Particular relaxation around muscle (7)
I believe the answer is:
respect
'particular' is the definition.
(both can mean a detail or matter for consideration)
'relaxation around muscle' is the wordplay.
'relaxation' becomes 'rest' (synonyms).
'around' indicates putting letters inside.
'muscle' becomes 'pec' (pectoral muscle).
'rest' going around 'pec' is 'RESPECT'.
(Other definitions for respect that I've seen before include "Deference, obedience" , "Point" , "Treat with care, deference" , "Observe" , "Venerate" .)