Support twisted bone that's restricting energy (4)
I believe the answer is:
bier
'support' is the definition.
(bier is a kind of support)
'twisted bone that's restricting energy' is the wordplay.
'twisted' is a reversal indicator.
'bone' becomes 'rib' (rib is a type of bone).
'that's restricting' means one lot of letters goes inside another.
'energy' becomes 'e' (physics symbol as in E=mc2).
'rib' placed around 'e' is 'reib'.
'reib' reversed gives 'BIER'.
(Other definitions for bier that I've seen before include "Corpse carrier" , "Og high standing" , "Support for a coffin before burial" , "It takes a stiff" , "One supports stiff" .)