17 sections: https://pzwiki.net/wiki/Health

1 section for entire body https://pzwiki.net/wiki/Endurance

This seems wrong - if I'm climbing a bunch of stairs my legs will get tired but my arms would be fresh. If I'm using my right arm a bunch but resting my left, my right should get too tired to fight well buy my left should be fine if I swap the weapon to the other hand.

This seems like it would be a really interesting thing to explore in a mod, not sure if anyone has yet. Think about how it might make combat more interesting - you'd vary techniques - maybe start kicking zombies a bit to let the lactic acid clear from your arms before swinging the crowbar again.

Yeah there should be a systemic endurance too - all body part fatigue would sap energy from your central fatigue, but there should be a localized fatigue system too, and local fatigue shoudl emulate some effects of injury (being less able to use a body part) but you recover from it faster than you would an injury.

In some cases local fatigue should risk injury too, tired muscles can tear more easily, etc.