Below is the final piece of art I did for Warner Brothers-- the world's fastest man: The Flash!  I was planning to have him running so fast that he was running across water, but was a little concerned that it might be too much of a distraction down there at the bottom of the scene, so I did more like a hint at the effect instead. I think it still works good to show the speedster's motion.
See all Greg Horn's Marvel Comics art galleries at www.greghornjudge.com