muscle
「筋肉」 has another reading with different meanings.
sinewy meat
毎日運動して、筋肉を鍛えています。
I exercise every day to train my muscles.
重い荷物を持って、筋肉が痛くなった。
My muscles became sore from carrying heavy luggage.
彼は筋肉がすごくて、とても強そうです。
He has amazing muscles and looks very strong.