Shattering exercises to unwind (10)
I believe the answer is:
straighten
'unwind' is the definition.
(straightening is a kind of unwinding)
'shattering exercises' is the wordplay.
'exercises' is an anagram indicator (I've seen 'exercising' mean this).
'shattering' with letters rearranged gives 'STRAIGHTEN'.
'to' is the link.
(Other definitions for straighten that I've seen before include "Unbend, align" , "Get in line" , "put in alignment?" , "Remove bends from (something)" , "Align correctly" .)