What the Pec?! By Michele Cook|2023-09-27T21:43:01-04:00May 24th, 2022|Categories: Muscles|Tags: pec, rounded shoulders, shirt hurts| The Pectoralis (Pec) The pectoralis aka. pec major is a large muscle covering the chest from the clavicle to the abdomen and inserts at the top of the arm (the humerus). It is responsible for actions like push-ups, also Read More Comments Off on What the Pec?!