My permanent address is at 6500 feet. My temporary one is at sea level.

When I go back home, I have to acclimate for a couple of days. The rule of thumb is one day at altitude above 3000 feet. So for me, three days and I'm usually fine. But I can ride after two days, I don't need three.

If you are riding 'casually' on flat stuff, it's not bad, but if you are going to start climbing and really mountain biking (not sure if you were doing that or road biking), then try and take it easy the first day, then the second day do a little harder ride and the third day maybe work at 75%. After that you'll notice it getting better.

Like someone else said, drink up. You dehydrate alot quicker as the humidity is usually alot lower and you'll be panting alot more which will work against you as well.

And if you feel crappy (headache, pukey, dizzy), stop and try and get to a lower altitude if possible. You may not feel much at 6,000 to 7,000 but you will feel it at 8,000-9,000. Just go slow. No reason to wind up feeling crappy!

Don't drink alot of alcohol either. That will work against you as well, not to mention dehydrate you.

Oh yeah, and have fun!!!!