Suitable for a bit of a stiff back (3)
I believe the answer is:
fit
'suitable' is the definition.
(similar in meaning)
'bit of a stiff back' is the wordplay.
'bit of' indicates a hidden word.
'back' says the letters should be written backwards.
'tif' is hidden in the letters of 'stiff'.
'tif' reversed gives 'FIT'.
'for a' is the link.
(Other definitions for fit that I've seen before include "Certified OK by the doctor" , "Adapt; well" , "Healthy; conform to" , "Suitable; healthy" , "Strong" .)