An ectomorph is one of the three primary body types identified in somatotype theory, which categorizes human physiques. Ectomorphs typically have a slender build, with narrow shoulders and hips, and a low percentage of body fat. They often find it challenging to gain weight or muscle mass due to their fast metabolism. Individuals with an ectomorphic body type may excel in endurance sports, such as running or cycling, where a lighter frame can be advantageous. However, they may need to focus on strength training and a calorie-rich diet to build muscle effectively.