College of Massage Therapists of British Columbia (CMTBC) Practice Exam

Which muscle might be shortened when active range of motion testing shows decreased internal rotation of the humerus?

1. Teres major

2. Infraspinatus

3. Subscapularis

4. Latissimus dorsi

The correct answer is: Infraspinatus

When active range of motion testing indicates decreased internal rotation of the humerus, the muscle that is most likely to be shortened is the infraspinatus. The infraspinatus is a part of the rotator cuff muscle group and primarily functions as an external rotator of the shoulder. If internal rotation is limited, it suggests that the external rotators, including the infraspinatus, may be overactive or shortened, contributing to the restriction. Conversely, the muscles that are responsible for internal rotation, such as the subscapularis, teres major, and latissimus dorsi, may not be shortened in this scenario and typically assist with that movement. Understanding the role of the infraspinatus, it's clear that by being tight or overactive, it can counteract the function of the internal rotators, leading to decreased internal rotation during movement testing. This highlights the importance of assessing and addressing muscle imbalances when evaluating shoulder mobility.