Physical exercise

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, as well as for the purpose of 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, helps prevent depression, helps to promote or maintain positive self esteem, and can even augment an individual’s sex appeal or body image, which is also found to be linked with higher levels of self esteem. Childhood obesity is a growing global concern and physical exercise may help decrease the effects of childhood obesity in developed countries. Health care providers often call exercise the “miracle” or “wonder” drug – alluding to the wide variety of proven benefits that it provides.

Types of exercise

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US Marines exercising on the USS Bataan

Physical 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, skipping rope, rowing, running, hiking or playing tennis, focus on increasing cardiovascular endurance.
Anaerobic exercises, such as weight training, functional training, eccentric training or sprinting, increase short-term muscle strength.

Health effects

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 reduces levels of cortisol, which 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. 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.

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Exercise in space: Astronaut Daniel Tani, Expedition 16 flight engineer, works out at the Unity node of the International Space Station using the short bar of the Interim Resistive Exercise Device (IRED) to perform pull-ups to increase his upper body strength while in a microgravity environment

There is some evidence that vigorous exercise (90–95% of VO2 Max) is more beneficial than moderate exercise (40 to 70% of VO2 Max). Some studies have shown that vigorous exercise executed by healthy individuals can 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), increase testosterone and growth hormone, effects that are not as fully realized with moderate exercise. More recent research indicates that anandamide may play a greater role than endorphins in “runner’s high”. However, training at this intensity for long periods of time, or without proper warmup beforehand and cooldown afterwards, can lead to an increased risk of injury and overtraining.
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). 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 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.

Depression

A number of factors may contribute to depression including being overweight, low self esteem, stress, and anxiety. Endorphins act as a natural pain reliever and antidepressant in the body. Endorphins have long been regarded as responsible for what is known as “runner’s high”, a euphoric feeling a person receives from intense physical exertion. However, recent research indicates that anandamide may possibly play a greater role than endorphins in “runner’s high”. When a person exercises, levels of both circulating serotonin and endorphins are increased. These levels are known to stay elevated even several days after exercise is discontinued, possibly contributing to improvement in mood, increased self-esteem, and weight management. Exercise alone is a potential prevention method and/or treatment for mild forms of depression. Research has also shown that when exercise is done in the presence of other people (familiar or not), it can be more effective in reducing stress than simply exercising alone.

Sleep

A 2010 review of published scientific research suggested that exercise generally improves sleep for most people, and helps sleep disorders such as insomnia. The optimum time to exercise may be 4 to 8 hours before bedtime, though exercise at any time of day is beneficial, with the possible exception of heavy exercise taken shortly before bedtime, which may disturb sleep. There is, in any case, insufficient evidence to draw detailed conclusions about the relationship between exercise and sleep.

Source and  References http://en.wikipedia.org/wiki/Physical_exercise

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