More on pranayama

The overall length of the nerves in the body is about 6000 miles. Their functions being supremely delicate, extra care and attention are needed to keep them clean and clear. Repeated performance, with greater duration in each asana in many varieties, keeps the nervous system clean and clear, thus aiding the uninterrupted flow of energy (prana) while doing pranayama. 

B.K.S.Iyengar

(Btw, the above is an image of the pranic body, as visualised by the yogis -- a field of energy rather than solid)