I got an email from Active Triathlete this morning... and followed one of the links to read this interesting information on cramping during workouts as it relates to sodium intake:

Athletes who look like they've been rolling around in the salt flats of Utah every time they finish a workout suffer huge sodium losses. Studies have shown that "salt-cakers" like yourself are much more prone to muscle cramps during exercise (Bergeron, 2000). On the issue of muscle fatigue, I'm not sure of your level of conditioning, but I do know that a 20-mile outing will cause fatigue in most people's calves. I sure know it would in mine. When a person’s calves are firing stride after stride for hours on end, and that person also suffers a sodium loss, the stage is set for muscle cramping.

The role of sodium
Sodium is an important element in initiating signals from nerves that lead to movement in the muscles. A sodium deficit makes muscles "irritable," and with just the slightest stress that deficit may cause the muscle to contract and twitch uncontrollably. For many years, athletes attributed cramping to depletion of potassium or other minerals like calcium and magnesium. However, recent studies have shown that the amount of these elements lost through sweat is minimal (Horswill, 2000). Sodium loss is the true culprit in muscle cramping.

The question that spawned the article was from someone who was doing a 20 mile run in preparation for a marathon. While my running distance is not near that, I do know that I sweat saltier than the average person. I've within the last 6 months started using Accelerate during long training rides. It's a powder you mix into water which is similar to Gatorade, but has some extra stuff in it like whey proteins. I also like it better than Gatorade because I can drink it easier than Gatorade (which always seemed strong to me). If you sweat a lot, and are training hard, water just isn't enough.