Originally Posted by Carbonfiberboy

We don't normally train much in that middle zone because it tires one out and doesn't produce results proportionally. Thinking today is to do your endurance work at a level that doesn't exhaust you over time, and then supplement that with HIIT, which increases your ability to cruise at high HR more than anything else. Of course when you're riding an event, you use whatever HR is appropriate, without regard to training.