In a seated position with good posture, place a ball underneath your right arm in the armpit region so that it does not fall. Squeeze the upper arm and elbow onto the ball like a duck folding its wing, feeling the chest and arm muscles tighten as you squeeze. Do not bend at the waist. Release and repeat 8 to 10 times.
Switch to the opposite side and perform 8 to 10 repetitions. Rest briefly. Do another set of 8 to 10 repetitions on each side.