In my opinion, the best way to train for the mountains is the mountains.

Don't get me wrong, cardio is a great idea for many other reasons, and it DOES help to get up Whitney. But there are things that cardio won't prepare you for, which will drain your energy just as easily. Like carrying a backpack, or handling temperature changes, or sleeping on the hard ground in a sleeping bag. The mode of energy expenditure when hiking uphill at 12000' is not quite the same as running on a treadmill or climbing a stairmaster.

I wish I had the wherewithal to do 6 hours/week of cardio in the gym like you guys. I just don't. I consider it a personal achievement if I can manage two hours a week. But I've been on four 12-hour hikes above 10,000' since July. Last time I made it to the cables and back in one day. It seems easier every time.