The i/e was part of a 3 man crew installing handrails @ the barge loadout. 2 employees were moving by hand, 2 @ a time, 1"" steel bars to be used as the horizontal part of the handrail, to an area where the uprights were already installed. The i/e reported that he bent over @ the waist to pick up 1 end of 2 bars and felt a pull in his back as he was straightening up.