What could make one sexier? Rec fitness equipment (9)
I believe the answer is:
exerciser
'fitness equipment' is the definition.
(equipment or apparatus used for exercise)
'what could make one sexier? rec' is the wordplay.
'what could make' indicates anagramming the letters.
'sexier'+'rec'='sexierrec'
'sexierrec' is an anagram of 'EXERCISER'.
(Other definitions for exerciser that I've seen before include "Person working out" , "I work out" , "Device helping strengthen muscles" , "Fitness fanatic" , "One keeping fit" .)