Limber, supple (5)
I believe the answer is:
lithe
I believe this clue is a double definition.
'limber' is the first definition.
(I've seen this before)
'supple' is the second definition.
(I know that supple can be written as lithe)
(Other definitions for lithe that I've seen before include "Supple and limber" , "showing great athletic ability" , "Lissome, supple" , "Of body, flexible and supple" , "Slim and supple" .)