EE WAS REMOVING A HOIST MOTOR COUPLING GUARD TO GREASE THE COUPLING. HE HAD TO TUG ON THE GUARD TO GET IT LOOSE. HE THEN STEPPED BACK AND TURNEDTO HIS LEFT TO SET IT DOWN. WHEN HE WENT TO STRA IGHTEN BACK UP HE FELT LOWER BACK LOCK UP & HIS LEFT LEG GO NUMB.