTOVICH