The most common and most likely answer to this crossword clue is the 9 letter word RETRACTOR
I've seen this crossword clue in The Guardian
R
E
T
R
A
C
T
O
R
More clues leading to the result RETRACTOR
- Muscle shown by minister containing scheming from the right
- Muscle that’s required on farm vehicle
- Extremely reliable vehicle – one holding things back?
- Perform in terror, twanging muscle
- Muscle 19 down turned to right
- Muscle resistance seen in retired player
- Instrument of terror deployed to limit parliamentary bill
- Theatre item about origins of Troy resonates with performer
- Instrument from store regularly found in nuclear facility
- Retired player, after run, pulling muscle
Buddy explains!

The straight part
We know that "muscle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case muscle = retractor.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 RETRACTOR mean?
RETRACTOR noun- One who, or that which, retracts.
- In breech-loading firearms, a device for withdrawing a cartridge shell from the barrel.
- A chess puzzle in which a number of moves are retracted and the solver is challenged to reach an alternate outcome.
- A surgical instrument used to hold apart the edges of an incision or wound.
- A bandage to protect soft parts of the body from injury by a surgical saw.
- A muscle serving to draw in any part.