Somatotype it is not an accepted term in the dictionary of the Royal Spanish Academy (RAE ). The notion was elaborated by William Herbert Sheldon , an American psychologist who made distinctions between different kinds of bodies that, according to their characteristics, would influence people's mental faculties.

The physical types proposed by Sheldon are linked to the greater or lesser incidence of endoderm , he mesoderm and the ectoderm in the subject These three elements are the germ layers that form in embryonic development and give rise to tissues and organs .
The endoderm allows the development of the intestine; the mesoderm derives in the blood vessels, muscles and heart; and the ectoderm enables the formation of the nervous system and the skin . Sheldon defined the different somatotypes according to a score of 1 to the 7 according to the higher incidence of one or another germ layer.
Following this idea, the American psychologist established three major somatotypes: endomorphic (individuals with a tendency to accumulate fat in their body and to be overweight), mesomorphic (solid subjects and developed muscles) and ectomorphic (the people with thin body, extensive limbs and low level of body fat).
Going a little deeper into the three large groups established by the theory at hand, we can point out these other aspects:
-The endomorph is someone with a pear body, which has a wide hip and shoulders, whose head is round and that accumulates fat in areas such as thighs and arms. To all this we must add that it is considered to have a great lung capacity and that it has qualities to practice sports such as rugby or rowing.
-The mesomorph, meanwhile, is a person with narrow hips, V-shaped body, low fat and cubic head. It excels in a special way for its speed, strength and agility, so you can practice with great success physical disciplines such as long jump.
-The ectomorph, on the other hand, is characterized by having a thin, long and thin body. He does not have much muscles, his forehead is high and has both hips and narrow shoulders. These physical characteristics make him an individual who can achieve some success by performing disciplines such as gymnastics.
In addition to the above, we cannot ignore that there are certain formulas to be able to determine, in a truthful and accurate manner, to which somatotype any person belongs and for what type of sport their qualities are most optimal. Thus, for example, the ectomorph type is recommended that you practice athletics, that hockey players are mesomorphic and that trampoline gymnasts be endomorphic.
For Sheldon , somatotypes body characteristics are revealing in the development of temperament and in different psychic characteristics of Humans .
It is important to note that the theory of somatotypes had popularity in the decades of 1940 and 1950 and then it was losing validity in the scientific field. Some believe that the idea of somatotype can even be the starting point for racist positions.