Swimming improves your overall health and fitness, and looking good is an added benefit. You develop long toned muscles, but unlike weightlifting, swimming does not make you bulkier. The repetitive motions of swimming tend to make you stronger in certain areas than others, so mixing up your exercise routine helps prevent injury or pain from muscular imbalance.
Overall Muscle Use
Swimming is an aerobic exercise and engages the large major muscle groups in your body. You use both your upper and lower body to move through the water, though, you rely on the muscles of your upper body including the pectorals for propulsion in lap swimming. Because the leg muscles are large and energy-hungry, vigorous kicking tires you out quickly, and so you reserve it for sprints and races.
When you swim, you build up all the muscles in your upper back and chest, particularly the latissimus dorsi and internal rotators of the shoulder. Because the muscles bring the shoulders forward and inward, your pectoral chest muscles, or pecs, tend to tighten and shorten. Tense and contracted pectoral muscles further overstretch and eventually weaken the muscles surrounding the shoulder, leading to possible injury.
Muscular imbalance leads to postural changes and instability. Your upper back and your pectorals contribute to rotating your upper arms inward. Stretching out your pectoral muscles helps you counter the "slump back" that some dedicated swimmers develop. Mike Mejia, a coach and adviser on the USA Swimming website, recommends postural exercises to counter the repetitive movements you make during swim workouts. Pull your shoulders down and back, while slightly tucking your chin in and lifting your rib cage up and away from your abdomen to realign your posture and stretch out your pectorals. Other stretching exercises include arm swings, with and without torso rotation.
Building up your back and shoulders enough to develop posture imbalance takes a lot of time in the pool. Casual fitness swimmers benefit from all-over muscle tone, including the pecs. To build up your pectorals further, engage in alternative sports or specific exercises that expand and lengthen pectoral muscles, such as rowing. Exercising the external rotator-cuff muscles of the shoulders also helps balance out the strong internal rotators that swimming builds. It restores your pectorals to a comfortable length and stretch and helps keep your shoulders from rolling forward and your back from hunching over.
Swimming does not have as many injuries associated with it as more high-impact sports, but shoulder injuries do occur. Preventing injury requires stretching out and strengthening any weak muscles, including the pectorals. Building a strong abdominal core provides you with stability and a power base on which you build a strong and efficient swim stroke, according to Coachesinfo.com.