My story is basically the same. Got rejected at the draft due to a back
problem. The doctor was asking
if I wasnt experiencing lower back pain, which I never did until he asked
me. I was a fairly active runner
and triathlete for more than 15 years after that without problems and my
doctor said that the extra weight training that we did was compensating.

Most doctors claim that doing what you describe is one of the best ways to
reduce backpain in general.