Simple, cheap fluid replacement
I want to discuss electrolytes and will probably bore everyone to tears, so I'll start with the most practical thing I'll ever write: how to make your own sports drink.
Pedialyte and other similar products are made specifically for fluid replacement, but are incredibly expensive. Here's how to make exactly the same thing on the cheap. If you ever have a child who's vomiting or has diarrhea, you'll thank me for this.
In a one quart container, add 1/2 teaspoon table salt, 1/2 teaspoon baking soda, 2 tablespoons of sugar and 4 tablespoons of orange juice. The baking soda and orange juice will fizz. Then add water to fill the container. Store in the refrigerator.
Drinking on the run
Before I discuss electrolytes, I have to give practical advice on how much fluid one needs when running. I may not be the person to trust on this, as I severely dehydrated at Voyageur and Leadville last year and overhydrated at FANS.
If you're urinating every two hours and it's clear urine, you're drinking too much. If your urine is dark yellow or you haven't urinated in 5 hours, you're drinking too little. In between, it's more difficult to say. Most people can't tolerate more than a gallon of fluid in 5 hours when running, so that's a starting point for figuring out how much fluid you need in a really long run.
As to what to drink, I recommend starting with the fluid replacement drink as described above. The amount of sodium and potassium are ideal. Then, try adding increasing amounts of sugar. Eventually, you reach a point where you get thirsty during the run, no matter how much you're drinking; this means that the amount of sugar is so high that the osmolality (i.e. concentration) of the solution is keeping it from being absorbed. You want to take in as many calories from the fluid as you can, up to the point where your body can't use it - this, for me, is about 4 tablespoons of sugar per quart. So, increase the amount of sugar in small steps.
Making your own fluid replacement drink is more art than science, more trial and error than engineering. Allan Holtz has a solution that has the advantage of being fairly simple and extremely portable - the sodium and potassium levels are identical to mine: per quart, 1/2 teaspoon salt, 1/2 teaspoon Lite salt (50% table salt, 50% potassium chloride) and 1/3 cup sugar.
That's more sugar than I can tolerate, but it might be perfect for others.
Currently, my solution is, per gallon (NOT quart): 2 teaspoons salt, 2 teaspoons baking soda, 2 teaspoons citric acid (available in home brew shops), 1 teaspoon potassium chloride (salt substitute, available in grocery stores) and 9 ounces of corn syrup (not high fructose corn syrup!). I've made an average of one change per month in the recipe for the past year and a half, so it's a work in progress.
A note on S!Caps
Karl King is very knowledgable and experienced when it comes to electrolytes for ultrarunners and he is extremely helpful to those who ask questions. And he's a chemist and a homebrewer! That said, I have a problem with his product, which has ecome the standard for ultramarathons. Five (this is a correction) gel caps contain 1700 mg. of sodium and 110 mg. of potassium, the same amounts found in one liter of sweat. It's the same amount of sodium as in my replacement drink, per quart, but less potassium. If one dissolved a gel cap in a quart (or liter) of water and ate fruit during the run to replace potassium, it'd be a good idea; unfortunately, the gel cap bypasses your taste buds - you'd have trouble swallowing the salt without it - and you end up with concentrated salt in your stomach if you're not drinking enough fluid, which is often the case in ultras. This leads to nausea and vomiting. Nausea in ultras is common enough, especially in hot weather; why risk it?
The problem with my solution is that it's not something you can easily carry. It has to be mixed ahead of time, or one gets terrible gas. I've experimented with making a slurry/gel of my solution without the water. A gel cap is so simple! And Karl's making a fortune selling table salt!
Aid Station: Eugene Curnow
2 hours ago