muscle builder

/ˈmʌsəl ˌbɪldər/
noun
  1. A person who exercises regularly to develop large, strong muscles, especially through weightlifting.
    • As a dedicated muscle-builder, she spends two hours at the gym every day.
    • The magazine featured an interview with a famous muscle-builder from the 1980s.
    • He started as a casual runner but later became a serious muscle-builder.