In real life, a heavy blow to the eyes impairs vision. A bone crushing blow to the feet, slows you down. The breaking of your arms makes working with them harder. This should be done in SMP as well. With damage regions, heavy Hits to the vital parts of your body should impair their performance.
They can be impaired like so.
Vision-
Reduce rendering distance, Or Decrease Alpha value on a screen filter.
They can be impaired like so.
Vision-
Reduce rendering distance, Or Decrease Alpha value on a screen filter.
Speed-
Decrease Mob Speed
Building-
Set a sleep interval for building.