Exercise is the exertion of the body to achieve a physical purpose. Physical movements, no matter how structured, will require a period of rest to permit the body to be restored to a state where it can exercise once more. The observance of the fundamental rules concerning the perpetual process of exercise and recovery is essential to sport success; tired athletes can not train or compete at their highest possible level if they have not permitted themselves recovery.
All exercise, whether viewed as the workout on a particular day, or as part of a larger program or training system, has a built in recovery factor. Aerobic sports are those where the duration of the activity is relatively long, but not indefinite. Recovery from the aerobic exercise begins the moment that the activity ceases. Anaerobic sports are built on short intervals that naturally presume a rest or recovery space between them.
The length of the recovery period in relation to the active exercise period is a function of both the duration of the exercise as well as the intensity level at which the body performs the exercise. Assuming a constant level of fitness, the recovery period to follow a 10-mi (16 km) walk would be expected to be shorter than that following a 10-mile run at the maximum pace that the athlete can sustain.
Exercise recovery has four specific divisions, each of which has its own recovery principles. The divisions are: musculoskeletal recovery from the stresses and forces of training and competition; recovery of the large-scale systems that power the body during exercise, particularly the cardiovascular and cardiorespiratory systems; restoration of the energy stores depleted by exercise, especially carbohydrates and minerals; and psychological recovery often necessitated when competitive and training stresses place a mental burden on the athlete over a period of time.
Sore muscles and joints are the easiest aspect of any athlete to identify as being in need of a recovery period after training sessions or competition. One of the great challenges of athletic participation is a true understanding of the difference in the signals sounded by the body between the pain of an injury, physiological damage requiring decisive treatment and rehabilitation including probable enforced rest, and discomfort caused by exercise, which can be borne or otherwise tolerated as the athlete continues to perform at the highest level possible. The further an athlete advances in a particular discipline, the more often this decision will arise.
Muscle recovery is achieved by the athlete in a number of ways. Rest is the easiest solution to overtaxed muscles; therapy such as massage and various stretching programs suited to the muscle group in question; cool down stretches ease the body to recovery after vigorous workouts by taking the muscles gently through a full range of motion and help prevent cramping and stiffness. In the period following a hard workout or competition, cross-training exercises will serve to keep the body working, thus maintaining over all fitness, while not unduly stressing the muscles that were most stressed by the activity. Examples of effective cross training as a recovery tool are swimming or cycling after an event such as a run, or as a respite from a vigorous contact sport such as rugby.
Recovery of the cardiovascular and cardiorespiratory systems is achieved through a reduction in the intensity of activity through the recovery period. The heart, the organ central to the function of both systems, rarely will benefit from a recovery program that eliminates any stress on it above the sedentary level. It is the body's fluid level, primarily water, that is critical to the recovery of the cardiovascular system, as the reduction of body fluid that occurs through the heat generated by exercise will correspondingly reduce the volume of fluid in the blood plasma, which lessens the ability of the blood vessels to transport oxygen, fuel in the form of glucose and other nutrients throughout the body. When an athlete has lost from 2% to 3% of their body weight in fluids, the recovery of the cardiovascular system to an optimal fluid level can take several hours; the recovery of depleted minerals (such as sodium) to assist in the operation of the cardiovascular system may be a longer process, depending upon how much mineral was depleted. Fluid level recovery is one part of the bodily equation, the restoration of the energy available for exercise is the other.
The restoration of depleted energy stores will commence the moment that carbohydrates are consumed after the activity, either through energy drinks or by way of food. A return to the athlete's usual level of carbohydrates is a process that depends on the carbohydrates present in the foods consumed, and the level of physical activity in the rest period that may draw on these energy stores.
The recovery of the muscles, body systems, and energy stores of an athlete after exercise can each be estimated with reasonable precision, given the known and predictable qualities of the components involved. Psychological recovery from exercise is a true variable. Every athlete reacts in a different way to similar stresses. After prolonged and difficult periods of training, or key competitions, many athletes build short rest breaks into their program to maintain mental freshness in their approach to the sport. In some instances, the spirit of the maxim "a change is as good as a rest" is employed, when the athlete continues to train at a significant level, but in an alternate sport.