Peer-reviewed medical research has shown that the benefits of massage therapies include pain relief and reduced trait anxiety and depression similar to the effects of psychotherapy. Massage also reduces blood pressure and heart rate. Additional testing has also shown reduced and improved recovery periods for muscle performance. Theories behind what massage might do include blocking nociception (gate control theory), activating the parasympathetic nervous system, which may stimulate the release of the ‘feel good’ hormones endorphin and serotonin. Massage therapy may also prevent fibrosis or scar tissue, increase the flow of lymphatic fluid, and improve sleep.