Final answer:
The posterior shoulder ball roll primarily targets the rotator cuff muscles, which are crucial for shoulder stability and movement, but may also engage secondary muscles like the deltoid and trapezius.
Step-by-step explanation:
When your client performs the posterior shoulder ball roll, the primary muscles targeted are the rotator cuff muscles, which are essential for the stability and movement of the shoulder joint. These muscles, including the supraspinatus, infraspinatus, teres minor, and subscapularis, arise from the scapula and attach to the greater or lesser tubercles of the humerus.
The exercise helps in strengthening these muscles, which work as a cohesive unit to stabilize the shoulder and perform various arm movements. It enhances the dynamic ligament role of the rotator cuff, which provides the primary structural support for the glenohumeral joint. Secondary muscles involved may include the deltoid and trapezius, depending on the variation and intensity of the exercise.