This thread reminded me of a couple videos I watched about the importance of Intervals and Sprinting. It's a running channel, but can be modified for us cyclists.

In the first video he goes into the history of interval training and it's interesting because interval training has (and still is) used for Aerobic training, if done a certain way, which he covers. You do this by not going all out, nor even going Anaerobic, rather keeping it in the upper limits of the aerobic system, but faster than a tempo workout. Then take a short break and repeat.

It's a good alternative to boring zone 2 rides, but not nearly as fatiguing as how many people do contemporary interval training, where they do go Anaerobic. And it also stimulate more muscle fibers (faster fibers) than typical zone 2 training.







And for comparison he also talks about Sprint training, which of course is all-out speed/power. And this video is for endurance athletes, NOT pure sprinters.