موضوع مقاله: ايروبيك

Aerobic exercise refers to exercise that involves or improves oxygen consumption by the body.^[1] Aerobic means "with oxygen", and refers to the use of oxygen in the body's metabolic^[2] or energy-generating process. Many types of exercise are aerobic, and by definition are performed at moderate levels of intensity for extended periods of time. To obtain the best results, an aerobic exercise session involves a warming up period, followed by at least 20 minutes of moderate to intense exercise involving large muscle groups, and a cooling down period at the end.

History

Both the term and the specific exercise method were developed by Kenneth H. Cooper, M.D., an exercise physiologist, and Col. Pauline Potts, a physical therapist, both of the United States 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 1968, 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, which is then broken down with the help of oxygen to generate energy. In the absence of these carbohydrates, fat metabolism is initiated instead. The latter is a slow process, and is accompanied by a decline in performance level. This gradual 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 to 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.

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 doubles 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.

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
* 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

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

"Aerobics" is 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 amount of oxygen the body can use during a specified period, usually during intense exercise.^[3] It is a function both of cardiorespiratory performance and the maximum ability to remove and utilize oxygen from circulating blood. 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 connected to a respirometer to measure oxygen consumption, and the speed is increased incrementally over a fixed duration of time. The higher the measured cardiorespiratory endurance level, the more oxygen has been transported to and used by exercising muscles, and the higher the level of intensity at which the individual can exercise. More simply stated, the higher the aerobic capacity, the higher the level of aerobic fitness. The Cooper and multi-stage fitness tests can also be used to assess functional aerobic capacity for particular jobs or activities.

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.^[4] Studies indicate that approximately 10% of otherwise healthy individuals cannot improve their aerobic capacity with exercise at all.^[5] The degree of an individual's responsiveness is highly heritable, suggesting that this trait is genetically determined.

Criticisms

When overall fitness is an occupational requirement, as for athletes, combat services, and police and fire personnel, aerobic exercise alone may not provide a well balanced exercise program. In particular, muscular strength, especially upper-body muscular strength, may be 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 program and is good for cardiovascular health.^{[citation needed]}

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 basal 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 word is in the acronym). This is in contrast to popular "no pain no gain" attitudes, and attempted to combat the problem of impact injuries.

Injuries associated with aerobic dance

Injuries Associated with Aerobic Dance An estimated 24 million Americans participate in aerobic dance. A typical workout consists of a warm-up, at least 30 minutes of continuous vigorous activity and a cool-down session. The best aerobic dance programs emphasize flexibility and utilize principles of exercise physiology, such as self-monitoring of pulse. [1] Although aerobic dance can be performed solo, the camaraderie that develops in aerobic dance classes is a major impetus to its popularity. Better cardiovascular health, [2] weight control, improved muscle tone and simply feeling better are strong motivating factors. [3]

Etiology of Injuries

It is useful to classify injuries as overuse or traumatic. Overuse injuries occur when a structure is exposed to repetitive force beyond the abilities of that structure to withstand the force, [4] whereas traumatic injuries are due to sudden overload. The repetitive activities in aerobic dance lead to far more overuse injuries than traumatic injuries. For example, in a study at the University of Illinois, 77 percent of the 52 aerobic dance injuries were overuse injuries (Table 1). Like other weight-bearing activities, aerobic dance leads to injuries almost exclusively in the lower extremities (Figure 1).

Inherent structural or biomechanical factors, including previous injuries, muscle imbalances, concurrent medical problems and musculoskeletal disorders such as overpronation, make some participants more vulnerable to injury. Poor exercise practices, such as lack of conditioning, exercising intensely without a warm-up or resuming activity too rapidly after a layoff, frequently lead to injury. [5] Simply doing too much increases the risk of injury. Some studies show high injury rates in instructors, who may perform aerobic dance for several hours a day. [6] Concurrent participation in other weight-bearing sports or being carried away by group enthusiasm and the music may push some people to injury.

Equipment and environment--footgear and floor surface--are also important factors in aerobic dance injuries. Although there is no agreement about the merits of aerobic dance shoes versus court or running shoes, common sense dictates that a well-constructed athletic shoe with adequate support and shock absorbency is preferable to bare feet or flimsy, worn-out shoes. The ideal dance surface combines stability and resilience: well-padded concrete floors and wood-over-airspace floors are preferable to bare linoleum or concrete floors. [5,6]

Evaluation

Table 2 summarizes the important points in the history and physical examination in patients presenting with aerobic dance injuries. A good history can localize the problem, differentiate between overuse and traumatic injuries, and identify etiologic factors. Overuse pain is generally gradual in onset; falls or twists cause traumatic injuries. Historical details, such as the degree of impairment and aggravating actions (for example, twisting or kicking movements), are helpful in grading the severity of the injury. Details of the exercise itself, including description of the equipment used, may uncover avoidable risk factors.

Physical examination should begin at the site of symptoms, with inspection and palpation, looking for discoloration, tenderness, crepitation and swellig. Involved joints should be checked for effusion and for range of motion, with painful motions noted. Biomechanical screening should include an assessment of muscle strength, leg length measurement, and assessment of gai and alignment of the feet and patellae. Severe injuries or pre-existing problems may mandate circulatory and neurologic evaluation.

Radiographs may be indicated (1) in patients with point tenderness on a bone, (2) in patients with persistent pain for at least three weeks and possible stress fractures or (3) in patients with possible arthritis. Persistent joint pain, especially with effusion, may warrant labortory tests for inflammatory arthritis.

Treatment

Determining the grade of traumatic and overuse injuries is a guide for treatment and rehabilitation. Tables 3 and 4 [7,8] outline grading systems for traumatic and overuse injuries. Since most aerobic dance injuries are of the overuse type, and since the same principles of rehabilitation and correction of risk factors apply to both types of injury, this discussion of the treatment will focus on overuse injuries. Numerous resources detail specific injuries. [9]

Overuse injuries should be treated with ice applications in the form of ice massage and/or an ice pack for 20 minutes at a time. If nonsteroidal anti-inflammatory drugs (NSAIDs) are prescribed, the patient should take regular doses for at least one week. Common sense determines the necessity for any limitation of activity and the resumption of full activity. The patient should have complete pain-free range of motion before resuming low-intensity workouts, with progressively increased intensity as tolerated. To maintain cardiovascular conditioning, alternative exercises, such as swimming or cycling, may be substituted for aerobic dance during a layoff.

• Cooper, Kenneth C. The New Aerobics. Eldora, Iowa: Prairie Wind.
• Donatelle, Rebecca J. Health: The Basics. 6th ed. San Francisco: Pearson Education, Inc. 2005.
• Hinkle, J. Scott. School Children and Fitness: Aerobics for Life. Ann Arbor, MI: ERIC Clearinghouse on Counseling and Personnel Services.