In many countries, PAP machines are only available by prescription. A sleep study at an accredited sleep lab is usually necessary before treatment can start. This is because the pressure settings on the PAP machine must be tailored to a patient's treatment needs.
The pectoralis major muscle also performs internal rotation -- turning your arm in toward your body. This action, also called medial rotation, is important for reaching behind your back to tuck in your shirt and combing your hair on the opposite side of your head.
Quick Answer. The principal function of the humerus is as a muscular insertion and origination point for a number of muscles, including the deltoid and pectoralis major. Since it is connected to the shoulder via a rotational joint, the humerus also supports the arm's various physical functions, such as lifting.