The classic Harm and Hickson study:
The bottom line is that my first coach (who said some old-school Dutch dumb stuff, and some time-proven smart stuff…the hard part was filtering out the first to get the second) used to say “the more contractions, the more reactions,” and in the case of adding volume, he was right.
Doing the extra endurance harder – say 70% rather than 60% – after you’re done with the intervals is not going to enhance the endurance adaptations – it’s just going to increase fatigue. Add endurance, but no need to clobber yourself in doing it.
- Do the zone 5 intervals or higher on fresh legs, and do the endurance “fill” after.
- Some some sweet spot or threshold intervals on fresh legs, but also do some in the 2nd half/last hour of the workout for the “tired 20” benefits discussed above.
Doing the zone 2 harder drives up CTL, but remember that CTL is just a metric for training load, not for fitness. For zone 2 watts, more time at the lower % of FTP will be of more long-term benefit than less time at a higher %.