The infrapinatus muscle is a small, triangular muscle located in the posterior aspect of the shoulder. It is one of the main muscles responsible for external rotation of the shoulder joint, and is important for activities such as throwing, reaching, and lifting objects. The infrapinatus muscle originates at the scapula, or shoulder blade, and then inserts at the greater tubercle of the humerus, a bony landmark on the upper arm bone.

The infrapinatus muscle is one of the primary muscles responsible for externally rotating the shoulder joint. This movement is important for activities such as throwing, reaching, and lifting objects, as it allows the arm to move away from the body and outwards in space. The infrapinatus muscle also plays a role in providing stability to the shoulder joint, which is important for preventing falls and protecting the shoulder from injury.

In terms of daily uses, the infrapinatus muscle is active whenever we reach, lift, or perform any other activity that involves external rotation of the shoulder joint. It is also used when we climb stairs, rise from a seated position, or perform movements that require stability of the shoulder joint, such as standing on one leg or performing single-leg exercises.