The following workouts are typically called Over/Unders.
These workouts are characterized by 2 phases:
-an initial interval done at an intensity above Threshold
- followed immediately by an interval done below Threshold.
It is just as important to stay within the Power target on the Under portion as it is on the Over portion.
The reason for this is that these workouts are targeting your ability to clear lactate. The lactate in these workouts is produced during the Over portions and cleared during the Under portions. If the intensity of the Under portion drops too low then you will fail to work this physiological adaptation and obtain the full benefit of the workout.
There are very hard sessions from both a physical and mental standpoint. These workouts should not be done with too much frequency and/or done over long period of time. In other words, limit how many times you do these types of workouts and for how long.
I have been coaching cyclists for over 10 years. I ascribe to the Polarized approach to training. I believe that coaching is more than just science. There is an art to coaching that revolves around coach-athlete interaction.