Somatotype coined by William H. Sheldon and characterized by a lack of fat or muscle. The classic skinny person with a high metabolism, unable to gain weight through any means.

Ectomorphs are typically very thin with a flat chest and little muscle. They tend to have a delicate build and have trouble building muscle mass. Other common attributes are stooped shoulders, above average height and a young appearance. Compare with Mesomorph and Endomorph.