Dr. Jason B. Kaster Shows How to do a Pectoralis Stretch or exercise. Pectoralis Stretch is helpful for individuals with forward, rounded, and internally rotated shoulders. Typically seen with large breasted women, thoracic outlet syndrome, those who work or sit at a desk for long periods; and seen with individuals with poor posture where their middle back is slumped forward known as kyphosis. In addition, weight lifters who focus on their chest verses back when working out, typically have protracted or forward / rounded shoulders.