When to be fighting fit (4)

I believe the answer is:

bout

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'fit' is the definition.
(I've seen this before)

I don't understand how the remainder of the clue works.

(Other definitions for bout that I've seen before include "Contest; illness episode" , "Wrestling contest" , "Attack (of illness)" , "Spell of eg drinking" , "wrestling match" .)

I've seen this clue in The Times and The Sunday Times.

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