The three somatotype tendencies
Ectomorphs typically have a lean, slender build with narrow frames, lower body fat, and a tendency toward faster metabolisms. They often find it difficult to gain both muscle and body fat. Mesomorphs are characterised by an athletic, muscular build with medium frames and a broader shoulder-to-hip ratio. They tend to gain muscle more readily and maintain body composition with relative efficiency. Endomorphs naturally carry more body fat, have broader frames, and a greater tendency to store adipose tissue — particularly in the abdominal region.
Most people fall somewhere on a spectrum between types, or have a hybrid classification. A lean but muscular person might be classified as ecto-mesomorph; someone with notable muscle development but higher body fat might be endo-mesomorph. The categories are not fixed biological types but heuristic descriptions of observable body composition tendencies.