The myth of the body type classification

There’s a common belief that we all fall into one of 3 body types.

Based on the somatotype theory, devised in the 1940s by American psychologist William Herbert Sheldon, everyone in the world is either an ectomorph, mesomorph or endomorph.

Ectomorphs are defined as slender, lean and best suited to endurance activities. In contrast, endomorphs are seen as strong, larger and able to gain muscle quickly. Finally, mesomorphs are a combination of both; athletic and naturally predisposed to easily lose fat and gain muscle.

Sheldon’s theory also suggested that the size and shape of a person's body indicated their intelligence, moral worth and even future achievement.

According to Sheldon, endomorphs are outgoing and friendly but also lazy and selfish. Mesomorphs, in contrast, are popular, extroverted and tough, whereas ectomorphs are intelligent and gentle, but also self-conscious and anxious. As a supporter of eugenics, Sheldon even contended that criminals tended to be mostly mesomorphic.

Unsurprisingly, within just a few years of its publication, psychologists started to discredit Sheldon’s theory. Nevertheless, it’s still seen as the benchmark by many in the fitness community - it’s even taught in universities.

The first issue is that the system that Sheldon proposed is a huge oversimplification; we simply can't classify body types into just three classes.

Every one of the nearly eight billion people on earth has a slightly different body type based on our underlying DNA and ethnic heritage. We also inherit traits from our relatives and, at an individual level, we all have unique characteristics such as the proportion of muscle fibre types and the length of our limbs. These characteristics all combine to form unique body types.

The second issue is that your body type isn’t fixed. Our bodies change and evolve over time, based on our lifestyle and eating habits, training methods, frequency, and intensity. Endurance activities like running and HIIT, for example, train the slow twitch muscle fibres, helping to develop lean muscle mass. Strength training, in contrast, builds fast-twitch and intermediate muscle fibres, which increases muscle size.

And the third issue - by restricting us to predetermined fixed body types, we limit the perception of what we can achieve.

Someone considered an ectomorph might think that it’s impossible for them to ever gain strength, so they never even bother trying. An endomorph could believe that they can't lose weight, when, with a few lifestyle changes, there’s no reason why they couldn’t.

Whilst it’s true that we each ‘tend’ towards a particular body type, individual differences play a far more important role and a combination of several factors determine our body type, not an anachronistic and largely debunked theory.