Shoulder pain or shoulder injury can be caused by excessive mouse use, especially in people who are already experiencing shoulder injury, poor posture, muscle weakness in the upper back and neck muscles.
When typing at a computer keyboard that leaves your arm to hang beneath it for an extended period of time there are many health consequences that will surface over time for example Carpal Tunnel Syndrome if restrictions aren't made to actively stretch hands and wrists throughout sitting periods. Using a mouse during prolonged sitting periods also puts you at risk for dislocated shoulders brought on by fatigue-related muscular tightness in the upper extremities without avoiding simply repeated motions which cause compression of nerves to the Brachial.