Success...

30 minutes, 6 miles an hour... two days in a row. My legs ache, but none of the troublesome signs that were plaguing me before during exercise, with one exception: I had the mildest twinges of a headache while exercising. I took aspirin before starting (better to get ahead of the headache than to fall behind it) just in case, and if a headache was trying to sneak up on me, it seems to have sneaked away for now.