EMPLOYEE REPORTED: HE & A CO-WORKER INSTALLED A CUTTER CLUTCH IN A CONTINUOUS MINER. DURING THIS TASK HE WAS LIFTING, PRYING & PULLING TO REMOVE THE DAMAGED PART & TO INSTALL A NEW CLUTCH. AFTER COMPLETING THE TASK PAIN & STIFFNESS WAS FELT TO HIS LOW BACK. THE CONDITION WORSENED OVER TIME, ON 9/9/04 HE RECEIVED MEDICAL TREATMENT & BEGAN MISSING SCHEDULED WORK DAYS.