94. Swami Vishnudevananda
"Flexibility of the body--especially of the spinal column -- and flexibility of the mind are interrelated. Flexibility of the mind means adaptability. Its opposite, rigidity of the mind, is called ego. And as ego puts stress upon the nervous system, it creates a rigid body. For a spiritual aspirant especially, flexibility is necessary. Once the prana starts flowing, any resistance will prevent its free movement, so every morning you should practice your asanas, pranayama, and mantra japa. Flexibility of the spinal column will allow the energy to flow properly; instead of going downward, it will go upward. It is just like water, which, in a gross state, flows downwards, but when in subtle form (as in steam) it rises. In the same way, a flexible spinal cord will allow your energy to flow upward, past the lower centres and up to the higher centers. That is what is meant by 'the ascent of kundalini Shakti'."