Physical exercise is a bodily activity that develops and 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 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.

• 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 that "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 into 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.