A caved-in chest can develop if you have a protracted shoulder girdle, which occurs when your shoulders round forward due to persistently bad posture. Your upper and lower chest muscles may be short and tight. Weak muscles in the middle of your back might also contribute to a protracted shoulder girdle and caved-in chest. Exercises that stretch your chest and strengthen your back can reverse a caved-in chest that does not result from congenital deformities, such as pectus excavatum, which requires surgery.
Stretch your chest muscles by standing inside a doorway with the door frame at your sides. Raise one elbow to shoulder height with your arm bent 90 degrees. Place the forearm and palm of your raised arm against the wall that supports the doorway. Turn your body away from the raised arm. Hold the stretch for 10 to 30 seconds, then take one step back. Move your body closer to the door frame on the same side of your raised arm and place the front of your shoulder against the wall. Let the wall push your shoulder back as you lean forward and turn your body away from the raised arm. Hold the stretch for 10 to 30 seconds, then step back into the doorway to repeat both stretched positions with your other arm. Perform at least two sets.
Stand with your back up against a wall and your feet one step away from the wall. Your upper and lower back should be against the wall, and your hips and knees should bend slightly. Bend your elbows and place the back of your arms against the wall with your fingers pointing up. Slowly raise your arms along the wall as high as possible while pushing your shoulders and arms against the wall, and then slowly lower your arms back to starting position. Raising your arms against the wall stretches your pectorals and muscles in the middle of your back, including the rhomboids and trapezius. Repeat this exercise at least twice.
Stand a half step back and away from a doorway with the door frame closer to one side of your body. Bend the elbow closer to the door frame and place the inside of your forearm on the surface of the wall around the doorway. Position your elbow slightly below shoulder height with your fingers pointing up and your palm flat on the wall. Step forward into the doorway with the leg that is on the opposite side of your raised arm and step back with the other leg. Bend over forward at your hips and bend your knees slightly to stretch your subscapularis muscle, which is your primary rotator cuff muscle. Hold the stretch for 10 to 30 seconds and repeat at least two times.
Strengthen the trapezius and rhomboids in the middle of your back with rowing resistance exercises. Sit slightly forward on a bench that has a cable pulley attachment on one end. Grasp the cable attachment with both hands and rest your feet on the footrest platforms. Slide your hips back, and slightly bend your knees. Simultaneously pull the cable attachment to your waist and straighten your lower back; then pull your shoulders back as you push your chest forward and arch your back. Reverse the motion until your arms extend, your shoulders stretch forward and your lower back bends forward. Start with weight that exhausts your muscles in 12 repetitions and increase the weight only after you can perform unforced 15 repetitions. Perform at least two sets of this exercise.