

The serratus anterior is an important muscle for scapular protraction and scapular upward rotation. At the same time, it is one of the most important scapular stabilizers and it is often underdeveloped.
To test the serratus anterior, the patient is standing and flexes the arm to 90°. The examiner then applies a backward force to the arm. With a weakened serratus anterior, one would find a winging scapula.
An alternative to test for serratus anterior strength is to have your patient perform a pushup against a wall or on the floor. Again, look for winging of the scapula when the movement is performed, which might indicate weakness of the serratus muscle.
If you are interested in muscle strength assessment of other muscles in the shoulder region, check out our wiki posts below:
Magee DJ. Orthopedic physical assessment-E-Book. Elsevier Health Sciences; 2014 Mar 25.