Man takes exercise, but not very well (5)

I believe the answer is:

ropey

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'not very well' is the definition.
Both the answer and definition are adjectives. Maybe there's a link between them I don't understand?

'man takes exercise' is the wordplay.
'man' becomes 'roy' (I've seen this before).
'takes' indicates putting letters inside.
'exercise' becomes 'pe' (Physical Education).
'roy' going around 'pe' is 'ROPEY'.

'but' is the link.

Can you help me to learn more?

(Another definition for ropey that I've seen is " Very poor quality".)

I've seen this clue in The Daily Express.

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