Just got back from a bike rid on Cougar Mtn. Where our apartment is the ride starts out as all down hill (we're pretty close to the top of the mountain). As I was descending...and descending...and descending some more I started doubting whether I could make it back up. So, a few hundred yards from the bottom I turned around and began the ride up.
I think I probably stopped about five times, on the verge of puking a few times. Part of the problem was going from coasting to full-on anaerobic exercise with nothing in between. The other part was that it's a long, steep climb with no breaks.
A couple times I actually contemplated calling Toni to come pick my ass up. But after a few breaks I finally made to the last half of the ride which consisted of some easy grades and a few small downhill sections.
I think I've definitely found a good measure for my fitness level as I begin to do more regular biking.