In physical exercise, aerobic exercise is complementary to anaerobic exercise. Aerobic literally means "with oxygen", and refers to the use of oxygen in muscles' energy-generating process. Aerobic exercise includes any type of exercise, typically those performed at moderate levels of intensity for extended periods of time, that maintains an increased heart rate. In such exercise, oxygen is used to "burn" fats and glucose in order to produce adenosine triphosphate, the basic energy carrier for all cells. Initially during aerobic exercise, glycogen is broken down to produce glucose, but in its absence, fat starts to decompose instead. This 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, where 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" after only 300 meters.
There are various types of aerobic exercise. In general, aerobic exercise is one performed at a moderately high 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.
Regular, vigorous aerobic activity can, as a result, 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 women and men.
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 after the 1970 publication of Dr. Cooper's book The New Aerobics, 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 describes the functional status of the cardiorespiratory system, including, for example, the heart, lungs or blood vessels. Aerobic capacity is defined as the maximum volume of oxygen which can be consumed by ones muscles during exercise. It is a function both of ones 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 typically directs a subject to exercise on a treadmill, first by walking at an easy pace and then, at set time intervals during graded exercise tests, gradually increasing the workload. The higher a cardiorespiratory endurance level, the more oxygen transported to exercising muscles and the longer exercise can be maintained without exhaustion. The higher aerobic capacity, the higher the level of aerobic fitness.