I went hiking for two weeks on the Appalachian Trail last September and I thought I was in shape.  I ran pretty regularly before that and had built up some endurance.  Of course, it is Indiana and the flattest ground around, so I didn’t have experience hiking up mountains and I definitely didn’t practice hiking with a pak on my back!  So, word of advice, even if you run or workout, you most likely are not prepared for hiking.  I would definitely recommend hiking with some weight on your back and if you have access, up some inclines.  I definitely was in alot of pain because I hadn’t exercised the right muscles (including my back and shoulder muscled that carried most of the weight).  Just a thought to hopefully help everyone out- from my experience.  oh yes, and another word of advice, try to get a small and very light sleeping bag.  Mine was light and expensive, which was nice, but it was HUGE and caused quite a problem on the trail.