Check pace, needing oxygen to replace energy (4)
I believe the answer is:
stop
'check' is the definition.
('stop' can be a synonym of 'check')
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for stop that I've seen before include "Put an end to" , "Knock out" , "End - period" , "Go no further" , "break" .)