The ectomorph is the body type that is tall, thin, and possibly underweight — one of the three classical somatotypes, alongside the endomorph and mesomorph. Ectomorphs are characterised by a light frame, long limbs, narrow shoulders, fast metabolism, and difficulty gaining weight or muscle. The classification comes from 1940s constitutional psychology, and modern science treats it as a rough description rather than a destiny — body shape is polygenic and malleable. In sports and fitness nutrition the ectomorph is the classic “hard gainer,” advised to eat in caloric surplus with ample protein to build mass. The concept’s value is descriptive shorthand; its danger is determinism. No one is only a somatotype, but the tall, lean build it names is recognisable in every population.