When you exercise, your body produces lactic acid as a byproduct. If you're exercising at a low intensity, your body is able to quickly clear this byproduct. However, when you begin to cycle at a more intense rate, it becomes increasingly more difficult for your body to clear the lactic acid. The point at which the body produces more of this byproduct than it can clear is called the lactate threshold. This point, which occurs at about 85 percent of your maximum heart rate, can be measured with a heart-rate monitor. A cyclist will also feel a burning sensation in her muscles when she is over her lactate threshold and her body begins to tire. Identifying your lactate threshold will help you learn to pace your efforts and to train smarter.
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Set up your bike in a trainer indoors or find a flat to rolling route outside to perform the test. When performing the test outside, be sure to plan a route that's free of stop signs, stop lights and heavy traffic. This is an intense exercise and it's important to keep working at a certain level of exertion for the prescribed period of time without any interruptions.
Warm up, pedaling in an easy gear for at least 15 minutes. Try to keep a cadence of 90 rpm. You can measure this using a cycling computer with cadence. Allow your body to become loose, relax your upper body and breathe deeply to prepare your muscles for the work ahead.
Perform a short sprint, getting out of the saddle. When you sit down, focus on pushing a gear at a pace you can hold for an hour. This will be your one hour time trial pace. Focus on keeping this nice, steady pace, at 90 rpm.
Time yourself. After 10 minutes at this time-trial pace, hit the lap button on your heart-rate monitor. Maintain the pace you have set for 20 more minutes. Breathe as you pedal. This is not an all-out effort, but you should be pushing yourself to maintain the pace. Try to avoid using a gear that will quickly tire you out.
Press the lap button again after the 20 minutes is over. This is the end of the test. Cool down by using an easy gear. You should feel your heart rate dropping. Pedal for five to 10 minutes, depending on how your body feels. Read the average heart rate for the 20-minute time trial you just completed. This is your lactate threshold. Use this number to help with your future training.