"1. If you are overweight, lose the weight. This is not training. It's just a prerequisite. Until you lose the weight, forget about training. If you're a man, get your body fat down below 20% (measured w/calipers etc., not BMI). Then you can start training."
"I am making it sound so convoluted; help me say it better."
I'll take a stab at it, Kat, by giving a couple exceptions to this statement whom I have personally hiked or climbed with.
1. Back in the 70's, I took 2 trips into the Upper Kern Basin, starting and ending at Road's End in KCNP, with a guy who had a grossly protruding pot belly and short stumpy legs. I can state with absolute certainty that his body fat was well north of 20%, with no need to resort to the calipers. We went in over Forester Pass both times, and exited over Harrison Pass on the first trip and over Thunder Pass/Longley Pass on the second trip. Both are fairly strenuous off trail routes, not to be taken lightly, as anybody here who has done either, or both, can confirm. We were both carrying over 50 pounds in our ignorance. This guy did just fine on both trips. His job as a furniture mover served as his training, and he was as strong as an ox.
2. I climbed, hiked, and backpacked for several years with another guy who reminded me of a well fed bear just before hibernation. His body fat was also well in excess of 20%, to the point where he was self conscious about it in the presence of a generally far leaner peer group. He was a solid 5.9 alpine climber of near legendary endurance and strength, served on SAR, and went on to run 16 ultra marathons,50 milers all, not fast, but he ran 'em nonetheless. Underneath all that flab was a lot of well conditioned muscle and a very strong cardio vascular system. We hiked the Enchantments Traverse 4 times, 2 in May in waist deep snow, and the last time in just under 7 hours from the Snow Creek parking lot, which adds an extra 1000' of elevation gain, the point being that this guy, fat and all, could haul a$$ in the mountains like very few I have ever come across, regardless of their body fat percentage.
Are these guys exceptions? Maybe, but I'd bet they are far from alone. Looks can be deceiving. So, to all you fat guys out there: If the idea of moving in the mountains gets your juices flowing, don't look in the mirror and flop back down on the couch. Get out there and do it. You might surprise yourselves. You've got nothing to lose but your flab. My 2 cents.