Alpha males, fit and flexible (8)
I believe the answer is:
amenable
'flexible' is the definition.
(thesaurus)
'alpha males fit' is the wordplay.
'alpha' becomes 'a' (phonetic alphabet: alpha, bravo, charlie etc.).
'males' becomes 'men' (man is a kind of male).
'fit' becomes 'able' ('able' can be similar in meaning to 'fit').
'a'+'men'+'able'='AMENABLE'
'and' is the link.
(Other definitions for amenable that I've seen before include "Nameable as being subject to the law" , "Accommodating; flexible" , "Willing to be guided or controlled" , "Pliant" , "Willing to yield or be influenced" .)