TWO MECHANICS WERE ASSIGNED TO CHANGE THE WEST SIDE LINE #1 PELLETIZING FURNACE COUNTERWEIGHT CABLE. PART OF THE JOB INVOLVED MANUALLY LIFTING A 70# (6 TON) CHAIN HOIST. ONE MECHANIC EXPERIENC ED A BACK STRAIN. THIS WAS RECENTLY DETERMINED TO BE REPORTABLE AS A NEW INCIDENT, BASED ON THE RECEIPT OF MEDICAL DOCUMENTATION.