How to Reach the Anaerobic Zone During Exercise

How the Depletion of Oxygen Increases Performance

Female runner checking heart rate monitor

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Anaerobic simply means "in the absence of oxygen." Unlike aerobic exercise, which relies on oxygen to convert calories into energy, anaerobic exercise involves short bursts of intense physical activity during which the oxygen demands exceed the oxygen supply.

Anaerobic exercise is used by non-endurance athletes to increase strength, power, and speed and by bodybuilders to build lean muscle mass.

You can tell if you are in an anaerobic state if you are between 80 percent and 90 percent of your maximum heart rate (MHR). At this exertion level, you will be breathing very hard and will unable to speak in full sentences.


One of the primary aims of anaerobic exercise is to improve your cardiovascular and respiratory capacity. Depending on the aims of training, the duration of training may be as short as a few seconds (such as for power-lifting) or as long as several minutes (for sprinting, hurdles, speed skating, etc.)

In the anaerobic zone, carbohydrates are burned more readily than fats. At 80 to 90 percent of your MHR, around 85 percent of the consumed calories will be from carbs, 14 percent from fat, and 1 percent from protein.

Rather than relying on oxygen, anaerobic exercise is fueled by glycogen, a carbohydrate stored in muscles. At the molecular level, glycogen contains oxygen, hydrogen, and carbon. Through a process known as glycolysis, glycogen is broken down into adenosine triphosphate (ATP), a complex cellular energy source, used for both aerobic and anaerobic exercise.

This provides the body with a quick burst of energy while triggering the rapid build-up of lactic acid, a byproduct of glycolysis. Lactic acid is the substance that causes your muscle to fatigue during a heavy workout. In fact, the burning sensation you feel in your muscles after strenuous activity is the result of lactic acid accumulation.


One of the benefits of anaerobic exercise is that your body will be able to handle lactic acid more efficiently. If you regularly push yourself into the anaerobic zone, your body will begin to clear lactic acid faster than it is produced. This is known as lactate threshold training.

If your body is unable to clear it faster than it is being produced, you will quickly fatigue and reach your so-called anaerobic threshold. Runners often refer to this as "hitting the wall."

Among some of the other benefits of regular anaerobic training:

  • It builds and maintains lean muscle mass while protecting your joints and connective tissue from damage.
  • It can increase your body's ability to store glycogen, giving you more energy during intense physical activity.
  • It can improve your VO2 max (the maximum volume of oxygen you can consume during exercise).
  • It can increase the strength and density of your bones more than any other type of exercise, decreasing the risk of osteoporosis (bone mineral loss).
  • It boosts metabolism and helps promote weight loss. Lean muscle is metabolically active, meaning that the more there is, the faster the calories will be burned.

A study published in the European Journal of Nutrition concluded that obese people who combined anaerobic exercise with aerobic exercise achieved greater losses in body mass than those who did aerobic exercise alone.


Despite its benefits to your health, anaerobic exercise poses potential risks, particularly in people with uncontrolled hypertension or underlying heart disease. Some scientists have also theorized that excessive anaerobic exercise may contribute to the development of atherosclerosis (hardening of the arteries).

According to a study in Applied Physiology, Nutrition, and Metabolism, anaerobic exercise can lead to decreases in human growth hormone (HGH), a naturally occurring substance that helps with cellular repair.

It has been theorized that ongoing depletions of HGH can decrease "good" high-density lipoprotein (HDL) cholesterol while triggering increases in body mass and high blood pressure. While the evidence is far from conclusive, it is possible that these changes can promote atherosclerosis and other cardiovascular diseases.

Training Methods

The anaerobic zone can be reached through high-intensity exercises such as running, cycling or speed swimming. It can also be achieved with interval training, in which you intersperse bursts of high-intensity exercise with short bouts of moderate-intensity exercise.

Lactic threshold training may involve either of these two strategies. By comparison:

  • Steady-state anaerobic exercise, also known as a tempo workout, involves gradually increasing the intensity of exercise until you reach 80 to 90 percent of your MHR. You would then maintain that level for anywhere from two to 20 minutes before the cool-down.
  • Interval anaerobic exercise, also known as high-intensity interval training (HIIT), aims to push your body to fatigue by alternating high-intensity and low-intensity exercises up to or near your anaerobic threshold.

A Word From Verywell

If you are new to exercise, do not start with high-intensity anaerobic workouts. Focus instead on lower-intensity aerobic exercise for at least 12 weeks, pushing yourself to no more than 60 or 70 percent of your MHR by week 12. Always check with your doctor before adding anaerobic exercise to any fitness program.

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  1. Patel H, Alkhawam H, Madanieh R, Shah N, Kosmas CE, Vittorio TJ. Aerobic anaerobic exercise training effects on the cardiovascular system. World J Cardiol. 2017;9(2):134-138. doi:10.4330/wjc.v9.i2.134

  2. Scott CB. Contribution of anaerobic energy expenditure to whole body thermogenesis. Nutr Metab (Lond). 2005;2(1):14. doi:10.1186/1743-7075-2-14

  3. Agrotou S, Karatzi K, Papamichael C, et al. Effects of chronic anaerobic training on markers of sub-clinical atherosclerosis. Hellenic J Cardiol. 2013;54(3):178-85.

  4. Mehanna E, Hamik A, Josephson RA. Cardiorespiratory Fitness and Atherosclerosis: Recent Data and Future Directions. Curr Atheroscler Rep. 2016;18(5):26. doi:10.1007/s11883-016-0580-7

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