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.

Exercise benefits

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. West Virginia Department of Health and Human Resources Furthermore, anecdotal evidence suggests that frequent exercise may reverse alcohol-induced brain damage.