LOADER OPERATOR WAS HAULING FILL STONE TO STOCKPILE AREA. HE SAID HE WAS DRIVING TOO FAST DOWN A SMALL INCLINE WHICH UPSET THE BALANCE OF THE LOADER. HE TENSED UP ON THE STEERING WHEEL AND ACC IDENTALLY SHIFTED THE LOADER INTO REVERSE. HE WAS TROWN AGAINST THE STEERING WHEEL AND THEN BACK IN THE SEAT AT AN AKWARD ANGLE, THUS STRAINING HIS BACK.