If you’ve been a runner longer than a week, then you’ve probably read the following statement at least once, if not dozens of times: “As little as 2 percent dehydration will have a negative effect on your performance.” But if this is true, then how can it also be true that, as we saw in Chapter 4, the typical winner of a major marathon is nearly 9 percent dehydrated at the finish line and is still running as fast as he was in the first mile?
The apparent contradiction between these two facts arises from the format of the studies upon which the claim that 2 percent dehydration hurts performance is based. In these studies dehydration is induced through passive heat exposure prior to a bout of exercise. When a person begins an exercise test 2 percent dehydrated or more, a negative effect on performance is seen compared to when the same person starts the same test fully hydrated. Things are different, however, when a person begins an exercise test fully hydrated and gradually becomes 2 percent dehydrated or more as a result of drinking less fluid than is lost through perspiration. In these cases, as we have seen, dehydration has no effect on performance as long as the person drinks enough to satisfy his or her thirst.
In short, the often-cited “2 percent dehydration” claim is misleading. But it does make the valuable point that it is important not to be already dehydrated when you begin exercise—especially when that exercise is a marathon or half marathon. One of the important objectives of prerace nutrition therefore is ensuring that this doesn’t happen.
Few runners start marathons and half marathons in a state of 2 percent dehydration, or even 1 percent. In fact, many runners are overzealous in their prerace hydrations habits. They attempt to “load up” on fluid, drinking much more than they normally do, in the hope that attaining a state of maximal hydration before the race start will minimize the effects of dehydration on their performance in the final miles of the race. This is not a practice that runners have come up with on their own; rather, it is one that they have been taught by coaches and sports nutritionists, some of whom even invoke the famous “pee rule.” The running blogger Dave Munger has observed, “One piece of advice I’ve heard given to marathoners is that you should pre-hydrate as much as possible before a race: According to this line of reasoning, the more you pee, the better you’ll do, and make sure you’ve had enough that your urine stream is completely clear.”
What the runners receiving this advice usually don’t know is that it is part of a sports-drink marketing program. Many of the coaches and nutritionists who encourage runners to “prehydrate as much as possible” before races received their own education on preexercise hydration from sources such as the 1996 position statement on exercise and hydration authored by the American College of Sports Medicine. The ACSM is the world’s largest and most respected exercise science institution. At the time when this position statement was published, the ACSM was backed by two “Platinum Level” corporate sponsors: Gatorade and the Gatorade Sports Science Institute.
The mere fact that the advice to load up on fluid before races comes through an interested party does not guarantee that it is bad advice—but, in fact, it is bad advice. We have seen that the only thing you’re likely to accomplish by drinking as much as possible during races is to increase your risk for GI distress. Similarly, the only thing you’ll accomplish by drinking excessively before a race is to increase the number of bathroom trips you need to make before and during the race. Humans are not camels. Our body has minimal capacity to store extra fluid. Any fluid you take in beyond the amount that is required to attain euhydration (normal hydration) will go straight to your bladder. Unless you have allowed yourself to become severely dehydrated over the course of the day and night before your race, you will not need much fluid to attain euhydration on race morning. Twelve to 16 ounces consumed between the time you wake up and one hour before the start of your race should do the trick. If you urinate at least once after your initial visit to the bathroom upon waking up, consider your mission accomplished.
Tim Noakes, author of Waterlogged: The Serious Problem of Overhydration in Endurance Sports, advises athletes to stop drinking two hours before the start of a race. I prefer to wait until one hour prior to the gun to stop drinking. I find the two-hour cutoff to be impractical, as I’m often just waking up two hours before race time, and as long as I don’t drink too much before, the one-hour cutoff suffices to eliminate the need for midrace bathroom breaks. Many runners who don’t realize that they are not camels continue to drink until minutes before the race begins, a behavior that makes about as much sense as drinking a liter of water just before setting out on a long drive toward a destination you’re in a hurry to reach.
You can use just about anything you want to hydrate on race morning: water, juice, a sports drink, or some sort of liquid meal. The only bad choices are alcoholic beverages, for obvious reasons, and caffeinated drinks, because they’re diuretic and because pure caffeine pills are the best source of prerace caffeine. (I’ll talk more about caffeine and caffeine pills in a bit.)