Answer
To be honest, I would FLIP the fashion in which you are planning on shooting. Faster subjects require faster shutter speeds. I recommend getting faster film, ISO200 would be good. If you have the option of selecting your shutter speed, and letting the camera select the FStop(Aperture) I would do that for now. Set your speed to a minimum of 1/250sec (I repeat, minimum). The higher the speed the better the stop action in the image. Another cool thing to do is to set the speed a LITTLE slower, 1/125, MAYBE 1/60, and then following (panning) your subject. Say it's a soccer player. Then AS you are following the subject, keeping him in the frame, take the shot while still panning. You'll get some really cool shots.