On this Adorama video, pro photographer Joe McNally talks about creating a visual representation of movement in a still image.
McNally gives two different examples of shooting sports in the olympics in a way that captures the movement of the moment. The first is a pan image using a monopod. The image captures only the legs of the runner at a relatively slow shutter speed while panning the camera on the monopod. For the second image in the pool, McNally used a flash as he was running along side the swimmer and shooting constantly – this is a difficult technique and even with experience only very few images (if any) will turn out well but you can achieve some interesting results if you have the patience (and are allowed to run in the olympic pool which is typically a no-no).