Refuse to break sweat (5)
I believe the answer is:
waste
'refuse' is the definition.
(I've seen this before)
'break sweat' is the wordplay.
'break' indicates anagramming the letters.
'sweat' with letters rearranged gives 'WASTE'.
'to' acts as a link.
(Other definitions for waste that I've seen before include "Use carelessly" , "Become gradually weaker" , "Blow - rubbish" , "Use to no purpose" , "Spend to no purpose" .)