Physical exercise

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A physical exercise is any bodily activity that enhances 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.^[1][2] It 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.^[3]
Aerobic exercises such as cycling, walking, running, hiking or playing tennis focus on increasing cardiovascular endurance.^[4]
Anaerobic exercises such as weight training, functional training or sprinting increase short-term muscle strength.^[5]

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 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 (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),^[6] 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.^[7] In addition, physical activity has been shown to be neuroprotective in many neurodegenerative and neuromuscular diseases.^[8] For instance, it reduces the risk of developing dementia.^[9] Furthermore, anecdotal evidence suggests that frequent exercise may reverse alcohol-induced brain damage.^[10]

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.^[11]

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.^[12][13] Similarly, only a minority of people will show significant muscle growth after prolonged weight training, while a larger fraction experience improvements in strength.^[14] This genetic variation in improvement from training is one of the key physiological differences between elite athletes and the larger population.^[15][16] Studies have shown that exercising in middle age leads to better physical ability later in life.^[17]

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,^[19] and muscle tissue may develop slowly. It has also been noted by the medical field that expectant mothers should never exercise two days consecutively.^{[citation needed]}

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.^[20] Another danger is overtraining in which the intensity or volume of training exceeds the body's capacity to recover between bouts.^[21]

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.^[22]

HEALTH