The infraspinatus is a thick triangular muscle that starts in the upper back on the shoulder blade (just a little below the supraspinatus), and connects to the back of the humerus. Like all of the rotator cuff muscles, the infraspinatus helps to hold your humerus in place and keeps your arm stable.
The main function of the infraspinatus is to externally rotate the humerus and stabilize the shoulder joint. It is the main muscle responsible for external rotation (although next months muscle does assist as well). And, as alluded to last month, the infraspinatus does assist in both abduction and adduction. A recurring theme you will see with the rotator cuff muscles is that while they each have their primary function, to some degree they do assist with the other rotator cuff muscle’s actions. Since the rotator cuff muscles are responsible for shoulder stability, this makes sense.
The infraspinatus is strengthened using one of the most common rotator cuff exercises you’ll see: external rotation with a band. However, any number of external rotation exercises, with or without bands, will help to target this muscle. If you are looking to stretch the infraspinatus, the sleeper stretch is a great option.