Warms up for preliminary contests (5)
I believe the answer is:
heats
I believe this is a double definition.
'warms up' is the first definition.
(I've seen this before)
'preliminary contests' is the second definition.
(I've seen this in another clue)
'for' acts as a link.
(Other definitions for heats that I've seen before include "Eliminating rounds in a contest" , "Eliminating rounds of a race" , "Warms up for the preliminary races" , "Makes hot or warm" , "Haste (anag.)" .)