Its not even something hard to come up with if you are active, understand you body and generally how workouts work on you.

I've trained in similar fashion for my trip to Aconcagua or Nepal, and never researched for that nor discussed with anybody. You carry big backpacks up there a lot, or smaller backpacks for 10-12h each day, every day in places where lack of oxygen makes you lose breath in 5-10 steps easily when walking uphill. It figures that when training for strength-endurance there needs to be a lot of repetitions with some added weight.

I just took some weights into backpack at building I was living back then, hiked those 8 floors on stairs, took elevator down, rinse and repeat many times. Or elliptic trainer with same backpack. Or other movements/machines (just don't run with that).