Gas expands, volume increases (surface area increases) as P = F/A. Clearly force also needs to increase to keep P constant. A greater force means a greater rate of change of momentum, so the molecules must have a greater mean kinetic energy. Therefore the gas must be at a higher temperature meaning heat energy (Q) must be supplied.
When the shoulder is shrugged, this muscle is at work. When a heavy bag is carried, the levator scapulae muscle helps the body bear the burden. This muscle begins at the vertebrae just below the skull, called the cervical vertebrae. It is attached to the transverse processes of the cervical vertebrae.
A rotator cuff is comprised of four muscles (supraspinatus, infraspinatus, subscapularis, and teres minor) located in the shoulder area, which provide support to the shoulder joints. Any kind of rotator cuff injury, such as a subscapularis tear, can result in scapular pain.