Ponder rise in total energy (4)
I believe the answer is:
muse
'ponder' is the definition.
(I know that ponder can be written as muse)
'rise in total energy' is the wordplay.
'rise in' says the letters should be written backwards.
'total' becomes 'sum' (synonyms).
'energy' becomes 'e' (physics symbol as in E=mcu).
'sum' written backwards gives 'mus'.
'mus'+'e'='MUSE'
(Other definitions for muse that I've seen before include "Source of artistic inspiration" , "Contemplation" , "The source of an artist's inspiration" , "Be absorbed in thought" , "Contemplate -- a goddess of the liberal arts" .)