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 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. Bodybuilders use it to build lean muscle mass.

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

What Is the Anaerobic Zone?

One of the primary aims of anaerobic exercise is improving cardiovascular and respiratory capacity. Depending on the goals, the duration of training can 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% of your MHR, around 85% of the consumed calories will be from carbs, 14% from fat, and 1% 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 that is used for both aerobic and anaerobic exercise.

ATP 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.

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."

There are also other benefits of regular anaerobic training.

  • It builds and maintains lean muscle mass while protecting your joints and connective tissue from damage.
  • 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.
  • It can improve your VO2 max (the maximum volume of oxygen you can consume during exercise).
  • It can increase your body's ability to store glycogen, giving you more energy during intense physical activity.
  • 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).

A 2013 study published in the European Journal of Nutrition found that the obese participants who combined anaerobic and aerobic exercise lost more body mass than those who only did aerobic exercise.


Despite the potential benefits to your health, anaerobic exercise can also pose risks— particularly for people with uncontrolled hypertension or underlying heart disease.

Scientists have theorized that excessive anaerobic exercise might contribute to the development of a condition that causes the arteries to harden (atherosclerosis).

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.

One theory is that the ongoing depletion of HGH decreases "good" high-density lipoprotein (HDL) cholesterol while at the same time triggering increases in body mass and high blood pressure.

The evidence is not conclusive, but it is possible that these changes could promote atherosclerosis and other cardiovascular diseases in some people.

Training Methods

You can reach the anaerobic zone 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:

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

A Word From Verywell

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

4 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  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

Additional Reading

By Wendy Bumgardner
Wendy Bumgardner is a freelance writer covering walking and other health and fitness topics and has competed in more than 1,000 walking events.