I found training with a hr monitor to be incredibly useful. I know my max hr, and I try to mix my rides and aim to hit the target zone. I have a few work-outs that I use, some for endurance, some for fat burning, and some for power/sprint. Even though I have a powertap aso, I use th hr monitor more. It's true, you ride slw to ride fast, if you can manage yourself and stay in the target zones.