A balanced posture generates alert awareness

A balanced posture requires very little effort to sustain and allows the major muscles of the body to relax. This relatively small expenditure of energy, coupled with the phenomenon of relaxation, produces a distinct feeling tone of softness, ease, and vibratory flow. It also generates a natural condition of alert awareness. This dual condition of comfort in the body and relaxed alertness in the mind is the fruit of balance.

Will Johnson in "The posture of Meditation" page 20