WHILE WORKING ON 6 NORTH MAINS LAYING TRACK FOR 8A SECTION SWITCH, WHILE GUIDING RAIL WITH SLATE BAR HE EXPERIENCED LOW BACK PAIN. EMPLOYEE STATED THAT HE HAD PREVIOUS BACK INJURY (WHILE EMPLOYED FOR ANOTHER COMPANY) AND HAS HAD ONGOING TREATMENT. X-RAYS SHOWED NO EVIDENCE OF FRACTURE OR MALALIGNMENT.