I think many of them are capable of it to some degree. I spent the summer doing field work in Utah and the slopes and heat could be punishing for 6+ hours a day, 5 days a week. But a few in my group were overweight, one was probably 250, another was likely around 300 lbs. But they made it up every mountain. Sure they were at the back and sweating profusely,  but they made it. To me the saddest part is that they don't WANT to move. My mother won't even go on a walk around the block on a 70 degree day, and she's supposedly "pagan" and "loves nature"