Metal in barbells (4)
I believe the answer is:
iron
'metal in barbells' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for iron that I've seen before include "Metallic element, symbol Fe" , "See 14" , "Hard metal" , "Box-shaped instrument of torture -- no meridian (anag)" , "Strong metal; golf club" .)