Originally Posted by
terrymorse
You may burn more fat during a zone 2 session, but zone 2 won't efficiently train muscles to burn fat. To efficiently train for fat burning, you need more muscle mitochondria, and higher intensity builds mitochondria more quickly. Reportedly, zone 4 is twice as efficient than zone 2 at developing mitochondria.
Zone 2 is the best and most effective way to develop and maintain healthy mitochondria. This has already been studied and proven....Higher efforts above Zone 2 are less beneficial for mitochondria and too much HIIT can actually do more harm than good.