Or Lotus posture (Guru Dev sits in this posture) keeps the spine erect like an archers bow to ensure proper flow of vital pranas upwards.
All orthopedic doctors recommend a small pillow at the small of the back to accomplish this, short of this, poor posture over many years causes bone spurs in the neck and spine, especially if you are falling asleep while meditating (terrible posture, leading to early onset of arthritis). Notice the sloppy posture of even John Hagelin when he meditates, note how his neck falls when he is seen meditating, over the years he will pay a price for that, too bad MMY didn't establish proper guidelines for correct posture for meditation before he died. Meditation isn't sleep!! MMY doesn't stress the importance of this posture because TM is Yoga-lite for modernity! When a meditator consciously transcends he is purportedly able to maintain constant perfect posture! even in the transcendent state! Wiki on the Lotus posture below: http://en.wikipedia.org/wiki/Asanas
