Be keen, loosen up then exercise (7)

I believe the answer is:

enthuse

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'be keen loosen' is the definition.
I can't judge whether this definition defines the answer.

'up then exercise' is the wordplay.
'up' indicates anagramming the letters.
'exercise' becomes 'use' ('use' can be a synonym of 'exercise'**).
'then' anagrammed gives 'enth'.
'enth'+'use'='ENTHUSE'

Can you help me to learn more?

(Other definitions for enthuse that I've seen before include "Fill with keenness" , "Cheer" , "Seem keen" , "Gush in praise" , "Show great interest" .)

I've seen this clue in The Telegraph.

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