The calf muscles are what are called slow twitch muscles which means that the calf muscles are, for the most part, made up of slow-twitch muscle fibers, fibers that are best at endurance feats. The gastrocnemius and the soleus run between the knee and the ankle.
Therefore the most common causes of obesity are overeating and physical inactivity. Ultimately, body weight is the result of genetics, metabolism, environment, behavior, and culture. 1  Genetics. 2  A person is more likely to develop obesity if one or both parents are obese. 3  Genetics also affect hormones involved in fat regulation. 4  For example, one genetic cause of obesity is leptin deficiency.
Medical problems. In some people, obesity can be traced to a medical cause, such as Prader-Willi syndrome, Cushing's syndrome and other conditions. Medical problems, such as arthritis, also can lead to decreased activity, which may result in weight gain.