There are many more aspects that are not yet known or well understood scientifically, however. Some of the proposed theories are that massage:

• Might provide stimulation that may help block pain signals sent to the brain (the "gate control theory" of pain reduction).
• Might shift the patient's nervous system away from the sympathetic and toward the parasympathetic. The sympathetic nervous system helps mobilize the body for action. When a person is under stress, it produces the fight-or-flight response (the heart rate and breathing rate go up, for example; the blood vessels narrow; and muscles tighten). The parasympatheticnervous system creates what some call the "rest and digest" response (the heart rate and breathing rate slow down, for example; the blood vessels dilate; and activity increases in many parts of the digestive tract).
• Might stimulate the release of certain chemicals in the body, such as serotonin or endorphins.
• Might cause beneficial mechanical changes in the body--for example, by preventing fibrosis (the formation of scar-like tissue) or increasing the flow of lymph (a fluid that travels through the body's lymphatic system and carries cells that help fight disease).
• Might improve sleep, which has a role in pain and healing.
• Might provide some health benefit from the interaction between therapist and patient.

More well-designed studies are needed to understand and confirm these theories and other scientific aspects of massage.