My wife and I are getting into running, and because we tend to have more friends older than us we are more aware of the anecdotal problems with running. Also, since we are both geeks and we research a lot there are a lot of interesting studies and discussions that make the simple feat of running more complicated.
This brings me to Knowing yourself as a Skill. I grew up with a weak constitution, despite being athletic as a kid. Where i'm weak is in disease resistance and various other alergies and nuances. I come to realize there are so many nuances to being me, I can organize and make a cheat sheet that would fill pages.
Then I realize where is it in my Character sheet where I know my limits? People don't normally know what their stats are unless they know some statistical benchmarks (to differentiate from anecdotal benchmarks) and have taken the time to measure against such and figure out all the assumptions and factors that should be inconsideration.
Like I'm tracking my Treadmill performance (because it is so damn polluted where I live) and consider it Ideal, and going by my wife Tread mill to Jogging around our area to 30% diminished performance. You have to do it before you know how much you can do, and you have to be careful not to injure yourself. Now that I'm going to take running as a crosstraining for my airsoft I realized I have to get a sports medicine check up if all the parts are working as it should.... how often do characters know what is really going on in their body... only the GM knows.
Since I found out in a random office test that i have Hepa B (a disease I was supposed to be vaccinated against) I am acutely aware I don't know squat whats going on in my body. Its only with age am I more hyperaware of pain and carefully documenting my conditions that I'm able to see patterns and learn from mistakes.
Its even worse in a non-scientifically literate environment like mine, where many horror stories are people who just started running without a checkup and consideration of their family's medical history losing kneecaps and having a heart attack.
I consider myself lucky so far, when I was younger I would push myself to breaking playing while having shin splints. That was stupid, but not as stupid as diving into concrete for a soccer game and having a very bad wound that didn't heal good as new.
What I'm getting at is that, even your body needs gaming. I can't advance my health level until I get a medical check up and build a strategy with the limitations with the doctors' help. Seeing my father who is in his 60s slowly shrink should really emphasize how damn fragile bones are and how I should be taking better care of them if I want to be an ass kicking old man.
Funny that there is no skill for that in GURPS or in any system, which is ok. Although I do have a feeling "personal health" will be a skill eventually, when there are better ways of tracking our patterns and using hard data versus anecdotal information. Its going to be one of those skills that may be essential like basic science, being able to fill taxes and bureaucratic forms, research, ethics, and practical economics.