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Activity – Analyzing the Pectoralis Major In this activity we will use the "3 Rules of Muscles" to determine the joint actions of the pectoralis major. In the lessons that follow we will use these same rules to build a conceptual understanding of functional anatomy - moving us beyond "rote memorization" and onto analysis, synthesis and evaluation. It is important that you take the time to understand this activity and not jump to the answer key! Answer the questions below Hints in Blue Illustration of Pectoralis Major - http://www.natashahayden.ca/wp-content/uploads/2014/06/pectoralis-major.jpg © 2014 Brent Brookbush 1. What joint does the pectoralis major cross? Shoulder (Glenohumeral Joint) 2. What joint actions is that joint capable of (Make a word bank for yourself)? Flexion Horizontal Adduction Extension Horizontal Abduction Adduction Internal Rotation Abduction External Rotation 3. What direction (Plane) do most of the fibers of the pectoralis major run? Transverse 4. Highlight the joint actions that occur in that plane (Does that narrow down your choices?)? Flexion Horizontal Adduction Extension Horizontal Abduction Adduction Internal Rotation Abduction External Rotation 5. When the muscle shortens which directions will it pull the arm? (If you are having a hard time with this step consider your favorite chest exercise?) “Forward and In” 6. What is the name of the joint action (highlighted above) that occurs in that same direction? Horizontal Adduction and Internal Rotation 7. What if you raised the arm to 90° of abduction (Repeat steps 3,5 &6)? 3. Transverse and Frontal (sternal head) 5. Forward and Down (sternal head) 6. Horizontal Adduction and Adduction © 2014 Brent Brookbush 8. Do you think the pectoralis major may contribute to any other joint actions? The clavicular head of the pectoralis major runs almost parallel to the anterior deltoid. The anterior deltoid is great at flexion and I could see the pec “assisting” in this motion. 9. Re-write your answers into one succinct table Pectoralis Major O: Medial half of clavicle, sternum and costal cartilages I: Intertubercular groove of humerus Actions: Horizontal Adduction (prime mover) Internal Rotation o o Clavicular Head: will assist in shoulder flexion Sternal Head will assist in shoulder adduction © 2014 Brent Brookbush