Walk to cut energy (4)
I believe the answer is:
lope
'walk' is the definition.
'cut energy' is the wordplay.
'cut' becomes 'lop' (lopping is a kind of cutting).
'energy' becomes 'e' (physics symbol as in E=mco).
'lop'+'e'='LOPE'
'to' acts as a link.
(Other definitions for lope that I've seen before include "Walk with long strides" , "Stride along" , "Run with long bounding steps" , "Move with a long bounding stride" , "run gently" .)