EMPLOYEE WAS HELPING INSTALL TRACK IN A GATE SECTION. HE HAD A CRESCENT WRENCH ON THE FLANGE OF A TRACK RAIL & WAS PULLING ON THE WRENCH TO TURN THE RAIL OVER. AS HE PULLED, HE FELT SOMETHING ""POP"" IN HIS BACK. THERE WAS NO DAMAGE OR IMPAIRMENT TO THE OPERATION OR EQUIPMENT. EMPLOYEE SHOULD HAVE USED A LONG BAR TO ROLL RAIL. NO OTHER FACTORS INVOLVED.