Fun & Fitness over 50

As I mentioned, I started doing intervals a la Sally Edwards recommendation in my heart monitor booklet; 10/5/5 x 3, i.e. three sets of 10 minutes @ 50-70%MHR, 5 min @ 70-80 and 5 min @80-100. What I'm actually trying to do is 10 in the 60-70% range, for the 1st interval, that is, zone 2.
I'm really liking this workout. The first set is hard but after that I'm warmed up and diggin' it. I've got a good cruisin' level for the Pzone (80-100%) interval @ about 150bpm, that's 85% MHR for me. Felt really great after this workout. I go out to a flat, quiet farm road (Mead's Lane for you locals) with no intersections and just go back and forth on it for my workout.
The only problem I had was on my way back home after I finished. My chain came off the small cog when I started pedaling up a steep hill. Have to adjust the high limiter tonight after work.
Less than 2 weeks till the Tour de Cure!