Whatever it's called requires a bit of strength in gymnastics (6)
I believe the answer is:
thingy
'whatever it's called' is the definition.
'a bit of strength in gymnastics' is the wordplay.
'a bit of' says the answer is hidden in the clue.
'THINGY' can be found hidden inside 'strength in gymnastics'.
'requires' is the link.
(Other definitions for thingy that I've seen before include "I forget his name" , "What's-its-name - nighty (anag)" , "whose name can't be remembered" .)