The three somatotypes—endomorphic, mesomorphic, and ectomorphic Are basic classifications of animal body types according to the prominence of different basic tissues types, roughly: digestive, muscular, and nervous tissues. They form the core of a theory, developed in the 1940s by American psychologist William Sheldon, associating body types with human temperament types. This linkage is fairly simplistic and is seen as outdated in physiological science, but the account of somatotypes is still probably a valid, if limited way to sort basic body types.
Somatotype theory
Using anthropometric methods Sheldon studied the photographed bodies of some 4,000 men from front view, side view, and back view. He concluded that the physique of men can be divided into the contribution of three fundamental elements: the somatotypes. He named his somatotypes after the three germ layers of embryonic development: the endoderm that develops into the digestive tract, the mesoderm that is to become muscle, heart and blood vessels, and the ectoderm that is to form the nervous system. Sheldon’s “somatotypes” and their (presumed and supposed) associated psychological traits can be
Ectomorphic body type - is characterized by long arms and legs and a short upper body, and supposedly have a higher level of nervous tissue. They also have long and thin muscles. Ectomorphs usually have a very low fat storage; therefore they are usually referred to as skinny. An example would be an élite marathon runner.
Mesomorphic body type - is characterized by a good rate of muscle growth and a higher level of muscular tissue while maintaining a lower level of higher cognitive functions. They have large bones, solid torso combined with low fat levels. It is also noted that they have wide shoulders with a narrow waist. An example is an Olympic gymnast.
Endomorphic body type - is characterized by an increased amount of fat storage, due to having a larger amount of fat cells than the average person, as well as higher levels of digestive tissue. They have a wide waist and a large bone structure. An example is a power weight lifter.
Changing somatotypes
The three body type descriptions could be explained as differences in body composition, which can be altered by specific diets and training techniques. After a period of significant weight loss, a person who was once considered an endomorph may begin to instead resemble an ectomorph. Likewise, an athletic mesomorph may begin to look more like an endomorph as he ages and loses muscle mass.