Freestyle
By definition, freestyle events permit athletes to use any style of swimming they choose. However, one technique, the front crawl, is so widely used during freestyle competitions that it is practically synonymous with the term "freestyle."
The front crawl is characterized by an alternating overhand motion of the arms and a flutter or scissor kick. Athletes use their arm motion to pull themselves through the water, while the kicking tempo provides additional propulsion. Breathing patterns vary depending on the distance of an event and an athlete's preferred method. In the 50m freestyle, for example, some competitors don't breathe at any point during the race.
Freestyle swimming has been included in every modern Olympics. Currently, freestyle is contested in more Olympic events than any other stroke, at distances of 50m, 100m, 200m, 400m, 800m, and 1500m. There are also two freestyle relay events per gender, a 4x100m and a 4x200m.
SEE MORE: Rio 2016: Simone Manuel ties for gold in 100m free, new OR
Backstroke
The backstroke, like the front crawl, combines an alternating motion of the arms with a flutter kick, but is done with the face and chest facing upwards out of the water.
While the three downward-facing strokes allow athletes to track their position in the pool by looking at a black line on the pool floor, backstrokers must find their own reference point with which to orient themselves. At indoor facilities, like the Tokyo Aquatics Center, this is often a spot on the ceiling. Outdoor pools can pose a greater challenge.
The backstroke was first contested at the 1900 Paris Games. Current Olympic distances are 100m and 200m.
SEE MORE: Rio 2016: Ryan Murphy extends U.S.'s 100m backstroke streak
Breaststroke
The breaststroke is a highly technical stroke and is therefore difficult to master. It is the slowest of the four Olympic strokes. The arms must move simultaneously in mirrored forward-then-outward-then-backward circles. Throughout this motion the elbows remain underwater. The kick is a simultaneous thrust of the legs called a "frog" or breaststroke kick. No flutter or dolphin kicking is allowed, except for one dolphin kick going into and coming out of each turn.
Except for after the start and turns, some part of the swimmer's head must come above water during each cycle of a stroke and kick. Touching the wall at turns or the finish must be done with both hands simultaneously.
The breaststroke, which first appeared at the Olympics in 1908, is contested over distances of 100m and 200m.
SEE MORE: Rio 2016: Lilly King beats Yulia Efimova in 100 breaststroke
Butterfly
The most powerful and physically demanding stroke, the butterfly, involves simultaneous overhead swinging of the arms combined with a dolphin kick. The dolphin kick involves both legs moving up and down together like a mermaid's tale. No flutter kicking is allowed. The butterfly is visually impressive, as athletes often appear to be leaping out of the water with each stroke.
The butterfly technique initially developed from breaststroke, when swimmers would recover their arms above the water instead of beneath it. Butterfly became an independent stroke and made its Olympic debut at the 1956 Melbourne Games. The stroke is contested over distances of 100m and 200m.
SEE MORE: Rio 2016: Michael Phelps takes back 200m butterfly gold
Medley
In swimming, the term “medley” refers to events that incorporate all four strokes in the same race. There are two kinds of medley events, individual and relay.
The individual medley (IM) requires competitors to use each stroke for one-fourth of the race, following this sequence: butterfly, then backstroke, then breaststroke, then freestyle. There are two IM distances in the Olympic program, 200m and 400m.
The medley relay features teams of four, where each team member swims a different stroke. Teams are usually comprised of a country’s fastest individual swimmer in each stroke. The medley relay sequence is backstroke, breaststroke, butterfly, freestyle. New to the Tokyo Games is the mixed medley relay, which features teams of two men and two women.
SEE MORE: Rio 2016: Michael Phelps wins fourth and final 200m IM
