Great question — answering as the UphillTech team:
Aerobic conditioning will help a little with the altitude. You can practice walking / running on a treadmill at 15% incline. You can practice walking with a loaded backpack. Bonus points for doing it on an inclined treadmill.
Full answer by xpda: https://outdoors.stackexchange.com/a/472 (CC BY-SA 4.0).
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