Download Activity Analyzing the Pectoralis Major

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