Sub-max effort (90%) HIIT followed by a recovery until the heart reaches 60%.
Develops eccentric heart. Builds muscle on the outside of the left ventricle. It teaches the heart how to beat faster. But also forces the heart to recover faster by letting the blood pool in the left ventricle.
When done correctly, the average heart rate throughout the session sits somewhere around 75%. Making the heart benefits similar to Zone 2 training.
Sub-max effort (90%) HIIT with recovery to 70-80%
Develops a concentric heart, similar to this. The recovery is not sufficient to bring the heart rate down to reap the eccentric benefits.
But also, as the rest is insufficient, can you really reach 90%? Or are you just getting tired for the sake of getting tired? With zero benefits.
Here’s where it’s at
For health, you want a strong eccentric heart with slow and long beats. Combined with concentric capabilities that allow the heart to beat fast when it needs to.