The three-minute runs are still hard work. About halfway through, I wasn't the least bit convinced that I was ready to move on to week four, so I decided to try an experiment. Can I run five minutes without stopping?
The scheduled run was 90s run, 90s walk, 3min run, 3min walk, then repeat. Ms. Overachiever decided that she was going to try to do a 5min run as the last one, rather than a 3min. If she succeeded she'd move on to week four. If not, she'd do remedial week three.
Guess what? I can run five minutes without stopping. I probably could have done more, but I'm not crazy. (Well, maybe.) The three-minute run gets to "this is annoyingly hard", but it doesn't seem to get much worse if I keep going beyond that.
I also decided to pay a lot of attention to my heart rate, in particular how long it takes for me to recover from a run. I know what my baseline walking-at-a-moderate-pace heart rate is, and what I hit at the end of a running segment. It takes me about 60 seconds to recover from a 90-second run, and about two minutes to recover from a three-minute run. That last one is interesting (to me, at least) because week four starts with a three-minute run followed by a 90-second walk. I think I'll be OK, though.