Physical exercise
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# Overview
Physical exercise is manual activity that develops or maintains physical fitness and overall health. It is often practiced to strengthen muscles and the cardiovascular system, and to hone athletic skills. Frequent and regular physical exercise boosts the immune system, and helps prevent   diseases of affluence such as heart disease, cardiovascular disease, Type 2 diabetes and obesity. It is also improves mental health and helps prevent depression.

# 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, walking, running, hiking, and playing tennis focus on increasing cardiovascular endurance.
- Anaerobic exercises such as weight training, functional training or sprinting increase short-term muscle strength.

# Exercise benefits
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.
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 of aerobic exercises. Exercise can also increase energy and raise one's threshold for pain.
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 (aka endorphins, a naturally occurring opiate that in conjunction with other neurotransmitters is responsible for exercise induced euphoria and has 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. 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, see Organ hypertrophy).
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.

## Steps per day and mortality benefit
Walking is associated with reduced mortality.

# Common myths
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 in a reasonable state of fitness for that particular activity. A doctor should always be consulted before any radical changes are made to a person's current exercise regimen. 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 caveat is that heavy weight training in adolescents can damage the epiphyseal plate of long bones.

## Targeted fat reduction
Spot reduction is a myth that exercise and training a particular body part will preferentially shed the fat on that part; for example, that doing sit-ups is the most direct way to reduce subcutaneous belly fat. This is false: 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. There is a very slight increase in the fat burnt at the area being exercised (e.g Abs) compared with the rest of the body, due to the extra blood flow at this area.

## Muscle and fat tissue
Some people incorrectly believe 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 "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 to 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 what existed before exercising. The results are all the training effects of regularly exercise - increased muscular strength, endurance, bone density and connective tissue toughness.
Too much exercise can be harmful. The body part exercised needs 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.
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.
Exercise-associated hyponatremia (EAH), is not uncommon. Researchers found, for instance, that 13% of the athletes who finished the 2002 Boston Marathon were in a clinically hyponatremic condition.
Too much exercise can also cause a female to miss her period, a symptom known as amenorrhea.

# Nutrition and recovery
Proper nutrition is at least as important to health as exercise. When exercising it becomes even more important to have good diet to ensure the body has the correct ratio of macronutrients whilst providing ample micronutrients, this is 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.
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
- increasing chemicals in the brain such as dopamine, glutamate, norepinephrine and serotonin that help cognition

# 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.

# Breathing
Active exhalation during physical exercise helps the body to increase its maximum lung capacity, and oxygen uptake. This results in greater cardiac 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 lung efficiency.

# Tactics to increase physical activity by individuals
Physical activity monitors that provide feedback to the wearer can increase activity.