Instead of assuming that the health bar represents the true limit of human endurance for injury and instead represents the limit of combat effectiveness, it would probably be something like this:
1 hp - minor scrapes, bruising and cuts. The only impact on effectiveness is a minor annoyance.
25 HP - Significant sprain, minor broken bones (single digit, rib etc. Mobility is notably impacted and pain is significant enough to provide a distraction in some tasks.
50 HP - Significant trauma - major broken bone (leg/arm), deep tissue cuts, bruising to organs. Mobility becomes difficult if not impossible as movement may cause futher injury. Pain is significant enough to cause a distraction in most acvitities. Significant medical aid is required for speedy recovery.
75 HP - Broken femur, significant gunshot injury. Mobility becomes all but impossible. Pain intense enough to cause a distraction in all activities. Medical aid required to keep injury from worsening and even in the best of care a person in such a state is going to take weeks if not months to recover.
99 HP - Significant wound to the head or upper torso, major internal bleeding. A person in this state poses almost no threat even when well armed and trained to the limit of human capability. Without medical aid death is all but certain. Recovery from such an injury even with medical aid is uncertain and likely going to be incomplete.
