Sit on a stability ball with your feet flat on the floor and core engaged. Lean your upper back against the ball while maintaining a neutral spine. Extend your arms out to the sides at shoulder height with a slight bend in the elbows. Allow your chest to open as your arms move slightly backward, either assisted by a partner or resistance (e.g., band), until you feel a stretch across your chest. Hold the position for 15–30 seconds while breathing steadily, then return to the starting position with control.
Log your assisted seated pectoralis major stretch with stability ball sets in 1RM.fit and watch your estimated 1RM update automatically as you get stronger.