Don't get downhearted in exercise! (4,2)
I believe the answer is:
chin up
'exercise' is the definition.
(I know that chin-up is a exercise)
'don't get downhearted in' is the wordplay.
I cannot quite understand how this works, but
'in' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for chin up that I've seen before include "Stay strong" , "Keep optimistic" , "Keep smiling!" , "exercise" , "Words of encouragement in adversity" .)