blindsage
Master of Arts
He probably means tucking the tail bone under and the tilting of the pelvis.
The theory being that incoming force will be better transfered through the arms , down through the spine that is straight-ish and finally absorbed by the stance.
You would think that's what he meant, but what he said was:
Sorry but you are wrong, Stance training actully DOES straighten the back, It removes the curve from our lower back,
Its a mental path to achieveing it but Its no imaginery thing,
SNT
LOL. Methinks you need some basic anatomy training.