Uphill fast-walk intervals  - I know, kinda lame, but this is what I did:  8 x 1/10 mile uphill (15% average grade) fast walk on Cowles Mountain with a walk back down between each.  I averaged 91 seconds with an average heart rate of 143. My highest observed heart rate was 168 - I don't know if it can go much higher anymore. My body weight is 180, my trail weight today was 183. Why intervals? To begin preparation for hopefully running in a few months. I don't plan to run "much" (per doctor's instructions) if and when I am able to run again, so I'd pack as much as I can into relatively few miles per week, including  - intervals! I'll try actual running after waiting the prescribed 6 months after surgery as long as my body feels ready. To reduce the stress on my joints, I have also decided that I won't run until my weight is under 160. I'm at 180 now, so that could take a while. If I never get there, I guess I'm not very motivated to run.