Crossword Genius

Run until the normal working temperature is reached (4,2)

Ross

I think it could be either:

Which length description are you looking for?:

6

4,2

warm up

(Other definitions for warm up that I've seen before include "Athletes do it" , "Exercises needed before running" , "Exercise before race - reheat food - become more animated" , "Rehearse" , "heat" .)

I've seen this clue in The Guardian.
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