There is little to tell. Basic Training has more to do with getting used to being miserable than actually pushing yourself. The actual job training is somewhat more challenging, but only because there is very little room for error. You aren't allowed to bring stuff home to study either, so there's little extra you could do even if you wanted to.

I did force myself up and down 800-some steps (as in a staircase sort of thing) while wearing about 90 lbs (I weigh 140) of gear, but that was completely voluntary. It was excruciating, but I recognized that quitting would have to be a conscious choice not to take another step, so I just didn't do that. I did stop before I had properly finished, but that was only because my legs were about to stop supporting me. It shouldn't be that hard to find an exercise program that gives a similar effect, without being anywhere nearly as bad for your body.

The biggest thing I learned is that you have a choice about your attitude. When doing sucky things, I've noticed that there are two main ways that people do it. They either complain, or they laugh at the people who are complaining. Either way, you're miserable, but at least the second group has something to laugh about.

Sorry that kind of rambled. I hope I answered the question to your satisfaction.