The most common and most likely answer to this crossword clue is the 4 letter word PECS
P
E
C
S
Buddy explains!
The straight part
We know that "Some muscles" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case some muscles = pecs.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PECS mean?
PECS noun- (usually in the plural) The pectoralis major muscle.