Thanks, you two. I actually have the Carmichael book The Ultimate Ride, and he describes doing 2 x 8 minute (or 3 mile) efforts and taking the average of those two...using that rather than actual max HR. I did that one a year or two ago, and I always wondered if I was using a high enough number for setting my zones.

I mention the gasping part because I seem to have a tough time, either on the trainer or in spin class, pushing myself to what I think my actual max might be. Whereas when I am out on the bike on a really hard, steep hill, it is all I can do to keep from falling over and it seems like my lungs will just burst if I keep trying to get more air in.

I'm feeling very insecure about my HRs and setting the zones. Sometimes I feel like I'm working too hard for a given workout, and others I doubt that I'm working hard enough.

Thanks for your help.