Apply a bra with great energy (3,2,4)

I believe the answer is:

fit to bust

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'with great energy' is the definition.
(fit to bust means with energy or enthusiasm)

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

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(Other definitions for fit to bust that I've seen before include "very excited?" , "What good bra should do" , "What correctly-selected bra will do" , "with extra energy" .)

I've seen this clue in The Daily Express.

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