Common misconceptions
Many myths have arisen surrounding exercise, some of which have a basis in reality, and some which are completely false.
Myths include: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 at an appropriate level of fitness for that particular activity or has an undiagnosed rare condition like hypertrophic cardiomyopathy.
A doctor should always be consulted before any radical changes are made to a person's current exercise routine. 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 confirmed danger is that heavy weight training in adolescents (ages 11-16) can damage the epiphyseal plate of long bones and can stunt joints. All adolescents should refrain from any kind of strenuous weight-lifting.
Targeted fat reduction
Spot reduction is a myth that exercising and training a particular body part will preferentially shed the fat on that part.
For example, doing sit-ups is not the best way to reduce subcutaneous abdominal obesity. 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 percentage and shrink the size of fat cells.
Muscle and fat tissue
One misconception is 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. The muscle is being replaced by fat. 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.
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, and muscle tissue may develop slowly. It has also been noted by the medical field that expectant mothers should never exercise two days consecutively.
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. Another danger is overtraining in which the intensity or volume of training exceeds the body's capacity to recover between bouts.
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 for each individual.
Too much exercise can also cause a female to miss her period, a symptom known as amenorrhea
