1: Extremely frail. Reacts violently to anything foreign in the body, very brittle skeleton, and likely unable to stand without self-injury. Often applies to infants and dying characters.
2: Very frail. Barely functioning immune system, often has severe bodily injuries from what would be minor damage to the average person. Needs extensive medication to live normally. Often applies to severely injured or dangerously ill characters.
3: Frail. Low-functioning immune system, and will be left bedridden from minor disease. Fragile limbs and suffers extreme pain when damaged. Cannot sprint for longer than a dash. Often applies to stunted or injured characters.
4: Functionally frail. Weak immune system, affected by disease more often and more violently than the average person, but managed reasonably well without medication. Slightly fragile skeleton, may be inflicted with great pain from lighter attacks. Often applies to children and those with underlying physical issues.
5: Average endurance. Average immune system, sometimes afflicted by sickness but can often overcome without help. Can easily withstand minor bodily damage, and major damage given time to heal or medication. Severe damage such as gunshot wounds will immediately incapacitate. Can perform reasonable labor without being too tired out. Often applies to average workers or service personnel.
6: Durable. Well oiled immune system, not often afflicted by major disease, and handles it well when it does happen. Can withstand major damage without much trouble, given time to heal later. Severe damage will not incapacitate immediately, but will prove fatal if left untreated. Extreme damage will kill immediately. Can perform a lot of labor in a day, and not easily winded. Often applies to wasteland wanderers, recruit soldiers, and traveling merchants.
7: Very durable. Very sturdy immune system, can shrug off mild sickness and keep going strong. Can withstand major damage without help, and severe damage given time to heal. Extreme damage will incapacitate immediately. Can run marathons without unbearable physical strain, and doesn't need much rest to recover from damage. Often applies to veteran wastelanders and elite soldiers.
8: Incredibly durable. Powerful immune system, and can passively recover even from major illness while in the wastes. Can withstand severe damage without much pain, and can survive extreme damage with time to recover afterward. Rarely feels too tired to keep going. Often applies to expert survivalists, veteran rangers, and revered soldiers.
9: Extremely durable. Virtually unmatched immune system, rarely afflicted by the most deadly sicknesses and has great odds of survival if they are. Can withstand extreme damage and continue fighting, albeit suffering pain unimaginable to the average body. Practically impossible to tire. Often applies to storied survivalists, only the most hardened elite soldiers, and those who have suffered pain unimaginable and managed to survive only by their own grit.
10: Inhumanly durable. Untouched by illness, and suffers none if afflicted. Can withstand extreme damage without a scratch. Probably well known for deflecting .50 BMGs with their abs. Never feels tired unless being in extreme stress for days, and rarely feels pain that is not bearable. Only applies to truly legendary individuals, as no amount of dedication could lead to such feats besides otherworldly blessings.