Ectomorphic refers to a body type characterized by a slim, lean physique with narrow shoulders and hips. Individuals with this body type typically have a fast metabolism, making it difficult for them to gain weight or muscle mass. Ectomorphs often have long limbs and little body fat, which can give them a delicate appearance. This classification is part of the somatotype theory developed by William Sheldon in the 1940s. The three primary body types are ectomorphic, mesomorphic, and endomorphic. Understanding these body types can help individuals tailor their fitness and nutrition plans to achieve their health and fitness goals.