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.
Because of where the levator muscle attaches to the shoulder blade/scapula, when the shoulder blade is rotated upward, the attachment of the levator moves downward, away from its other attachment to the neck. Try it out!