Thanks for the feedback Phil, Nick, and Bareandagile. I'll try to address your comments and suggestions in aggregate for the most part.
I've been in superb aerobic condition before, while traveling through Africa, the Middle East and Europe on bicycle for two years, so I now know almost immediately when I'm getting out of the aerobic zone and building up lactic acid (if I remember my college biology correctly). That's basically what I mean by getting winded. It's a pace I can't sustain for very long. A friend gave me his old HR monitor last fall, and it simply confirmed what I already knew. According to the Mayo Clinic Max Heart Rate formula (which is higher than the Maf method) I consistently run and row in the proper aerobic range without thinking about it. The minute I exert beyond it, I know.
I'm also dubious about whether I'm ready to up the speed much at this point. Last November I jumped from five to ten miles and got a tiny stress fracture in my left foot. It didn't hurt too much, but it's only been since the beginning of March that it's been feeling completely fine again. So I'm building up more slowly this time. I stayed in the 2-3 mile range over the winter, more or less 3x a week, and then beginning in March, when all residual aching disappeared, began working my way up again. Yesterday I tried seven miles, but I started to feel it a bit in my metatarsals, and so ended up walking the last two miles in order not to risk re-injury. Today my feet feel fine, so I think I'll stay in the five-mile range for at least another few weeks. It's frustrating, but at my age (50), I'm beginning to learn patience. I'm almost a year into this latest chapter of the BFR experiment, although I have run barefoot before, in the late 80s, and have run shod before, for about two years at the turn of this century. During this last period I ran five miles 3x a week without any problems. Plus, I've been a barefooter by preference for most of my adult life, so I feel like my feet are in reasonable condition, but obviously they weren't ready for 10 miles back in November. It hasn't helped that I started out about 40-50 pounds overweight. I've already lost 25 pounds, and continue to lose about 2-3 pounds a month now that I've reestablished a good exercise regimen. And a lighter load will only help with the running. The virtuous cycle has been established.
I also used to be pretty fast, did well in the 400 and 800 the one year I went out for track, and played safety in football, so as Nick says, it would be great to feel my legs running with speed again. But I know sprinting puts even more stress on the foot, so I'm going to hold off on that until I can consistently run seven to ten miles in the seven-to-eight-minute-mile range.
Thanks Phil for your advice on interval training. Contemplating different running routines is new to me. Before I just ran a certain distance at whatever pace felt good and that was it. I did recently start doing hills a few weeks ago, and that feels pretty good, so I've been wondering about interval training too. It would be great to get some wind-sprints in once in a while too, but that's a ways off.
I appreciate B&A's advice for gait analysis, and luckily Johnny will be helping me out with that in a few weeks.
As for the knee-drive tip, it's at the 2:00 minute mark on Dr. Mark's video. Of course, it's just one aspect of his total analysis of good running technique, but it's the only one I've tried, and everything else seems to fall into place when I do that. Granted this is just my own naive, proprioceptive impression--only a veteran runner would be able to judge if I'm really doing it right. But it definitely feels good.
Thanks again fellas.