A PIECE OF 1/4"" MILD STEEL PLATE 32""X 60"" WAS BEING LOADED ONTO A WELDING VEHICLE. THE STEEL WEIGHED APPROX. 136 LBS. THE PLATE WAS LIFTED UP & LEANED AGAINST THE VEHICLE. EE PICKED UP THE EDG E THAT WAS AGAINST THE FLOOR TO SLIDE IT ONTO THE VEHICLE & HE FELT A SMALL TWINGE IN HIS BACK.