DEAR DOCTOR K: I have heard that tai chi can have a profound impact on the body and mind. What gives this exercise so much power? DEAR READER: Tai chi is a Chinese martial art made up of a series of graceful movements, one transitioning smoothly into the next. Tai chi is said to be good for both body and mind; in fact, it’s been called “meditation in motion.” My Harvard Medical School colleague Dr. Peter Wayne, with Mark Fuerst, has written an informative new book about tai chi called “The Harvard Medical School Guide to Tai Chi.” (You can learn more about this book at AskDoctorK.com.) Dr. Wayne discusses the “Eight Active Ingredients” of tai chi. He explains how, individually and in concert, they influence the body and mind. These active ingredients are: