You may be more familiar with Maffetone's Method than I am. I had thought he didn't "approve" any higher intensity stuff. But it has been a while since I read anything from him, so I may be misremembering - or he may have changed his position.Even then, (if I understand it correctly) Maffetone recommends that the individual perform the vast majority of their ‘aerobic’ activity at this level; (MAF) but not all of it. This aligns with what others (Uphill Athlete, etc.) also recommend. It also aligns very well with my personal experiences…