After getting in shape from walking with lead shot go to the next step that I always tell flatlanders to do before hunting the higher elevations and more than mole hill country. If you don't have a mountain to climb near you maybe there is a tall building where you can climb stairs. Start out slow and time yourself to the top floor, add weight to your pack every few days as you build your leg strength and lung capacity.
Years back I had a friend that lived at 50' above sea level come to hunt. He said he was in good shape as he ran 6 miles everyday. He could not keep up with this old geezer at 56 and he was 41. Then he understood what I meant about the high rise challenge.
