Wounded Hercules, losing energy, stumbles (7)
I believe the answer is:
lurches
'stumbles' is the definition.
('lurch' can be a synonym of 'stumble')
'wounded hercules losing energy' is the wordplay.
'wounded' is an anagram indicator (I've seen this in other clues).
'losing' suggests deleting specific letters.
'energy' becomes 'e' (physics symbol as in E=mc2).
'hercules' with 'e' removed is 'hrcules'.
'hrcules' with letters rearranged gives 'LURCHES'.
(Other definitions for lurches that I've seen before include "Walks with unsteady swaying motion" , "|Moves with an unsteady uneven gait" , "Moves in unsteady swaying way, staggers" .)