The Pec is not really an internal rotator.

A degree of internal rotation may be part of the arm path depending on the humeral orientation, but any internal rotational force of the pec is only a faction of the the main force pulling its insertion towards the origin, which is best described as varying degrees/angles of adduction and flexion, but more importantly understanding these movement beyond their nomenclature is the key to understanding functional anatomy, which is what is needed to understand biomechanics and training. Membership Site with the most innovative Exercise Library, Articles, Videos, and Workout & Nutrition Programs www.N1.Training Shirts & Steel Shakers www.N1.Training/Merch Online Courses and Live Practical Events/Seminars www.N1.education N1 Education gives trainers, coaches, and fitness enthusiast  the most complete and efficient education to set themselves apart from all others.  Don't settle for a book or a course, N1 gives you an entire curriculum that is easy to apply to training and nutrition.  Facebook   / n1education     / n1training   Instagram @N1.education @N1.training & @Coach_kassem Twitter @N1education