In my 40's, I had lived in Florida for most of my life. I could not seem to get in the right shape for mountain hunting no matter what I did. With my workouts (bike riding, walking, and climbing stairs), I could always walk anyone from the east into the ground but sucked compared to the locals who lived at altitude. I got the bright idea to do some blood packing and asked my internist for his opinion. Ended up having my doctor save up drawn blood and putting it back the day before I left for a hunt. It helped out a lot. Eventually, I moved to Montana and now live at 4,000 ft on the side of a mountain. This worked a lot better.