"When muscles are tense for long periods of time - [it] may trigger other reactions of the body and even promote stress-related disorders.
Both tension-type headache and migraine headache are associated with chronic muscle tension in the area of the shoulders, neck and head. Musculoskeletal pain in the low back and upper extremities has also been linked to stress, especially job stress.
For those who develop chronic pain conditions, stress-relieving activities have been shown to improve mood and daily function."