Muscle structure of a swimmer

Written by claire lunardoni
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Muscle structure of a swimmer
(© Paylessimages -, Anatomical Diagrams submitted to Wikimediacommons by Mikael Häggström with modifications by the author)

All four of the competitive strokes--freestyle, backstroke, breaststroke and butterfly--use every major muscle group in the body, making swimming a full-body workout. The muscles in the upper back (latissimus dorsi, trapezius and rhomboids), arms (biceps, triceps and forearm muscles), shoulders (deltoids) and chest (pectorals) are the primary movers in the pulling action. Each stroke uses the muscles differently and to varying degrees. To watch these muscles in action, click on the "AnyBody" link in the Resources section.

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Core Muscles

The "core" muscles in the abdomen and lower back are as important in swimming as the muscles in the upper body. Core muscles are responsible for the side-to-side rolling in the long axis strokes (freestyle and backstroke) and the wavelike movement in the short axis strokes (butterfly and breaststroke). A strong trunk also is important to maintain a streamlined position and to maximise the power transfer from the upper body to the lower body.

A flip turn is like an ab crunch with water resistance. To somersault your body and plant your feet on the wall, your rectus abdominis (abs) must contract forcefully to generate enough power for your legs to flip over your head. Without sufficient ab strength, flip turns are slow and crooked.

Muscle structure of a swimmer
The large muscles of the body from the front (common nicknames provided in red)

Lower Body

Kicking works the muscles in your hips and legs. The primary movers in the flutter kick--used in the backstroke and freestyle--are the glutes, hamstrings and quadriceps. The dolphin kick (or butterfly kick) is just like a flutter kick with your legs stuck together and uses the same muscles. The "frog" or "whip" kick used in the breaststroke works the same muscles as the flutter and dolphin kicks but also recruits your hip adductors, the muscles on your inner thighs that pull your legs together.

Powerful leg muscles also are important in other aspects of swimming: starts and turns. When leaping off the starting blocks or springing off the wall, your leg muscles must contract forcefully to launch you through the water. The more powerfully you push off the blocks or wall, the more momentum you have when you begin swimming. The large muscles in the butt and thighs provide most of the power in starts and turns. Calves flex the foot, providing the finishing drive as the feet snap off the wall or blocks.

Shoulder Injuries

The shoulder is a complex joint (four joints, actually), and it is the only joint in the body besides the hips that can move on all three dimensions. Small, delicate muscles surround the shoulder. Because the shoulder can move in so many directions and is protected only by small muscles, it is an unstable joint.

Swimming involves moving the fragile shoulder against a lot of resistance, sometimes leading to injury. A study by Sien et al. at the Orthopaedic Research Institute in Australia found that the incidence of shoulder pain increases as swimming volume increases. If you develop shoulder pain while swimming, take a few days off and reduce overall swimming volume. If the pain continues, consult a qualified swimming coach to evaluate your technique.

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