Studies of massage therapy are underway to understand what effects it has on patients and why. Some aspects of this are better understood than others. For example, it is known that:

When certain forces are applied to the muscles, changes occur in the muscles (although those changes are not clearly understood or agreed upon). Massage therapy typically enhances relaxation and reduces stress. Stress makes some diseases and conditions worse.

Many more aspects 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 parasympathetic nervous 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 benefits from the interaction between therapist and patient.