alt Hacker NewsAs an anecdote of one, I was doing moderate intensity endurance exercise for a couple years with only modest improvements in basic cardiovascular metrics that kind of flatlined over time.
As an experiment, I switched to high-intensity interval type training for a couple months, which required about half the time to do. All of my cardiovascular metrics immediately changed in a strongly positive way. When I did the old endurance training, performance was much higher than it had been before the high-intensity training.
It is the strongest positive effect I have ever seen from any exercise/gym theory that has been widely promulgated. I never expected to see my cardiovascular metrics change as quickly or as much as they did.
You probably spent all that time training your cardiovascular base, which takes a long time to do. Then, you capped them off with anaerobic gains that were only possible with that prior work.
For optimum gain you should mix moderate exercise with intense exercise, but the time you put in likely made your later success possible.