So our men exercised to become massive (8)
I believe the answer is:
enormous
'massive' is the definition.
(I've seen this before)
'so our men exercised' is the wordplay.
'exercised' indicates an anagram.
'so'+'our'+'men'='soourmen'
'soourmen' with letters rearranged gives 'ENORMOUS'.
'to become' acts as a link.
(Other definitions for enormous that I've seen before include "Fat" , "Tremendous, gigantic" , "Vast" , "Extraordinarily large" , "Extra-large" .)