OPERATOR REPORTED HIS BACK STARTING HURTING WHILE HE WAS OPERATING BACK HOE LOADING OFF ROAD TRUCKS IN HARD PAN. OPERATOR CONTINUED TO LOAD TRUCKS UNTIL THE END OF HIS SHIFT. AT THIS TIME, OPE RATOR COULD HARDLY EXIT EQUIPMENT. WITH ASSISTANCE OF SUPERVISOR, OPERATOR EXITED EQUIPMENT AND WAS TAKEN FOR MEDICAL TREATMENT.