"Well", you are correct in that my walks between whatever I was doing became shorter as my body accepted the work I was doing. Therefore my heart-rate stayed high and it was the same as being on a long run. As I tell my runners the body only knows what tension you are placing on it and of course does everything it can to grow in ways to take care of that tension.
If I was doing ten x 200 meters with a fifty yard walk and doing them at different speeds, say 2 fresh (5K pace), 2 good build up (start at 5K pace and half way through go to good. (60 second pace), then 1 "Good" (60 second pace). Then repeat the series. After 10 x 100 meters (fresh) I would go to another set. Always choosing on how I felt at that time and how hard the workout would be.
You have to remember that all of us in the 60's had to study or work 8 hours a day. If I could get a rub down after the morning workout and maybe a nap, I am sure it would have made a difference. In the summer of '64 I did not work and everything was easier. Of course most of the good Europeans never had to work. Nothing against them, they were just a few years ahead of us. well maybe 10 or 15. But all of us on the L.A. Track club were fighting for changes in the rules. Remember I was one of the athletes who tried to have the pro-track circuit.
I worked hard three and sometimes four days a week. With 13 workouts (only once on Sunday)it took a lot of time. From the Fall of 63, when I returned to Miami of Ohio, I worked out at 5:30 A.M. and 5:30 p.m. Looking back I was doing close to 100 miles a week, if I didn't have a race.
Are the runners better today than we were? Maybe they are. I think the Kenyans and ethiopians have not only an advantage of having lived at altitude their entire life but their ancestors have lived at altitude for millions of years. Does the body change internally? If it does with training then it must change to be better acclimated. (Boy does that open a can of worms.)