My understanding is follows:
Your max weight plane has a Va of Xias. Flying at that speed and weight, the difference between your alpha and the alpha to stall the wing is less than can be commanded by full up elevator. As your weight goes down with burned fuel, the same lift requires less alpha, therefore the margin expands. So, unless Va is consciously and correctly reduced by the pilot, he can damage the plane with sudden, full up elevator.
I'm choosing up elevator just as one example of a control input.
I'm sure one can get much more specific and wrapped up in symbols if one likes.