Aerobic exercise

Aerobic exercise refers to exercise which is of moderate intensity, undertaken for a long duration. Aerobic means "with oxygen", and refers to the use of oxygen in a muscle's energy-generating process. Many types of exercise are aerobic, and by definition are performed at moderate levels of intensity for extended periods of time.

An effective aerobic exercise should involve 5-10 minutes of warming up at an intensity of 50-60% of maximum heart rate, followed by at least 20 minutes of exercise at an intensity of 70-80% of maximum heart rate, ending with 5-10 minutes of cooling down at an intensity of 50-60% of maximum heart rate.

History
Both the term and the exercise method were developed by Kenneth H. Cooper, M.D., an exercise physiologist of the U.S. Air Force. Dr. Cooper, an avowed exercise enthusiast, was personally and professionally puzzled about why some people with excellent muscular strength were still prone to poor performance at tasks such as long-distance running, swimming, and bicycling. He began measuring systematic human performance using a bicycle ergometer, and began measuring sustained performance in terms of the ability to utilize oxygen.

His groundbreaking book, Aerobics, was published in 1969, and included scientific exercise programs using running, walking, swimming and bicycling. The book came at a fortuitous historical moment, when increasing weakness and inactivity in the general population was causing a perceived need for increased exercise. It became a best seller.

Cooper's data provided the scientific baseline for almost all modern aerobics programs, most of which are based on oxygen-consumption equivalency.

Aerobic versus anaerobic exercise
Aerobic exercise and fitness can be contrasted with anaerobic exercise, of which strength training and weight training 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.

Initially during aerobic exercise, glycogen is broken down to produce glucose, but in its absence, fat metabolism is initiated instead. The latter is a slow process, and is accompanied by a decline in performance level. The switch to fat as fuel is a major cause of what marathon runners call "hitting the wall".

Anaerobic exercise, in contrast, refers to the initial phase of exercise, or any short burst of intense exertion, in which the glycogen or sugar is consumed without oxygen, and is a far less efficient process. Operating anaerobically, an untrained 400 meter sprinter may "hit the wall" short of the full distance.

There are various types of aerobic exercise. In general, aerobic exercise is one performed at a low to moderate level of intensity over a 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 doubles tennis, with their more frequent breaks, may not be.

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
 * Toning muscles throughout the body, which can improve overall circulation and reduce blood pressure
 * Increasing the total number of red blood cells in the body, to facilitate transport of oxygen throughout the body

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 jumping rope) can stimulate bone growth, as well as reducing 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

Aerobic exercise versus aerobics
"Aerobics" are a particular form of aerobic exercise. Aerobics classes generally involve rapid stepping patterns, performed to music with cues provided by an instructor. This type of aerobic activity became quite popular in the United States after the 1970 publication of The New Aerobics by Dr. Kenneth H. Cooper, and went through a brief period of intense popularity in the 1980s, when many celebrities (such as Jane Fonda and Richard Simmons) produced videos or created television shows promoting this type of aerobic exercise. Group exercise aerobics can be divided into two major types: Freestyle Aerobics and Pre-choreographed aerobics.

Aerobic capacity
'Aerobic capacity' describes the functional status of the cardiorespiratory system, (the heart, lungs and blood vessels). Aerobic capacity is defined as the maximum volume of oxygen that can be consumed by one's muscles during exercise. It is a function both of one's cardiorespiratory performance and of the ability of the muscles to extract the oxygen and fuel delivered to them. To measure maximal aerobic capacity, an exercise physiologist or physician will perform a VO2 max test, in which a subject will undergo progressively more strenuous exercise on a treadmill, from an easy walk through to exhaustion. The individual is typically hooked up to a respirometer to measure oxygen, and the speed is increased incrementally over a fixed duration of time. The higher a cardiorespiratory endurance level, the more oxygen transported to exercising muscles, the longer exercise can be maintained without exhaustion and accordingly the faster they are able to run. The higher aerobic capacity, the higher the level of aerobic fitness. The Cooperand multi-stage fitness tests can also be used to functionally assess aerobic capacity. In most people, aerobic capacity can be improved through a variety of means, including Fartlek training.

The degree to which aerobic capacity can be improved by exercise varies very widely in the human population: while the mean response to training is an approximately 17% increase in VO2max, in any population there are "high responders" who may as much as double their capacity, and "low responders" who will see little or no benefit from training. Studies indicate that approximately 10% of otherwise healthy individuals cannot improve their aerobic capacity with exercise at all. The degree of an invididual's responsiveness is highly heritable, suggesting that this trait is genetically determined.

Criticisms
When generalized fitness is a professional operational requirement, as for athletes, combat services, police and fire personnel, aerobic exercise alone may not provide a well-balanced exercise program. In particular, muscular strength, especially upper-body muscular strength, is usually neglected. Also, the metabolic pathways involved in anaerobic metabolism (glycolysis and lactic acid fermentation) that generate energy during high intensity, low duration tasks such as sprinting, are not exercised at peak rates. Aerobic exercise is, however, an extremely valuable component of a balanced exercise programme and is good for cardiovascular health.

Some persons suffer repetitive stress injuries with some forms of aerobics and then must choose less injurious "low-impact" forms or lengthen the gap between bouts of aerobic exercise to allow for greater recovery.

Aerobics notably does not increase the resting metabolic rate as much as some forms of weight-training, and may therefore be less effective at reducing obesity. However, this form of exercise also allows for longer, more frequent activity and consumes more energy when the individual is active. In addition, the metabolic activity of an individual is heightened for several hours following a bout of aerobic activity.

Aerobic activity is also used by individuals with anorexia as a means of suppressing appetite, since aerobic exercise increases glucose and fatty acids in the blood by stimulating tissues to release their energy stores. While there is some support for exercising while hungry as a means of tapping into fat stores, most evidence is equivocal. In addition, performance can be impaired by lack of nutrients, which can impair training effects.

Commercial success
Aerobic exercise has long been a popular form of weight loss and physical fitness, often taking a commercial form.


 * Tennis and jogging gained prominence and popularity in the 1970s
 * Judi Sheppard Missett largely helped create the market for commercial aerobics with her Jazzercise program in the 1970s
 * Richard Simmons hosted an aerobic exercise show on television, beginning in the 1980s, and continued with a variety of exercise videos.
 * Billy Blanks's Tae Bo helped popularize cardio-boxing, workouts that used martial arts movements in the 1990s
 * The Nia Technique, also called Neuromuscular Integrative Action, was developed in the 1980s as a form of "non-impact" aerobics (the original words in the acronym). This is in contrast to   popular "no pain no gain" attitudes, and attempted to combat the problem of impact injuries.