The side stretch exercise stretches and strengthens the intercostal muscles, (the muscles between the ribs), which help support the ribs. To do the side stretch:
Sit in a sturdy chair with your feet flat on the floor.
Lean forward slightly to keep from "hunching" your back and shoulders.
Keep your hips, shoulders, and ears in a straight up-and-down line.
Raise your right arm overhead and bend your upper body to the left in a reaching motion. Keep your upper body facing straight ahead—don't twist it to the side as you bend.
Make sure you feel the muscles gently stretch all along your side from your lower back up to your shoulder.
Hold the stretch for 20 seconds, then return to the starting position. Repeat the stretch two times.
Switch sides and do the stretch in the opposite direction, repeating twice.