Activity – Analyzing the Posterior Deltoid
In this activity we will use the "3 Rules of Muscles" to determine the joint actions of the
posterior deltoid. Answer the questions below:

Hints in Blue
Shoulder (Glenohumeral) Joint Actions Word Bank
Action
Plane
Flexion
Extension
Abduction
Adduction
Horizontal Abduction
Horizontal Adduction
Internal Rotation
External Rotation
Sagittal
Sagittal
Frontal
Frontal
Transverse
Transverse
Transverse
Transverse
© 2014 Brent Brookbush
1. What direction (plane) do the fibers of posterior deltoid run?
2. In what plane/planes do you think this muscle will function best?
3. When this muscle shortens which direction will it pull the arm?
4. What is the name of the joint action that occurs in that same direction?
5. What happens when you raise your arm to the side by 90 degrees (elbow level with
shoulder)? In what plane are the fibers aligned?
6. Now, which direction will the posterior deltoid pull the arm, and what is this joint action
called?
7. Generally muscles that rap around a bone, and those that have an obliquity (run diagonally)
will contribute to rotation. Which direction will the posterior deltoid rotate the arm?
© 2014 Brent Brookbush
8. Re-write your answers into one succinct table?
Posterior Deltoid
o Joint it crosses:
o Actions:
9. What is the relationship between the joint actions of the posterior deltoid and the anterior
deltoid?
Check your answers
© 2014 Brent Brookbush