Potassium loading can screw you up big time, but taking a prescribed
time released dose like K Dur could be very helpful, taken with magnesium.

Susan

  No comments on potassium loading, but if you want to try vitamin B-6
and n-acetylcysteine, come back and tell us about it!

  Warning: B-6 is a diuretic and increases your need for B-2.  It's
reported to reduce cramping in pre-menstrual syndrome.  If the diuresis
is a problem, it might be better to add it to your regular diet, but
avoid it on race day.  Don't over-do it.  The DV is 2mg, but 25mg per
day surely wouldn't hurt.  When I wanted to lower my cholesterol, the
doctor recommended 50mg three times a day, and I still take 100mg once a
day, along with about 10mg of B-2.

  I don't know much about n-acetylcysteine, but it works for me.  It
helps me do more push-ups.  (Also called NAC or n-acetyl-l-cysteine.
The n- simply indicates where the acetyl group is attached.)

  Loading up on potassium may be premised on the hunch that you won't
get enough in your drinks along the way, but will get plenty of sodium,
with which it should be kept in balance.  Potassium is the main
intra-cellular, and sodium, the main extra-cellular, cation.  (They
carry positive charges and are attracted to negative electrodes, or
cathodes.)

  A swell source of potassium is Morton's Salt Substitute, but it can
be quite hard on the stomach (and heart) if you over-do it.  Best to
take it with meals or well diluted.

  One thing that web page doesn't mention may not be related to
cramping (though it may be), but is important nonetheless.  When you eat
carbohydrates, your pancreas secretes insulin, which does a number of
things to lower your blood sugar level.  For one, it ushers glucose into
your muscle *and* fat cells.  More to the point during a race, it favors
the formation of glycogen within cells and *inhibits* glycogen
breakdown.  It promotes the synthesis and *inhibits* the breakdown of
triacylglycerols in adipose tissue.

  So when you run out of glycogen (which will be fairly early in a
marathon, no matter how much you load up on carbs) and need to burn
*fat*, you certainly don't want any insulin hanging around -- and even
early in the race, you don't want it interfering with glycogen breakdown.

  Your training has probably got all these systems well tuned, but too
much insulin at the wrong time can get you into the wrong gear right
from the start, by locking up your energy stores just when you need them
the most.