Filled in document to maintain exercise in retirement (9)
I believe the answer is:
deputised
'filled' is the definition.
The definition and answer can be both to do with social activities as well as being past participle verbs.
Maybe there's a link between them I don't understand?
'document to maintain exercise in retirement' is the wordplay.
'document' becomes 'deed' (deed is a kind of document).
'to maintain' is an insertion indicator (maintain can mean to keep or preserve).
'exercise' becomes 'sit up' (type of exercise).
'in retirement' shows that the letters should be reversed in order (retire can mean to go back or backwards).
'deed' enclosing 'situp' is 'desituped'.
'desituped' in reverse letter order is 'DEPUTISED'.
'in' acts as a link.
Can you help me to learn more?
(Another definition for deputised that I've seen is " Stood in (for)".)