Spot reduction is a myth that consists in believing 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 belly fat. 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.

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. 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.