I assume this is the workout described above.

From the article...

“Low” intensity in polarized training is below your aerobic threshold (AeT).

As you might have reckoned by now, the “moderate” intensity in polarized training is the training done between AeT and AnT. So with my heart rate zone system this is zones 2, 3 and 4. With Coggan’s power zone system that’s everything from zone 2 up to FTP.

POL Group. This is the polarized group. They trained with a combination of the HVT and HIIT groups—either very hard of very easy. Also training in three-week blocks, they did two weeks with two HIIT interval sessions each week and with four long sessions done below AeT. Every third week (recovery week) they alternated days off with a single HIIT session and long workouts done below AeT. Their training was unique in that they never did any training between AeT and AnT. Few, if any, athletes train this way.

My interpretation from the article by Friel is that one rides below zone 2 or above zone 4 in polarized training.