These body type classifications have their roots in discredited pseudoscience—but they're still common shorthand at the gym.

Ectomorphs have long, lean builds and naturally fast metabolisms that make it easier to burn body fat. However, their fast metabolism also makes building lean muscle mass harder. People with this ...

Mesomorphs were those with an even weight distribution and narrow waists, who gained muscle easily. Finally, ectomorphs were those who were tall and skinny, with long limbs, but who were naturally ...