Myofascial pain trigger points from infraspinatus are some of the worst I’ve ever seen in bodywork practice. Having had problems with the area myself, clients aren’t usually very happy when I find problems with theirs. It’s one of the most painful things I’ll work on anyone.
Infraspinatus helps control rotation of the head of the humerus or upper arm. It’s part of the rotator cuff that reaches around the shoulder joint. Releasing this area gives someone a much wider range of motion in the shoulder joint and if you have arm or shoulder pain I highly recommend trying this to see if it helps.