Swimming stroke

Human swimming typically consists of repeating a specific body motion or swimming stroke to propel the body forward. There are many kinds of strokes, each defining a different swimming style or crawl.
In high school, collegiate, and Olympic swimming, there are two undulating strokes (breaststroke and butterfly stroke) and two alternating strokes (front crawl and backstroke).
Most strokes involve rhythmic and coordinated movements of all major body parts — torso, arms, legs, hands, feet, and head. Breathing typically must be synchronized with the strokes, too. It is possible, however, to swim by moving only legs without arms or only arms without legs; such strokes may be used for special purposes, for training or exercise, or by amputees (paralympians) and paralytics.
Within a competitive sense particularly, swim stroke techniques are continuously changing to become either easier or more efficient as more people explore the activity.
A study done by Barbosa Tiago M. in a study called Energetics and biomechanics as determining factors of swimming performance: Updating the state of the art. This text discusses the relationship between segmental kinematics and center of mass kinematics in competitive swimming, focusing on how stroke length (SL) and stroke frequency (SF) influence swimming velocity (v) and performance. Freestyle is the fastest stroke, followed by Butterfly, Backstroke, and Breaststroke, with performance variations depending on distance and stroke technique. A decline in velocity during a race is linked to a decrease in SL, with greater reliance on SF for speed when SL is short. High-level swimmers maintain higher and more stable spatial-temporal parameters, particularly in Freestyle, where SF variability is lower than in Backstroke. Across laps, both genders exhibit a “zig-zag” pattern in SF, peaking during the final lap, with this pattern being more pronounced in males and less variable among elite swimmers. A study done by Rejman Marek called Goggle-free swimming as autonomous water competence from the perspective of breath control on execution of a given distance. The study explored adolescents’ ability to maintain breathing rhythm while swimming with and without goggles, emphasizing water competence over stroke techniques. Results showed that the absence of goggles negatively impacted breath control for both genders, with boys struggling more to swim effectively and safely. The study recommends incorporating goggle-free swimming into elementary education, focusing on simple forms of swimming for breath control training, and accounting for gender differences in visual perception and motor control during instruction.
A number of strokes are only used for special purposes, e.g. to manipulate an object (a swimmer in distress, a ball), or just to stay afloat.
Swimming underwater is faster than swimming on the surface. Underwater swimming is not its own category in the Olympics, but in the 1988 Olympics several competitors swam much of the backstroke race underwater. After that, the Olympics created a rule that swimmers are only allowed to stay underwater for the first 10 meters (later changed to 15 meters) after a start or a turn.
Any style with underwater recovery can be done underwater for certain distances depending on the need for air. Underwater swimming on the back has the additional problem of water entering the nose. To avoid this, the swimmer can breathe out through the nose or wear a nose clip. Some swimmers can close their nostrils with the upper lip or with the compressor naris muscles.
Barbosa et al., “Energetics and Biomechanics as Determining Factors of Swimming Performance.” Rejman, Rudnik, and Stallman, “Goggle-Free Swimming as Autonomous Water Competence from the Perspective of Breath Control on Execution of a given Distance.”