I did a lot of 30 / 15 intervals in 2020. My progression was
3 sets of 8 x 30 / 15 with 3 min recovery
3 sets of 9:x 30 / 15 with 3 min recovery
3 sets of 10 x 30 / 15 with 3 min recovery
3 sets of 11 x 30 / 15 with 3 min recovery
3 sets of 12 x 30 / 15 with 3 min recovery
3 sets of 13 x 30 / 15 with 3 min recovery
Works perfectly with two high intensity a week with a three weeks on, one week recovery cycle. Ramp retest then start again at 8 intervals per set hopefully at new higher intensity.
I ended up at 105% of MAP. I did try 108% but that pushed me up to 95-97% but that was too much. So you need to experiment with the number of intervals, the intensity, and the balance of work to rest.
Despite the on / off nature my HR looks like this during the workout. Short recovery doesn’t allow the HR to drop much during a set.
