Physical exercise is any bodily activity that enhances or maintains physical fitness and overall health and wellness. It is performed for various reasons, including strengthening muscles and the cardiovascular system, honing athletic skills, weight loss or maintenance, and merely 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 may also help prevent depression, help to promote or maintain positive self-esteem, improve mental health generally, and can augment an individual's sex appeal or body image, which has been found to be linked with higher levels of self-esteem. Childhood obesity is a growing global concern, and physical exercise may help decrease some of the effects of childhood and adult obesity. Health care providers often call exercise the "miracle" or "wonder" drug—alluding to the wide variety of proven benefits that it can provide.
In the United Kingdom two to four hours of light activity are recommended during working hours. This includes walking and standing
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. Developing research has demonstrated that many of the benefits of exercise are mediated through the role of skeletal muscle as an endocrine organ. That is, contracting muscles release multiple substances known as myokines which promote the growth of new tissue, tissue repair, and multiple anti-inflammatory functions, which in turn reduce the risk of developing various inflammatory diseases.
Exercise reduces levels of cortisol, which causes many health problems, both physical and mental.Conversely, exercise increases levels of saliva nitrite, which can be converted to the nitric oxide, thereby, increasing intensity and training load. Saliva testing for nitric oxide serves as a marker for training status.
Endurance exercise before meals lowers blood glucose more than the same exercise after meals.According to the World Health Organization, lack of physical activity contributes to approximately 17% of heart disease and diabetes, 12% of falls in the elderly, and 10% of breast cancer and colon cancer.
There is evidence that vigorous exercise (90–95% of VO2 Max) induces a greater degree of physiological cardiac hypertrophy than moderate exercise (40 to 70% of VO2 Max), but it is unknown whether this has any effects on overall morbidity and/or mortality.Both aerobic and anaerobic exercise work to increase the mechanical efficiency of the heart by increasing cardiac volume (aerobic exercise), or myocardial thickness (strength training). Ventricular hypertrophy, the thickening of the ventricular walls, is generally beneficial and healthy if it occurs 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 can never augment endurance. However, muscle hypertrophy from resistance training is primarily determined by diet and testosterone. 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.
Cardiovascular system
The beneficial effect of exercise on the cardiovascular system is well documented. There is a direct relation between physical inactivity and cardiovascular mortality, and physical inactivity is an independent risk factor for the development of coronary artery disease. There is a dose-response relation between the amount of exercise performed from approximately 700 to 2000 kcal of energy expenditure per week and all-cause mortality and cardiovascular disease mortality in middle-aged and elderly populations. The greatest potential for reduced mortality is in the sedentary who become moderately active. Most beneficial effects of physical activity on cardiovascular disease mortality can be attained through moderate-intensity activity (40% to 60% of maximal oxygen uptake, depending on age). ... persons who modify their behavior after myocardial infarction to include regular exercise have improved rates of survival. ... Persons who remain sedentary have the highest risk for all-cause and cardiovascular disease mortality.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 has a beneficial effect on the human immune system; 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 infection occurrence. However, 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 and nonathletes are generally similar. Athletes may have slightly elevated natural killer cell count and cytolytic action, but these are unlikely to be clinically significant.
Vitamin C supplementation has been associated with lower incidence of URTIs in marathon runners.
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. In individuals with heart disease, exercise interventions lower blood levels of fibrinogen and C-reactive protein, an important cardiovascular risk marker.The depression in the immune system following acute bouts of exercise may be one of the mechanisms for this anti-inflammatory effect.
Cancer
A systematic review evaluated 45 studies that examined the relationship between physical activity and cancer survivorship. According to the study results "There was consistent evidence from 27 observational studies that physical activity is associated with reduced all-cause, breast cancer–specific, and colon cancer–specific mortality".
Epigenetic effects
Physical exercise was correlated with a lower methylation frequency of two tumor suppressor genes, CACNA2D3 and L3MBTL.[30][31] Hypermethylation of CACNA2D3 is associated with gastric cancer, while hypermethylation of L3MBTL is associated with breast cancer, brain tumors and hematological malignancies.[30][31][32][33] A recent study proposed that "DNA methylation may be a mechanism linking exercise and cancer incidence and could serve as a biomarker for behavioral intervention trials. Studies with larger samples, objectively measured exercise, and more cancer-related markers are needed". According to the study, "Individuals who were more physically fit and who exercised more minutes per week had lower levels of DNA methylation. Those who increased their minutes of physical activity over 12 months experienced decreases in DNA methylation."
Cancer cachexia
Physical exercise is becoming a widely accepted non-pharmacological intervention for the prevention and attenuation of cancer cachexia. "Cachexia is a multiorganic syndrome associated with cancer, characterized by inflammation, body weight loss (at least 5%) and muscle and adipose tissue wasting". The exercise-induced transcription coactivator peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α) (see PPARGC1A), which suppresses FOXO and NF-κB dependent transcription during atrophy induced by fasting or denervation, may be a key intermediate responsible for the benficial antiatrophic effects of physical exercise on cancer cachexia.[37][38] The exercise-induced isoform PGC1α4, which can repress myostatin and induce IGF1 and hypertrophy, is a potential drug target for treatment of cancer cachexia.[39] Other factors, such as JUNB and SIRT1, that maintain skeletal muscle mass and promote hypertrophy are also induced with regular physical exercise
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