EE AND CO-WORKER WENT TO WORK ON A COAL LOADER, REPAIRING THE BACKUP ALARM. SHORTLY AFTERWARD, THEY CAME BACK TO THE WAREHOUSE AND STARTED GATHERING SUPPLIES TO PERFORM OTHER WORK. DURING THI S TIME AND WHILE EE WAS BENDING OVER TO PICK UP AN AIR HOSE, HE FELT A SHARP PAIN GO THROUGH HISLOWER BACK. HE WAS UNABLE TO SIT DOWN FOR A FEW MIN. EE RECEIVED X-RAYS AND MUSCLE RELAXERS.