Determine your lactate threshold, the point that your body can no longer clear lactate, a byproduct from intense exercise and produced in the blood. To do this, jump on your bike trainer or find a repeatable route that is flat or with a slight steady grade. You do not want hills or rolling terrain. Warm the legs for 20 minutes. After 20 minutes, start your heart rate monitor. Ten minutes into your sustainable but hard effort, hit the start lap button on your heart rate monitor. Record your heart rate for another 20 minutes. This will be your lactate threshold, and you should feel gassed at the very end of the test.
Cyclists should focus on five heart rate zones. In zone one, riders are at 65 percent of their lactate threshold; zone one is geared toward slow recovery rides. In zone two, a cyclist is at 65 percent to 72 percent of LT; this zone is typical for longer endurance rides. For higher end aerobic activity, zone 3 should be performed at 73 percent to 80 percent. To be at your lactate threshold, stay in zone 4 -- between 84 percent and 90 percent. Zone five -- 91 percent to 100 percent -- is for anaerobic training and sprints.
Retest your lactate threshold on the same course every six to eight weeks to track improvement. Proper training will build your efficiency at the same heart rate.