For lack of anything better right now Im going to call it an adrenaline boost. When a nade comes at you, satchel, or any imminent death you should be able to sprint away for a short time regardless of your stamina bar. The game should somehow recognize this imminent threat and let you dodge the danger with a boost of energy. Theres no way you would see a nade at your feet and say "oh damn, too tired to run away, cant do it, oh well" and then blow up. No matter how tired you are you'll get the hell out of dodge.