According to the Nanjing, an ancient acupuncture text, the region between the scapulas is considered to be associated with emotions.  Thus, the muscles in this area are commonly tightened, among individuals with chronic anxiety disorders as well as people who have been under chronic emotional stress. From a neuro-anatomical perspective, the area is also closely related to stress and anxiety conditions. http://www.acupuncturemoxibustion.com/acupuncture-points/anxiety-points/