The stamina die

I just read on intwischa.com a really neat idea bout how to model fatigue. This does sound familiar, but I'm putting it up here for personal reference if nothing else.

On there they suggested everyone roll a stamina die when doing something that might exert your character, in addition to the regular die roll. When you roll a 1, you step down one die size and take -1 to all physical actions. Naturally someone fairly weak would start with a lower die, maybe d4, while someone more buff would maybe start with a d8.

I like  the simplicity of it all. Maybe you could even tie it into encumbrance somehow.