Muscle injury (6)
I believe the answer is:
strain
'muscle injury' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for strain that I've seen before include "Pass through a filter" , "Melody; filter" , "Tension on trains" , "Muscle injury, put liquid through sieve" , "Distinct breed (of animal); overexert" .)