Rowing machine, for short (3)
I believe the answer is:
erg
'rowing machine for short' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for erg that I've seen before include "Energy expended" , "Unit of work; dunes area" , "Unit of measurement of work" , "Amount of work" , "Unit of work (phys.)" .)