Effort at altitude will always leave you breathless.
A week ago yesterday, I summitted a mountain at 19,300 feet (not on a bike, of course!) and no matter how many deep breaths I drew, I couldn't get the oxygen my system desperately needed. I learned more about altitude than I ever wanted to know!
Pictures / blog here:
https://picasaweb.google.com/1103015...eat=directlink