Thoracic outlet syndrome is a nerve entrapment syndrome characterized by insufficient space for the passage of nerves between the base of the neck and the armpit (the thoracic outlet). It can be caused by the enlargement of the muscles surrounding the thoracic outlet, injury, weight gain, tumors, or poor posture.
Proper posture can alleviate the neck and shoulder pain associated with thoracic outlet syndrome, as can exercises to help relax the muscles around the thoracic outlet1.
1In one study of individual and work-related risk factors for neck pain among office workers, the 12-month prevalence of neck pain self-reported by 520 subjects was 45.5%. There was a significant association between neck pain and the habit of holding the neck in a forward, bent posture for a prolonged period of time.