mesomorph

/ˈmɛzəˌmɔrf/
noun
  1. A person with a body type that is naturally muscular and athletic, with a medium build and low body fat.
    • Many professional swimmers are mesomorphs because their body type helps them move quickly through water.
    • The coach noticed that the new player was a natural mesomorph, with broad shoulders and strong arms.
    • She was a mesomorph, so she gained muscle easily when she started weight training.