Admire muscle in others (7)
I believe the answer is:
respect
'admire' is the definition.
(admire can mean to respect)
'muscle in others' is the wordplay.
'muscle' becomes 'pec' (pectoral muscle).
'in' indicates putting letters inside.
'others' becomes 'rest' (eg the rest of a group).
'pec' put inside 'rest' is 'RESPECT'.
(Other definitions for respect that I've seen before include "High opinion or regard for" , "Show deference (to)" , "Admiration or esteem" , "estimation" , "Sceptre (anag)" .)