Why Stretch the Pec Major Before Exercise? The pectoralis major often becomes shortened and overactive due to poor posture, desk work, and repetitive pressing movements. Stretching it prior to exercise helps restore shoulder mobility, improves scapular positioning, and reduces compensatory tension in the neck and upper traps. A properly lengthened pec major also allows for better thoracic extension and arm mechanics—critical for safe, efficient movement in both pushing and pulling exercises. . W