@rob_dalto: The best way to learn your thresholds is in the lab with a VO2 test, it is by far the most accurate. If that is not accessible, there are a few workouts said to help get a rough idea (do these on different days): VO2 Max: The pace and heart rate from a 9 minute all-out effort. LT2: The average heart rate from a 20-minute time trial. LT1: a pace you can comfortably talk in full sentences.