I've got something similar. Six levels: Hale, Winded, Tired, Weary, Spent, Exhausted.
Assuming Hale, at the end of combat or other exertion roll Con x5 - Enc. You make it, you are still Hale, if not you drop to Winded, which imposes a -5% on skill rolls. Roll at Winded is Con x4 - Enc. Make it, stay Winded, don't then you fall to Tired which is -10% to rolls. And on... each level going down one Con multiple and doubling the skill roll penalty from the level before.
I hadn't thought about adding a Mov penalty, but might at the higher levels.
SDLeary