While an anaerobic threshold is a fairly well-defined moment – when you are gasping for breath and you can feel lactic acid making your muscles sting – your aerobic threshold is more often described as a “zone” in which your heart is working from 70 to 80 percent of your maximum heart rate. To reach this level, you are probably running or otherwise exercising vigorously. Your maximum heart rate can be roughly calculated as 220 minus your age, and at 70 percent of that point you are starting to sweat and having trouble talking in full sentences.
Entering the Aerobic Zone
When you are exercising aerobically, your body is able to supply your working muscles with all the oxygen and energy they need. You may be walking, jogging lightly or even running, but as long as you don't increase your pace too much, your body can continue for a long time. Aerobic exercise is any activity that uses large muscle groups and elevates your heart rate to 50 percent to 80 percent of your maximum heart rate. Another way to tell if you are in this zone is the talk test: at an easy pace you can sign a song, but at the higher reaches of aerobic exercise you can barely utter a short sentence.
The Anaerobic Sting
When you breach the anaerobic threshold, however, it’s difficult to talk and your muscles are asking for more oxygen and energy than your body can supply. Your muscles begin to sting and then to ache and very quickly they are no longer able to continue contracting and you have to stop. At this intensity, your heart rate is higher than 80 percent of its maximum and may be at 90 percent or higher.
Expanding the Zone
One goal of exercise is to stretch your aerobic zone by training your body to work aerobically at higher and higher heart rates. You can accomplish this with “tempo” workouts, where you train at a heart rate just below your anaerobic threshold for an extended session, and “interval” workouts, where you train for shorter periods of time but push your heart rate above the anaerobic threshold. These intervals are broken up by recovery periods in which you go easy.
Tempo and Intervals
The best training programs add these tempo and interval workouts after a period of high volume training. High volume training is done at a light intensity level and should only be increased gradually by 10 to 20 percent per week until you reach the volume you want to maintain. When you add tempo and interval workouts, each should constitute no more than 10 percent of your high volume training, and they never should be done on consecutive days.