Swimming provides a powerful cardiovascular workout combined with improved flexibility and increased your range of motion. Swimming also strengthens muscles throughout your body, from the obvious arms and legs, to the less obvious heart muscle and core. With all of the muscles engaged in every stroke, swimming freestyle will having you looking lean and long when you're out of the water.
Freestyle stroke works your arms and shoulders, creating a healthy, long, lean line. One arm goes over your head and back into the water as the other simultaneously propels you through the water. Your shoulders, biceps and triceps muscle groups all get a workout with this motion, as well as your hands, wrists and forearms when they flex and move with your arm. Freestyle also works out the deltoid muscle, or the rounded part of the shoulder, to keep your elbows up as you “catch” the water under you and use your arms to “pull” the water behind you.
Your legs kick and propel you forward as you move your arms, which means you're working out your hamstrings, calves, shins, quads, glutes and foot muscles. As you kick up and down, you engage your entire leg to aid in your freestyle stroke and speed. Your calves and feet, when streamlined, produce a flutter kick that propels you faster in the water. The rest of your leg muscles get a workout as you rotate your hips to maintain buoyancy and enable side breathing.
Because of the way your body moves while swimming freestyle, the core of your body is fully engaged. Pectoral muscle, the muscles of your chest; your oblique muscles, or the side muscles of your torso and abdominal muscles all help pull your arms through the water and also aid in your body rotation as you switch arms. Additionally, these muscles keep your body in a streamlined position during the recovery phase of the stroke -- they prevent you from swaying too much as you swim, resulting in a wiggle that slows you down. As you bring your arm out of the water, the movement affects the way your chest and hips move, so these muscles work overtime to stay centered.
Just as your core muscles work to keep you balanced, your back muscles aid in stabilizing your body throughout the your freestyle stroke. These muscles include your back, spinal cord support and rhomboid muscles, or your muscles directly below your neck in the center of your back. Plus, as you stretch outward with your arms and pull back to “push” the water behind you, the back muscles are the ones that feel that pull before you push.