Aerobic exercise is physical exercise of relatively low intensity that depends primarily on the aerobic energy-generating process. Aerobic literally means "living in air", and refers to the use of oxygen to adequately meet energy demands during exercise via aerobic metabolism. Generally, light-to-moderate intensity activities that are sufficiently supported by aerobic metabolism can be performed for extended periods of time.
What is Aerobic Exercise?
The American College of Sports Medicine (ACSM) defines aerobic exercise as "any activity that uses large muscle groups, can be maintained continuously, and is rhythmic in nature." It is also defined as exercise that increases the need for oxygen. Aerobic exercise is used interchangeably with the terms: cardiovascular exercise, cardio-respiratory exercise and cardio. Some examples of aerobic exercise include: walking, jogging, running, dancing, rollerblading, bicycling, swimming, aerobics classes (both land and water), rowing, stair climbing, etc.
What are the Benefits of Aerobic Exercise?
Aerobic exercise strengthens your heart and lungs (which make up the cardiovascular system). During exercise, your muscles demand more oxygen-rich blood and give off more carbon dioxide and other waste products. As a result, your heart has to beat faster to keep up. When you follow a consistent aerobic exercise plan, your heart grows stronger so it can meet the muscles' demands without as much effort. Everyone, regardless of their weight, age, or gender, can benefit from aerobic exercise.
Regular aerobic exercise, performed most days of the week, also helps reduce the risk of illness and premature death. Regular aerobic exercise improves health in the following ways:
Reduces body fat and improves weight control
Reduces resting blood pressure (systolic and diastolic)
Increases HDL (good) cholesterol
Decreases total cholesterol
Improves glucose tolerance and reduces insulin resistance
Decreases clinical symptoms of anxiety, tension and depression
Increases maximal oxygen consumption (VO2 max)
Improves heart and lung function
Increases blood supply to the muscles and
Enhances your muscles’ ability to use oxygen
Lowers resting heart rate
Increased threshold for muscle fatigue (lactic acid accumulation)
Source: “Physical Activity and Health: A Report of the Surgeon General”, CDC, 1999.
Aerobic exercise and fitness can be contrasted with anaerobic exercise, of which strength training and short-distance running are the most salient examples. The two types of exercise differ by the duration and intensity of muscular contractions involved, as well as by how energy is generated within the muscle.
In most conditions, anaerobic exercise occurs simultaneously with aerobic exercises because the less efficient anaerobic metabolism must supplement the aerobic system due to energy demands that exceed the aerobic system's capacity. What is generally called aerobic exercise might be better termed "solely aerobic", because it is designed to be low-intensity enough not to generate lactate via pyruvate fermentation, so that all carbohydrate is aerobically turned into energy.
Initially during increased exertion, muscle glycogen is broken down to produce glucose, which undergoes glycolysis producing pyruvate which then reacts with oxygen (Krebs cycle) to produce carbon dioxide and water and releasing energy. If there is a shortage of oxygen (anaerobic exercise, explosive movements), carbohydrate is consumed more rapidly because the pyruvate ferments into lactate. If the intensity of the exercise exceeds the rate with which the cardiovascular system can supply muscles with oxygen, it results in buildup of lactate and quickly makes it impossible to continue the exercise. Unpleasant effects of lactate buildup initially include the burning sensation in the muscles, and may eventually include nausea and even vomiting if the exercise is continued without allowing lactate to clear from the bloodstream.
As glycogen levels in the muscle begin to fall, glucose is released into the bloodstream by the liver, and fat metabolism is increased so that it can fuel the aerobic pathways. Aerobic exercise may be fueled by glycogen reserves, fat reserves, or a combination of both, depending on the intensity. Prolonged moderate-level aerobic exercise at 65% VO2 max (the heart rate of 150 bpm for a 30-year-old human) results in the maximum absolute contribution of fat to the total energy expenditure. At this level, fat may contribute 40% to 60% of total, depending on the duration of the exercise. Vigorous exercise above 75% VO2max (160 bpm) primarily burns glycogen.
Major muscles in a rested, untrained human typically contain enough energy for about 2 hours of vigorous exercise. Exhaustion of glycogen is a major cause of what marathon runners call "hitting the wall". Training, lower intensity levels, and carbohydrate loading may allow to postpone the onset exhaustion beyond 4 hours.
Aerobic exercise comprises innumerable forms. In general, it is performed at a moderate level of intensity over a relatively long period of time. For example, running a long distance at a moderate pace is an aerobic exercise, but sprinting is not. Playing singles tennis, with near-continuous motion, is generally considered aerobic activity, while golf or two person team tennis, with brief bursts of activity punctuated by more frequent breaks, may not be predominantly aerobic. Some sports are thus inherently "aerobic", while other aerobic exercises, such as fartlek training or aerobic dance classes, are designed specifically to improve aerobic capacity and fitness. It is most common for aerobic exercises to involve the leg muscles, primarily or exclusively. There are some exceptions. For example, rowing to distances of 2,000 m or more is an aerobic sport that exercises several major muscle groups, including those of the legs, abdominals, chest, and arms. Common kettlebell exercises combine aerobic and anaerobic aspects.
Among the recognized benefits of doing regular aerobic exercise are:
Strengthening the muscles involved in respiration, to facilitate the flow of air in and out of the lungs
Strengthening and enlarging the heart muscle, to improve its pumping efficiency and reduce the resting heart rate, known as aerobic conditioning
Strengthening muscles throughout the body
Improving circulation efficiency and reducing blood pressure
Increasing the total number of red blood cells in the body, facilitating transport of oxygen
Improved mental health, including reducing stress and lowering the incidence of depression
Reducing the risk for diabetes.
Burns body fat, while building leaner muscle.
As a result, aerobic exercise can reduce the risk of death due to cardiovascular problems. In addition, high-impact aerobic activities (such as jogging or using a skipping rope) can stimulate bone growth, as well as reduce the risk of osteoporosis for both men and women.
In addition to the health benefits of aerobic exercise, there are numerous performance benefits:
Increased storage of energy molecules such as fats and carbohydrates within the muscles, allowing for increased endurance
Neovascularization of the muscle sarcomeres to increase blood flow through the muscles
Increasing speed at which aerobic metabolism is activated within muscles, allowing a greater portion of energy for intense exercise to be generated aerobically
Improving the ability of muscles to use fats during exercise, preserving intramuscular glycogen
Enhancing the speed at which muscles recover from high intensity exercise
Both the health benefits and the performance benefits, or "training effect", require a minimum duration and frequency of exercise. Most authorities suggest at least twenty minutes performed at least three times per week.