Rob,
I can see what you're talking about, but I also see the other sides of the argument as well. I know that PERSONAL DRIVE is often times far more important than just about anything, and if you're not MOTIVATED to do whatever, you're not going to be able or put forth the energy to do it. In all honesty, the 10,000ft altitude kicks ALL OUR SEA LEVEL butts for the first few days, there ain't no way around it, but if you keep driving on, I believe you adapt better. Hydration is certainly a VERY important factor as well, as is proper nutrition to include electrolytes and such. I've always had good "farm strength" and endurance, as I was raised working, cutting wood, splitting wood, working around the house, working for my dad's construction company, etc. My lungs are my biggest set-back, and I can do moderate exercise almost "endlessly" but in those mountains, where the air is thin, I tire much easier as my body is deprived of the oxygen.

Now when talking about HR's etc, many of those long distance bikers, triathletes, marathon runners, etc, may only be having a HR around 120-150 when they are running, biking, swimming, whatever, but when you consider their baseline HR's are only in the 30's in MANY cases, 120-150 is HIGH, like 200+ for a person in "decent" shape. And heavy workouts repeatedly certainly deplete muscles, and don't allow proper time for restoration as well, that is part of why many guys will lose 10-15# during their 7-10day elk hunts, because they are working their bodies out int a "BIG" way, also probably getting "anaerobic" workout much earlier than at sea level since the oxygen supply is so much lower. I know I lost about 10#, and came home RIPPED from my last trip out, but in short order....2 months, I found all of those pounds back. Likewise, I'll probably drop 10-15# this time out, and in some ways, I believe having a little extra fat on the body is a little bit of an advantage as a fall back energy source. Especially for heavy lifting hauling, etc. At this point, I'm working out a busted ankle, so I'm in the air about my date if things are in better shape within the next 2 weeks, but I took an air cast into the mountains with me in '05 as well recovering from the worst grade sprain you can possibly get, and spending almost 5 months from Nov. - April in an immobilizer boot, I was fine, I just have a little less time to get it together this time, but also a little less damage to heal up.