Great question!
Shiatsu massage is not New Age; it is a Japanese healing treatment that applies manual pressure to specific points on the body believed to be energy pathways or meridians in order to reduce muscle tension, fatigue, and improve blood flow and the function of the lymphatic system. The word "shiatsu" actually means "finger pressure" because the fingers, thumbs, elbows and even knees are used to apply pressure during this type of massage.
It is said to have derived from an ancient form of Japanese massage known as Anma, and from acupuncture. Anma involves tapping, rubbing and applying pressure to different points on the body in order to stimulate the muscular and circulatory system. It's also used to return the body's "energy flow " to a normal state.
Tokujiro Namikoshi started the Japan Shiatsu college in 1940 where he integrated shiatsu with western anatomy and physiology. Marilyn Monroe was said to have been treated by him for an unknown illness which led to wider acceptance of the technique around the world.
In 1964, the Japanese government officially recognized it as a form of medical therapy.
A little more than a decade later, Shizuto Masunaga, a Japanese psychologist, created Zen Shiatsu which incorporates psychology, pressure points and neurology into the therapy and developed specific exercises for patients to perform to help reduce "energy" imbalances in their bodies. Zen Shiatsu is one of the more common forms of shiatsu massage in the U.S.
Although some practitioners of Shiatsu claim it can benefit a variety of physical, spiritual and mental ills, there is no evidence that it does anything more than what can be expected from a typical massage.