" The waist must be sunk if it is to be the master of the body. It is necessary to have a root in the foot so one can pass the energy up the legs and into the fingers by means of the waist. A loose waist links upper and lower body naturally so they move in co-ordination. This co-ordination is vital if one is to use the body as one unit, relying on internal energy rather than external muscular force to execute the commands of the mind. This relaxation is brought about by use of the mind to begin with and then naturally."
B.T.C.C.A. Handbook for the 2nd Term.