Anaerobic exercise is a type of exercise that is short in duration but high in intensity. Because of its high intensity, anaerobic exercise demands more oxygen than is available within the body. For that reason, this type of exercise relies on energy that has been stored in muscles. Thus, anaerobic exercise generates energy through metabolic means within the body, primarily the muscles, without the sole use of oxygen.

Physical exercise can be divided into two types: aerobic and anaerobic. Aerobic exercise demands increased oxygen use; whereas anaerobic, as the word itself indicates, is performed without oxygen. Individuals engaged in anaerobic exercise breathe, but the exercise itself depends on muscles, not oxygen. In weight lifting, for example, muscles generate so much energy that the blood stream cannot supply enough oxygen to the muscles for them to do their work. Instead of needing only oxygen (as in aerobic exercise), muscles in anaerobic exercise use fuel stored in the body.

Examples of anaerobic exercise include rock climbing, interval training, isometrics, and sprinting, along with such sports as basketball, football, hockey, rugby, and soccer. Thus, anaerobic exercise—sometimes called muscle strengthening, strength building and flexibility, or strength training—is any activity or sport that involves brief spurts of intense, difficult activity that typically lasts from a few seconds to about two minutes.

One example of anaerobic exercise is interval training. It is performed in numerous ways, such as in bicycling, swimming, and running. Interval training Page 55  |  Top of Articleis accomplished in a series of steps: the exercise pace is increased greatly for a short period, such as ten seconds to one minute, and then a recovery period is initiated that is at least three times as long as the strenuous exercise period. This cycle is repeated usually several times over a longer period of time.

Lifting weights is one example of anaerobic exercise, which is performed at a high intensity, using a limited number of muscles, for a short period of time. Anaerobic exercise helps to build muscle mass, strength, and power. (wavebreakmedia/Shutterstock.com) (wavebreakmedia/Shutterstock.com)

Anaerobic exercise builds muscle mass and strength, but it does not build endurance. In other words, it is not performed over long stretches of time as in long-distance running. Anaerobic exercise makes muscles stronger and larger, as seen in bodies of weight-lifters and body builders and football and rugby players. It also prepares the muscles to respond quickly, such as is needed for a wide receiver in football whose leg muscles go from rest to maximum speed in just a few seconds to catch a pass from his quarterback. Anaerobic exercise also develops flexibility and agility.

Anaerobic exercise increases oxygen uptake, what is commonly called VO2 max. The term refers to the maximum amount of oxygen that an individual can use during intense exercise. Anaerobic exercise also increases the body's ability to withstand waste build up and the body's ability to remove those waste substances. Such ability helps individuals to fight off fatigue in any strenuous activity.

Many people in their middle years choose to participate in anaerobic exercise to stay in good physical fitness. Without regular use, as provided by anaerobic exercise, muscles lose their ability to work and atrophy (shrink). However, anaerobic exercise can be harmful to older people because of its effect on blood pressure. Anaerobic exercise is also not suitable for young children.

In 1996, the U.S. Surgeon General first reported on physical activity and health for Americans. In part, The main message of this report is that “Americans can substantially improve their health and quality of life by including moderate amounts of physical Page 56  |  Top of Articleactivity in their daily lives.” The report added, “Health benefits from physical activity are thus achievable for most Americans, including those who may dislike vigorous exercise and those who may have been previously discouraged by the difficulty of adhering to a program of vigorous exercise.” However, according to the U.S. Centers for Disease Control and Prevention (CDC), only 20.9% of American adults 18 years and older, met the federal Physical Activity Guidelines for both aerobic and nonaerobic exercise in 2015.

In anaerobic exercise, oxygen is in short supply, so a metabolic breakdown of glycogen into glucose must occur in a process called anaerobic glycolysis (what is known as the breakdown of glucose). During this time the muscles quickly fatigue from the amount of work asked of them. The fatigue causes a burning sensation in the muscles. Although lactic acid (or lactate) is often blamed for the sense of fatigue and the burning sensation in the muscles, it is not the cause. Fatigue and lactate increase as the intensity of exercise increases. What happens is that as soon as lactic acid is produced in the body, it changes into lactate and hydrogen. The body actually uses lactate as a source of energy for the muscles. Consequently, it is not the cause of fatigue during anaerobic exercise. Hydrogen may contribute to fatigue, but it is only a minor contributor.

Medical research indicates that fatigue during anaerobic exercise and other nonsustainable activities is likely caused primarily by an accumulation of metabolites such as inorganic phosphate within the muscles and the inability of the muscles to maintain the high rate of contractions and the excessive force that comes from those contractions, which also results in large amount of potassium being lost within the muscles. Potassium, a primary electrolyte, helps to transport glucose to the cells of the muscles. When depleted in the muscles, potassium deficiency can cause cramping, spasms, and weakness. Nausea and vomiting can also occur.

Preparation for anaerobic exercise entails warming up, by performing the exercise slowly and by stretching. For maximum benefit from such exercises, make sure to get plenty of rest each night and drink plenty of water each day. Two sessions of anaerobic exercise are generally recommended each week.

Risks from anaerobic exercises can be minimized by first seeking medical advice from a family doctor or other trusted medical professional, such as an exercise physiologist, before starting any anaerobic exercise regimen. Advice and physical examination will assure that the body is ready for exercise and that during the exercises the risk of injury is minimized. Three of the largest risks of anaerobic exercises are starting too quickly, working out for too long, and performing too intensely.

The most strenuous anaerobic exercises involve interval training. These exercises are performed by individuals trying to increase their muscle strength, such as weight lifters; to run the fastest, such as with sprinters; and to be the most powerful, as with football linebackers. When performing interval training, the muscles become tired and, consequently, these individuals experience the most discomfort. Beginners at anaerobic exercise should not attempt such training but should perform more modest degrees of anaerobic exercise for several weeks in order to build up fitness before starting more strenuous forms of anaerobic exercises.

Anaerobic exercise should be performed at a rate that feels right. If an increased rate does not have any adverse side effects, then both the intensity of the activity and its time duration are appropriate and increases can be initiated. However, if negative side effects occur, the rate is too high in too brief a period. It is advisable to back off on duration and intensity.

In addition, it is not recommended for pregnant women to perform anaerobic exercises, especially strenuous ones. Whether one is an advanced or beginning anaerobic exerciser, always warm up first, and stretch before and after workouts. A cool down of five to ten minutes is usually advised by fitness trainers.

The result of anaerobic exercise is an improved set of muscles—those having more strength and mass. The cardiovascular-respiratory system of the body, including the heart and lungs, is also improved because the body uses oxygen more efficiently when conditioned to do so with anaerobic exercise.

Generally, anaerobic exercise burns fewer calories than aerobic exercise and is less helpful for achieving cardiovascular fitness than is aerobic exercise. However, it is better at building strength and mass in muscles and bones.