Answer C) Infraspinatus
Overhead throwing activities (e.g., baseball pitching) place supraphysiological loads on the tendons of the rotator cuff.
Through eccentric contraction, this type of activity especially strains the posterior rotator cuff when slowing down after releasing the ball.
Tendon overload can cause microscopic tears called micro injuries.
The relatively avascular nature of tendons means that these micro injuries have limited healing potential and can propagate into partial or full-thickness tears, or tendinopathy.
The infraspinatus muscle, along with the teres minor muscle, is responsible for the external rotation of the humerus. This patient’s shoulder pain during external rotation suggests infraspinatus tendinopathy.