Meaning of “muscle” - Learner’s Dictionary

muscle

noun us uk /ˈmʌsl/
BODY [ C, U ]

B2 one of many pieces of tissue in the body that are connected to bones and which produce movement by becoming longer or shorter:

aching joints and muscles
stomach/thigh muscles
I think I may have pulled (= injured) a muscle.

More examples

CONTROL [ U ]

(Definition of “muscle” from the Cambridge Learner’s Dictionary © Cambridge University Press)