Final answer:
The supraspinatus is the most frequently injured rotator cuff muscle, prone to injury from repetitive overhead activities and can become pinched or torn.
Step-by-step explanation:
The most frequently injured rotator cuff muscle is the supraspinatus. This muscle is part of the rotator cuff, which also includes the infraspinatus, teres minor, and subscapularis. Each of these muscles plays a crucial role in the mobility and stability of the shoulder joint. The supraspinatus muscle, located superior to the spine of the scapula, is particularly susceptible to injury due to its position in the shoulder mechanism and the stress placed on it during overhead activities. In many shoulder-related injuries, such as those experienced by baseball pitchers, the supraspinatus tendon can become pinched, inflamed, or even tear away from the bone.