Race Day Electrolyte Management
Electrolytes are an oft-overlooked aspect of race nutrition. Electrolytes are ions (sodium and potassium, among others) that your body needs for basic functioning. As you sweat during a race (even in cold weather you are sweating much more than you think!), you lose both water and electrolytes creating a state called isotonic dehydration. Therefore in order to remedy the situation, you must replace both water and electrolytes. In fact, taking in too much water without replacing your lost electrolytes can lead to hyponatremia, a potentially life-threatening disturbance which is caused by an insufficient sodium concentration in the blood.
The danger of hyponatremia is compounded by the fact that its symptoms are very similar to isotonic dehydration, the more usual form of dehydration (hyponatremia is technically a form of dehydration called hypotonic dehydration). You might experience nausea, headache, cramps, fatigue, dizziness, confusion, or fainting. These are all similar to symptoms of dehydration. However you need to be able to distinguish between the two states because you must take in both water and electrolytes to cure dehydration, but if you are hyponatremic then you need to avoid any more water intake so you don't lower your blood sodium concentration even more. One good way to distinguish between the two is to check the color of your urine. If your urine is on the clearer side, then you are more likely hyponatremic than dehydrated. Also look for swelling in your fingers and ankles which may be present if you are hyponatremic, but not if you are dehydrated.
In order to avoid hyponatremia, you must take in adequate electrolytes with your water. One of the best ways to do this is to drink an electrolyte replacement drink instead of pure water. Often these drinks have sugar in them as well which can be a great way to boost your caloric intake without having to eat as much solid food. Some racers like popular drinks like Gatorade or Powerade, but I find them too sugary for race day and they will give me an upset stomach if I am working hard. I prefer HEED which is much less sugary but still has electrolytes. I also take Endurolyte pills throughout the race to boost my electrolytes even more. There are other brands of drink mixes and pills that all claim to have the perfect blend of electrolytes but HEED and Endurolytes are the only ones I've tried and they seem to do the trick.
Note that the incidence of hyponatremia in adventure racing is probably much lower than in organized runs, triathlons, bike races, etc. This is because as an adventure racer you must carry all or most of your own water. It's much more difficult to overhydrate when you carry all your own water because you are likely to run out of water before this happens. On the other hand, during a running race you may have someone handing you a virtually unlimited supply of water at every aid station.
There's no magic formula to calculate how much you need to supplement your electrolyte intake. Over time while training and racing you will have to listen to your body. You will develop a sense for what the early stages of dehydration and hyponatremia feel like. For me, hyponatremia tends to manifest itself as a headache or lightheadedness along with a slight nausea. I can tell I'm getting fairly dehydrated by slight leg cramps and again a feeling of lightheadedness. Sometimes I even notice I'm slurring my words when it's getting worse. You'll be able to tell which is which over time by experimenting and noting what helps resolve the issue - drinking more water or taking in more electrolytes. Listen to your body. If you are extremely thirsty or have cottonmouth then you are probably at least moderately dehydrated. If you are craving salty foods then you may be hyponatremic.
Though it's hard to say exactly how many electrolyte pills to take, suffice it to say that on a hot day if you are working hard, it will be difficult to take too many! It's better to err on the side of caution here.
Eating energy bars or gels which usually contain sodium will help replace some of your electrolytes, and there are even certain brands and types of sport food that contain extra electrolytes. I've personally found that I can never maintain adequate levels of electrolytes solely through food while racing. I must take at least 2 Endurolyte pills (at a minimum) during a sprint race in order to maintain a high level of performance. In a 12 hour race I up this to about 1 pill an hour or even more if it's hot. These are extremely light and worth their weight in gold!