Produces cartoons without energy, needing upturn in sustained energy (7)
I believe the answer is:
stamina
'sustained energy' is the definition.
(I've seen this before)
'produces cartoons without energy needing upturn in' is the wordplay.
I cannot quite understand how this works, but
'in' is within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for stamina that I've seen before include "Resilience" , "Ability to maintain effort" , "energy to go on" , "resistance" , "This man owes his strength" .)