After breather, energy to spring forward (5)
I believe the answer is:
lunge
'spring forward' is the definition.
(to lunge is to jump or dive forward)
'after breather energy' is the wordplay.
'after' is a charade indicator (letters next to each other).
'breather' becomes 'lung' (you breathe with your lungs).
'energy' becomes 'e' (physics symbol as in E=mc2).
'lung' put next to 'e' is 'LUNGE'.
'to' is the link.
(Other definitions for lunge that I've seen before include "Sudden move forwards" , "Charge" , "Stab" , "Thrust forward as in fencing" , "(Make a) forward thrust" .)