Ohhh I read about it once (after having seen some pics of Franck Zane sucking in his tummy to the ribs!!) and if I remember right then it's all a question about practise. Lie flat on the floor and concentrate about your respiration. Now inhale deeply and then exhale sloowly until you cannot any longer, then stop for a while, exhale a little again, stop and then inhale. Restart this.
-------------- - Nina :o) Les Victoires éternelles sont celles du coeur.