The flutter kick is a kicking movement used in both

swimming Swimming is the self-propulsion of a person through water, or other liquid, usually for recreation, sport, exercise, or survival. Locomotion is achieved through coordinated movement of the limbs and the body to achieve hydrodynamic thrust that r ...

and

calisthenics Calisthenics (American English) or callisthenics (British English) ( /ˌkælɪsˈθɛnɪks/) is a form of strength training consisting of a variety of movements that exercise large muscle groups (gross motor movements), such as standing, graspi ...

Swimming

In swimming strokes such as the

front crawl The front crawl or forward crawl, also known as the Australian crawl or American crawl, is a swimming stroke usually regarded as the fastest of the four front primary strokes. As such, the front crawl stroke is almost universally used during a f ...

backstroke Backstroke or back crawl is one of the four swimming styles used in competitive events regulated by FINA, and the only one of these styles swum on the back. This swimming style has the advantage of easy breathing, but the disadvantage of swimm ...

, the primary purpose of the flutter kick is not propulsion but keeping the legs up and in the shadow for the upper body and assisting body rotation for arm strokes. The legs are extended straight backwards in line with the body. They are moved up and down, one leg kicking downwards (relative to the front of the swimmer's body) as the other leg moves up. The knees are slightly bent to facilitate the kicking action, but not too much in order to minimise drag created by the thighs as they move out of the shadow of the swimmer's body. Similarly, toes are pointed to minimize drag. The downward moving leg provides the thrust. An integral part of the kick is the flexing of the ankles; it is the flexing of the ankle that allows the foot to provide thrust. The knees are not kept rigid when kicking but are allowed to flex slightly to allow the required "snapping" action through the end of the toes.

Underwater diving

The flutter kick used with

swimfins Swimfins, swim fins, diving fins, or flippers are finlike accessories worn on the feet, legs or hands and made from rubber, plastic, carbon fiber or combinations of these materials, to aid movement through the water in water sports activities s ...

can be a powerful propulsion technique, and is used by

scuba divers This is a list of underwater divers whose exploits have made them notable. Underwater divers are people who take part in underwater diving activities – Underwater diving is practiced as part of an occupation, or for recreation, where t ...

and freedivers underwater and at the surface, but there are other finning techniques more appropriate to some underwater environments and some types of fin. Divers in a confined environment or where silting may be a problem may use a modified flutter kick or

frog kick Finning techniques are the skills and methods used by swimmers and underwater divers to propel themselves through the water and to maneuver when wearing swimfins. There are several styles used for propulsion, some of which are more suited to p ...

, done entirely with bent knees, pushing water up and behind the diver to avoid stirring up sediment on the bottom.

Calisthenics

The

version of the flutter kick is often used as an intensive training tool in the

military A military, also known collectively as armed forces, is a heavily armed, highly organized force primarily intended for warfare. It is typically authorized and maintained by a sovereign state, with its members identifiable by their distinct ...

. They help to develop the

hip flexors A flexor is a muscle that flexes a joint. In anatomy, flexion (from the Latin verb ''flectere'', to bend) is a joint movement that decreases the angle between the bones that converge at the joint. For example, one’s elbow joint flexes when one ...

abdominal muscles The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...

and leg muscles. Flutter kicks are a four-count exercise. Starting position is lying flat on the back with the feet and head approximately 6 inches (15 cm) off the ground. Hands are under the buttocks to support the lower back. Count one: raise the left leg to a 45-degree angle, keeping the right leg stationary. Count two: raise the right leg off the ground to a 45-degree angle while, at the same time, moving the left leg to the starting position. Counts three and four are repetitions of the same movements. Legs must be locked, with toes pointing away from the body."Military Ab Exercises - Flutter Kicks"
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References

Swimming styles {{swimming-stub