The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

That leaves you, by default,
as the MUSCLE.
The Big Bang Theory Season 3, Episode 17

Good thinking, I'll just be the MUSCLE.
The Big Bang Theory Season 1, Episode 1

Hey! I need some MUSCLE.
Westworld Season 2, Episode 6

Enlargement of the heart MUSCLE,
or hypertrophic cardiomyopathy...
The Big Bang Theory Season 3, Episode 11

We need MUSCLE
and we need enforcers.
Breaking Bad Season 2, Episode 11