Fit to survive, hmm, how can I elaborate.

I work with a short, skinny mexican. He also hits the gym with me every day. He is in pretty good shape, lean, quick, slightly muscular. He's maybe 5' 6" tall. I am 6' 6", weigh 250, and have a nice pooch hanging around my bellybutton. Two things about this contrast to note.

1. All things being equal, he will outlive me in the natural course of events. It is for the same reason that Chihuahuas last longer than Great Danes. You will not see many basketball players in their 80s.

2. When I work out, I can easily expend 600 calories in half an hour. He struggles to get to 500. I can go for maybe 2 hours without a break on the elliptical, he is gassed out after 45 minutes. My BMI is probably twice what his is, but that is intentional.

I don't think being real thin and having a low BMI is the key. I think staying reasonably active, knowing your limitations, and pacing yourself are the real solution. It used to be that when I was younger, my friends said I moved through the forest like an elk. I could go all day and cover 20 miles, or I could run through the brush just about as fast as I could run down the track in a 100 yard dash. I was never the fastest kid in track, and I couldn't run for miles and miles, but I could set the autopilot and cruise and get from point a to point b pretty darned well.

I have slowed down with time. All of us will. Who wants to live forever? The point is now I don't have to try and run 10 miles to survive, I have to think where is the nearest best place to get to to survive, what do I need to take with me, and how long do I need to be there for? If I had to try and run to the next nearest Army base, I wouldn't make it. Guess what, neither would anyone else. If I had to fight hand to hand a bunch of insurgents, I would lose. So would anyone else, it won't matter if you were Steven Seagal or Bruce Lee, you will eventually reach your limits.

Consider this, when Lewis and Clark reached the Pacific, the men needed to consume 8 to 10 lbs of meat a day just to maintain their weight. These were not fat men! I have eaten up to 40 ounces of prime beef at one sitting, not having to consume anything else but water. It can be done, but it is a chore. Can you imagine how much work they must've been doing to maintain that burn rate? There's a reason people carried big balls of fat around with them back then (they called it pemmican). They needed that much energy just to survive.

If I were in a real survival situation, I can imagine burning 10,000 Kcal a day. I reckon the first few days would be killer. I am not in the kind of shape to burn that many calories a day comfortably. But I think I can still attain that level if I had to.

My conclusion is that a little sense can save you a lot of effort (sounds like what Chris said). Fitness is probably secondary to knowing how to use the limited resource your body can provide to greatest benefit. Still it is kinda like letting your gear sit around and collect dust. You gotta take care of your assets if you expect them to be any good when they are most needed.