EE WAS INSTALLING A DIFFERENTIAL ON A CAT 793 OFF-HIGHWAY TRUCK. RATHER THAT USING A LADDER TO COME DOWN FROM THE TRUCK'S A-FRAME, EE JUMPED TO THE GROUND, 3-4' BELOW. WHEN EE LANDED HE FELT A SHARP PAIN IN HIS ABDOMEN. BECAME REPORTABLE ON 1/21/05 WHEN EE WENT TO DOCTOR & WAS DIAG. AS HAVING HERNIA - SURGERY SCHEDULED. PHYSICIAN'S RECOMMENDATION TO NOT RTW PRIOR TO SURG.