Yep! I can go all day out in Wyoming at about 6500'-7000' where we hunt with not even a day of acclamation. This year I went right out and tried to do some scouting for a guy at a little over 9200' and it whipped my butt real quick and I was sitting down every 100 yards. I went about 1 1/2 miles and went back to the truck and went down low! I couldn't believe how different that 2500' difference in elevation was. Oh, incidentally I'm 67 and in dang good shape for my age, but even at 31 you'll quickly find out what we're saying!