Physical exercise

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U.S. Marine emerging from the swim portion of a triathlon.

Physical exercise is any bodily activity that enhances or maintains physical fitness and overall health. It is performed for many different reasons. These include strengthening muscles and the cardiovascular system, honing athletic skills, weight loss or maintenance and for enjoyment. Frequent and regular physical exercise boosts the immune system, and helps prevent the "diseases of affluence" such as heart disease, cardiovascular disease, Type 2 diabetes and obesity. It also improves mental health and helps prevent depression. Childhood obesity is a growing global concern and physical exercise may help decrease the effects of childhood obesity in developed countries.

Types of exercise

Exercises are generally grouped into three types depending on the overall effect they have on the human body:

• Flexibility exercises, such as stretching, improve the range of motion of muscles and joints.
• Aerobic exercises, such as cycling, swimming, walking, rowing, running, hiking or playing tennis, focus on increasing cardiovascular endurance.
• Anaerobic exercises, such as weight training, functional training or sprinting, increase short-term muscle strength.

Categories of physical exercise

• Aerobic exercise
• Anaerobic exercise
• Strength training
• Agility training

Sometimes the terms 'dynamic' and 'static' are used. 'Dynamic' exercises such as steady running, tend to produce a lowering of the diastolic blood pressure during exercise, due to the improved blood flow. Conversely, static exercise (such as weight-lifting) can cause the systolic pressure to rise significantly (during the exercise).

Exercise benefits

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A common elliptical training machine.

Physical exercise is important for maintaining physical fitness and can contribute positively to maintaining a healthy weight, building and maintaining healthy bone density, muscle strength, and joint mobility, promoting physiological well-being, reducing surgical risks, and strengthening the immune system.

Exercise also reduces levels of cortisol, thereby benefiting health. Cortisol is a stress hormone that builds fat in the abdominal region, making weight loss difficult. Cortisol causes many health problems, both physical and mental.

Frequent and regular aerobic exercise has been shown to help prevent or treat serious and life-threatening chronic conditions such as high blood pressure, obesity, heart disease, Type 2 diabetes, insomnia, and depression. Strength training appears to have continuous energy-burning effects that persist for about 24 hours after the training, though they do not offer the same cardiovascular benefits as aerobic exercises do.

There is conflicting evidence as to whether vigorous exercise (more than 70% of VO₂ Max) is more or less beneficial than moderate exercise (40 to 70% of VO₂ Max). Some studies have shown that vigorous exercise executed by healthy individuals can effectively increase opioid peptides (a.k.a. endorphins, naturally occurring opioids that in conjunction with other neurotransmitters are responsible for exercise-induced euphoria and have been shown to be addictive), positively influence hormone production (i.e., increase testosterone and growth hormone), benefits that are not as fully realized with moderate exercise.

Exercise has been shown to improve cognitive functioning via improvement of hippocampus-dependent spatial learning, and enhancement of synaptic plasticity and neurogenesis. In addition, physical activity has been shown to be neuroprotective in many neurodegenerative and neuromuscular diseases. For instance, it reduces the risk of developing dementia. Furthermore, anecdotal evidence suggests that frequent exercise may reverse alcohol-induced brain damage.

Physical activity is thought to have other beneficial effects related to cognition as it increases levels of nerve growth factors, which support the survival and growth of a number of neuronal cells.

Both aerobic and anaerobic exercise also work to increase the mechanical efficiency of the heart by increasing cardiac volume (aerobic exercise), or myocardial thickness (strength training). Such changes are generally beneficial and healthy if they occur in response to exercise.

Not everyone benefits equally from exercise. There is tremendous variation in individual response to training: where most people will see a moderate increase in endurance from aerobic exercise, some individuals will as much as double their oxygen uptake, while others will never get any benefit at all from the exercise. Similarly, only a minority of people will show significant muscle growth after prolonged weight training, while a larger fraction experience improvements in strength. This genetic variation in improvement from training is one of the key physiological differences between elite athletes and the larger population. Studies have shown that exercising in middle age leads to better physical ability later in life.

Common misconceptions

Many myths have arisen surrounding exercise, some of which have a basis in reality, and some which are completely false. Myths include:

• That excessive exercise can cause immediate death. Death by exercise has some small basis in fact. Water intoxication can result from prolific sweating (producing electrolyte losses) combined with consumption of large amounts of plain water and insufficient replenishment of electrolytes, especially salt and potassium (e.g. when running a marathon). It is also possible to die from a heart attack or similar affliction if overly intense exercise is performed by someone who is not at an appropriate level of fitness for that particular activity. A doctor should always be consulted before any radical changes are made to a person's current exercise routine. Rhabdomyolysis is also a risk. Other common dangers may occur from extreme overheating or aggravation of a physical defect, such as a thrombosis or aneurysm.
• That weightlifting makes you short or stops growth. One highly debated caveat is that heavy weight training in adolescents can damage the epiphyseal plate of long bones. Template:Fact

Targeted fat reduction

Spot reduction is a myth that consists in believing that exercising and training a particular body part will preferentially shed the fat on that part. For example, doing sit-ups is not the best way to reduce subcutaneous belly fat. One cannot reduce fat from one area of the body to the exclusion of others. Most of the energy derived from fat gets to the muscle through the bloodstream and reduces stored fat in the entire body, from the last place where fat was deposited. Sit-ups may improve the size and shape of abdominal muscles but will not specifically target belly fat for loss. Such exercise might help reduce overall body fat and shrink the size of fat cells.

Muscle and fat tissue

One misconception is that muscle tissue will turn into fat tissue once a person stops exercising. This is not literally true — fat tissue and muscle tissue are fundamentally different — but the common expression that "muscle will turn to fat" is truthful in the sense that catabolism of muscle fibers for energy can result in excess glucose being stored as fat. Moreover, the composition of a body part can change toward less muscle and more fat, so that a cross-section of the upper-arm for example, will have a greater area corresponding to fat and a smaller area corresponding to muscle. This is not muscle "turning into fat" however — it is simply a combination of muscle atrophy and increased fat storage in different tissues of the same body part. Another element of increased fatty deposits is that of diet, as most trainees will not significantly reduce their diet in order to compensate for the lack of exercise/activity.

Excessive exercise

Exercise is a stressor and the stresses of exercise have a catabolic effect on the body - contractile proteins within muscles are consumed for energy, carbohydrates and fats are similarly consumed and connective tissues are stressed and can form micro-tears. However, given adequate nutrition and sufficient rest to avoid overtraining, the body's reaction to this stimulus is to adapt and replete tissues at a higher level than that existing before exercising. The results are all the training effects of regular exercise: increased muscular strength, endurance, bone density, and connective tissue toughness.

Too much exercise can be harmful. The body parts exercised need at least a day of rest, which is why some health experts say one should exercise every other day or 3 times a week. Without proper rest, the chance of stroke or other circulation problems increases, and muscle tissue may develop slowly. It has also been noted by the medical field that expectant mothers should never exercise two days consecutively.

Inappropriate exercise can do more harm than good, with the definition of "inappropriate" varying according to the individual. For many activities, especially running, there are significant injuries that occur with poorly regimented exercise schedules. In extreme instances, over-exercising induces serious performance loss. Unaccustomed overexertion of muscles leads to rhabdomyolysis (damage to muscle) most often seen in new army recruits. Another danger is overtraining in which the intensity or volume of training exceeds the body's capacity to recover between bouts.

Stopping excessive exercise suddenly can also create a change in mood. Feelings of depression and agitation can occur when withdrawal from the natural endorphins produced by exercise occurs. Exercise should be controlled by each body's inherent limitations. While one set of joints and muscles may have the tolerance to withstand multiple marathons, another body may be damaged by 20 minutes of light jogging. This must be determined by each individual.

Too much exercise can also cause a female to miss her period, a symptom known as amenorrhea.

Exercise trends

Worldwide there has been a large shift towards less physically demanding work. This has been accompanied by increasing use of mechanized transportation, a greater prevalence of labor saving technology in the home, and less active recreational pursuits.

Nutrition and recovery

Proper nutrition is at least as important to health as exercise. When exercising, it becomes even more important to have a good diet to ensure that the body has the correct ratio of macronutrients whilst providing ample micronutrients, in order to aid the body with the recovery process following strenuous exercise.

Proper rest and recovery are also as important to health as exercise; otherwise the body exists in a permanently injured state and will not improve or adapt adequately to the exercise. Hence, it is important to remember to allow adequate recovery between exercise sessions. It is necessary to refill the glycogen stores in the skeletal muscles and liver. After exercise, there is a 30 minute window critical to muscle recovery. Before doing anything else, one should drink something for recovery. Liquids are ideal after exercise and there are several studies that show low-fat milk and chocolate milk as being effective recovery beverages because of its ideal 4:1 combination of carbohydrate and protein that fuels and replenishes our muscles the best. Branched-chain amino acids are also recommended for exercise recovery.

The above two factors can be compromised by psychological compulsions (eating disorders such as exercise bulimia, anorexia, and other bulimias), misinformation, a lack of organization, or a lack of motivation. These all lead to a decreased state of health.

Delayed onset muscle soreness can occur after any kind of exercise, particularly if the body is in an unconditioned state relative to that exercise.

Exercise and brain function

In the long term, exercise is beneficial to the brain by:

• increasing the blood and oxygen flow to the brain
• increasing growth factors that help create new nerve cells and promote synaptic plasticity
• increasing chemicals in the brain that help cognition, such as dopamine, glutamate, norepinephrine, and serotonin

A 2008 review of cognitive enrichment therapies (strategies to slow or reverse cognitive decline) concluded that "physical activity, and aerobic exercise in particular, enhances older adults’ cognitive function".

Effect on the immune system

Although there have been hundreds of studies on exercise and the immune system, there is little direct evidence on its connection to illness. Epidemiological evidence suggests that moderate exercise appears to have a beneficial effect on the human immune system while extreme exercise appears to impair it, an effect which is modeled in a J curve. Moderate exercise has been associated with a 29% decreased incidence of upper respiratory tract infections (URTI), but studies of marathon runners found that their prolonged high-intensity exercise was associated with an increased risk of an infection, although another study did not find the effect. Immune cell functions are impaired following acute sessions of prolonged, high-intensity exercise, and some studies have found that athletes are at a higher risk for infections. The immune systems of athletes anf nonathletes are generally similar. Athletes may have slightly elevated NK cell count and cytolytic action, but these are unlikely to be clinically significant.

Supplementation with the antioxidants vitamin C and E has been found to decrease the release of interleukin-6 (IL-6), which would be expected to decrease the depression of the immune system. Further, vitamin C supplementation has been associated with lower URTIs in marathon runners. However, the decreased release of IL-6 limits the anti-inflammatory effect of exercse and could limit the positive adaptation effects of exercise.

Biomarkers of inflammation such as C-reactive protein, which are associated with chronic diseases, are reduced in active individuals relative to sedentary individuals, and the positive effects of exercise may be due to its anti-inflammatory effects. The depression in the immune system following acute bouts of exercise may be one of the mechanisms for this anti-inflammatory effect.

Breathing

Active exhalation during physical exercise helps the body to increase its maximum lung capacity. This results in greater efficiency, since the heart has to do less work to oxygenate the muscles, and there is also increased muscular efficiency through greater blood flow. Consciously breathing deeply during aerobic exercise helps this development of the heart and lungs.

History

The benefits of exercise have been known since antiquity. Marcus Cicero, around 65 BC, stated: “It is exercise alone that supports the spirits, and keeps the mind in vigor.”

See also

• Active Living
• American Society of Exercise Physiologists
• Army Physical Fitness Test (APFT)
• Central governor
• Exercise equipment
• Exercise hypertension
• Exercise induced nausea
• Exercise intensity
• Exercise intolerance
• Exercise physiology
• Exercise-induced anaphylaxis
• Exercise-induced asthma
• Exergaming
• Green exercise
• Health club
• Kinesiology
• Outdoor gym
• physical fitness
• Pilates
• Sports training
• List of basic exercise topics

Sources

• Donatelle, Rebecca J. (2005). Health, The Basics, 6th, San Francisco: Pearson Education. ISBN 0-8053-2852-1. 
• Hardman, A.; Stensel, D. 2009. Physical Activity and Health: The Evidence Explained. London: Routledge ISBN 978-0-415-42198-0

Further reading

• Guidance on the promotion and creation of physical environments that support increased levels of physical activity.Physical activity and the environment.