EE WAS ASKED TO DRIVE & DUMP 2 HAUL TRUCKS THAT HADN'T BEEN UNLOADED FROM PREV. SHIFT. AS HE WAS DISMOUNTING THE 1ST HAUL TRUCK, HE FELT A SLIGHT PAIN IN HIS LOWER BACK. WAS UNABLE TO CLIMB ALL THE WAY UP THE LADDER OF THE 2ND HAUL TRUCK - REALIZED HE HAD PULLED A MUSCLE IN HIS LOWER BACK. PHYSICIAN DIAG.: INFLAMMATION RELATED TO A CHRONIC TYPE COND. GIVEN SHOT & PRESCRIPTION.