my own experiments over three separate 2-year timeframes and the results are clear enough. Surprisingly less work at mid to higher intensities turned out to deliver more results - lower resting heart rate, improved heart rate variability, higher ftp, stronger power at 2-5 minutes, increased leg muscle mass, improved body composition, etc, etc. And when I go hard, its near max or max and not about racking up more intervals/repeatability (that’s what mid-week worlds are for).
Can’t drink, can’t smoke, can’t eat unhealthy foods, and now I can’t do insane things on the bike for stupid lengths of time? This getting older crap really sucks.