whilst there's a lot of salt/electrolyte related anecdote around and this used to appear to be backed up by some science, the physiological evidence is fairly conclusive that runners' cramps are not related to these factors. There's a good summary of the current state of the science in Tim Noakes' excellent recent book Waterlogged. The best evidence at the moment does seem to point towards myofibrillar trauma from using the muscles for activity well in excess of trained volume or specificity. There's also a good chapter about it written for a more general readership in the Runners World book The Runner's Body. So the science is with training volume and specificity to match your racing goals. And then there's the whole compression gear can of worms still to be properly opened...

P