The arms join the body at the shoulder, obviously. This is the highest point of the arm, and means that gravity is always extending the arm down its length towards the hand. Tense shoulders represent our fearful attempt to hold onto our arms and keep control of our hands. If we really relax the shoulders then we have to use the turning waist to direct the hands, turns which either throw the hands out from the body, or fold them in from the elbow. Taiji, to start with anyway, is simply the study and practice of directing relaxed arms with the waist; an operation that requires a root otherwise the waist has no power.