Body type refers to the idea that there are three generalized body compositions that people are predetermined to have. The concept was theorized by Dr. W.H. Sheldon back in the early 1940s, naming the three somatotypes endomorph, mesomorph, and ectomorph. Mesomorph Body Type has your classic athletic body. With a larger bone structure and average metabolism, they can build definition and gain muscle pretty easily. Mesomorphs are typically thought of because the luckiest of those 3 body types – given their ability to create muscle without putting on an excessive amount of excess fat.