She's Z1 or low Z2, all the time. She is absolutely perfectly conditioned to do what she's doing, day after day after day. Send her to the Alps, and there's a 50/50 chance she'll blow up like a balloon with a grenade in it. She's climbed 109k feet in 47.5k miles-- that's 2.3ft/mi. I'm not a serious climber (over 200lbs and all) and I'm at 42ft/mi for the year 231k vertical feet in just 5,500 miles.