INJURED WAS REMOVING A SPROCKET FROM THE SHAFT OF AN APRON FEEDER TO FACILITATE THE CHANGING OF THE SHAFTS BEARING, INJURED HIS LOWER BACK. HE WAS IN A BENT OVER POSITION AND WHILE REMOVING A HEAVY SPROCKET FROM THE SHAFT, TWISTED TO THE SIDE. HE REPORTEDLY FELT A SHARP PAIN IN HIS LOWER BACK WHILE PERFORMING THIS ACTIVITY.