The shoulder is (or should be) the most mobile joint in your body. It's comprised of a complex system of big muscles (including the lats and pec major), smaller muscles (like the subscapularis, infraspinatus and deltoids), bones (humerus, clavicle and scapula) and loads of ligaments, tendons, fascia and other connective material. It's a highway for many important nerves (such as the Brachial Plexus), arteries and veins. The shoulder is awesome. And odds are if you work at a desk and have a mobile device you treat your shoulders like crap.