What substitutions occur during shoulder external rotation MMT?

• A. Trunk rotation and/or scapular movement, or elbow motion compensating to reduce rotation
• B. Elbow flexion
• C. Wrist deviation
• D. Ankle instability

Answer: (A)

Substitutions in manual muscle testing are when other parts of the body take over to accomplish the movement, masking weakness in the target muscles. For shoulder external rotation, the body often recruits movements outside the glenohumeral joint to produce the rotation. Turning the trunk or allowing the scapula to move can rotate the shoulder girdle as a unit, giving external rotation without true isolated external rotation at the shoulder. The elbow can also change position (for example, through elbow motion that changes forearm orientation or engages the biceps/supinators) to aid the rotation, acting as a substitute for the targeted external rotator muscles. These substitutions are common when the external rotators are weak or stabilization is insufficient.

Wrist deviation and ankle instability aren’t typical substitutes for this motion, and elbow flexion alone doesn’t capture the common compensatory pathways seen during this specific test.