Luke Hoffman, author of the HSW article entitled How Aspirin Works, offers the following thoughts on muscle cramping:
"First, since there is so little good research on cramps, a lot of myths
have built up around the subject. So let's start with the facts. Muscle cramps are very common during
(but more commonly after) exercise. There have been several theories
about why they happen, including low blood sugar, dehydration, salt
imbalances after sweating, and either extreme heat or cold. All of these
are known to cause cramping by themselves, but it's unclear if any are the
culprit with normal exercise-induced cramps.
According to current theory
in the sports science literature (as of 1997), skeletal muscle cramps
during exercise probably happen when muscles that are shortened (for
example, a calf muscle when your toe is pointed) are repeatedly
stimulated. This can happen if your foot is extended, toe pointed, and you
keep extending it further. You can actively do this by, for example, running on your
toes or doing lots of toe-raises without going down to extend the muscle. What appears to
happen is that the muscle gets fatigued, and it doesn't relax well. There
is a reflex arc, made up of the muscle, nerves carrying signals to the
central nervous system (CNS), and nerves carrying signals from the CNS
back to the muscle, and this arc keeps carrying signals through it from
and to the muscle that keep it contracted. This appears to lead to a
sustained contraction in the muscle, also known as a cramp.
Stretching (in this case,
grabbing your toe and stretching the calf) is about the only thing that
breaks this reflex arc signal and stops the cramp when it comes to
exercise-induced cases. But the muscle is still fatigued, and the cramp
process is easy to re-trigger until the muscle rests for a while. The
fatigue-cramp process seems to happen most often in muscles that cross two
joints, such as the calf (knee and ankle), since the muscle is easy to
shorten and continue contracting.
There are other reasons for cramps,
such as deficiency of potassium, calcium, and cold, but these are
probably not the reason for common exercise-induced cramps."
Here are several helpful links: