Staying Hydrated with Glycerin?!

I don't really read much on conditioning for endurance sports, as the methods are generally counterproductive for field and power sports. Since Ultimate tourneys are grueling two day (or more) affairs, though, nutrition and hydration strategies can come into play. The NY Times ran an interesting piece around a week ago where they talked about a few things, but the marathon hydration bit caught my eye (well, my teammate's eye, who pointed it out to me, thanks Matt!):

[Dr. David Martin] said that while it seemed logical to drink as much water as possible before the race—and runners try it—"it doesn't work." The reason, he explained, is that drinking a lot of water increases blood volume and the body responds by getting rid of it, in urine.

"What you need to do is to increase your total body fluids another way," Dr. Martin said.

He added that the legal, safe way to do it is through glycerin loading. The technique exploits the unusual properties of glycerin, a thick, gooey sugar alcohol that is sold in drugstores as a lubricant. Each molecule of glycerin absorbs three molecules of water. During a race, the body uses the glycerin for energy. And every time the body metabolizes a molecule of glycerin, "it unleashes three molecules of water," Dr. Martin said.

The result, he said, is that "you have a water bank account."

Glycerin loading, he added, should be reserved for races of a half marathon or longer, when runners are competing in intense heat for at least an hour and a half.

That last sentence there worried me a bit. If the technique is so good, why reserve it? Why not just use it all the time? Happily, the Times ran a follow-up piece a couple days later:

Glycerin should be used with great caution, Dr. Martin says. It you use too much you can end up with excess fluid in your cells. The excess fluid in your brain can give you a headache, and excess fluid elsewhere can make you bloated. Glycerin should only be used for long runs, two hours or more, under conditions of high heat. It is useless in cooler weather. And anyone who tries it should start gradually with lower dilutions and be sure they can tolerate it before using it in a long race. That said, the formula is one tablespoon of glycerin in 36 ounces of water. You should sip it over one to two hours before you run. Dr. Martin discusses the technique in his book, "Better Training for Distance Runners," 2nd edition, published by Human Kinetics in 1997. The glycerin section is on pages 370 to 372.

I'm also curious about the rate of release of the "water bank". Marathoners never go anaerobic, right? So would a field sport athlete just burn up all the glycerin, releasing all the stored water, in short order?