When you are swimming the breaststroke, water provides resistance --- but it's a level of resistance you cannot change. You can't make water thicker or thinner, so once your muscles adapt to the breaststroke, the improvement you are likely to see in the strength of your muscles is limited. Land-based weight-training exercises will continue to strengthen your upper body and improve your breaststroke ability. Consult your doctor before beginning any new exercise regimen.
The breaststroke requires upper-body strength, with your chest, back and front of the upper arms used perform the movement, according to the National Strength and Conditioning Association. Your chest contains your pectoralis major. Your back uses the large latissimus dorsi muscle and your upper arms contain your biceps. To effectively strengthen these muscles, perform one to three sets of eight to 12 repetitions each of each exercise. Your muscles need at least one day of rest between strength-training workouts for recovery.
You can strengthen the biceps muscles of your upper arm with arm curl exercises. You hold a dumbbell in each hand for an arm curl, and change the muscle focus by changing the position of your palms. An arm curl, for example, is performed when you bend a straight arm to raise the dumbbell toward your shoulders; a hammer curl has your palms facing each other as you raise and lower the dumbbells.
An effective exercise to strengthen your back and your arms is a chinup. The difference between a chinup and a pullup is hand placement. During a chinup, your palms are facing each other, which requires a greater muscle contraction from your arms during the movement. You will need a high chinup bar from which to hang, with your arms extended and your legs either straight beneath you or your feet behind you and your knees bent. Perform a chinup by bending your elbows and lifting your chin up to the level of your hands.
A pushup will strengthen your upper body, including your chest, to enhance the power of your breaststroke. A traditional pushup begins with your hands and feet on the floor and your body in a straight line. Bend your elbows to lower your body toward the floor, then straighten your arms to press your body up. Increase the intensity of a pushup by lifting one foot at a time off the floor, the American Council on Exercise suggests.