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It happens like clockwork. On Friday nights before major races, a cell phone rings, and Dr. Stavros Kavouras answers. A training buddy or endurance-inclined friend is on the line, wanting some last-minute advice from the head of Arizona State University’s Hydration Science Lab.
“They’ll call me the night before a big marathon or half-Ironman, and they’ll be like, ‘Hey, I’m racing tomorrow. What should I drink?” Kavouras said, with an incredulous laugh. His answer is always the same: At this point, he can’t help very much.
“What am I going to tell them the day before?” he said. “That’s like me calling someone up and saying, Hey, I’m doing a marathon tomorrow. What kind of shoes should I wear? Then going out and buying them that day.”
The comparison is apt. Just as a wildcard pair of shoes can cause blisters and injury over the course of 26.2 miles, a last-minute hydration plan can create a whole lot of misery on race day. Hydration is a critical component of race-day success, and should be treated as such. What’s more, the details—what you need, how much you need, and when you need it—vary from person to person and even day to day. That’s why an individualized hydration plan, developed and refined over the course of a season, is critical.
“It’s something that you’re supposed to think of at the beginning of your season,” Kavouras said. “You have to try different things to figure out what sits better in your stomach, especially if we’re talking about really long events like marathons or Ironman, which last for hours and hours. You need to know how your body copes with combinations of different types of energy intake, because other than water, you need electrolytes and energy and carbohydrates. What types of fuel do you take? When do you take it? All these things, they should be something you figure out while you’re training and not the night before a big race.”
This is particularly important for people who experience significant water or electrolyte loss through sweat – people who require more fluids often can’t handle a one to one replacement ratio. But even those with comparatively smaller loss might find it hard to drink enough to keep up with their hydration needs. Multiple studies show that gastrointestinal issues like bloating, nausea, vomiting, and diarrhea are common in athletes, particularly those who engage in endurance events, and these issues often impair performance or subsequent recovery. The digestive system is sensitive to water and nutrient intake during exercise, which can leave many athletes feeling like the better option is to not upset the gut at all by avoiding intake altogether. (That’s a bad idea—studies show dehydration is also a culprit in GI distress, plus a whole different set of problems.)
The better solution is to train your gut the same way you train other systems in your body. Just like a training plan starts with low volume and intensity and builds over time, so too should an athlete build tolerance for fluid intake until it matches the amount of water and essential nutrients lost through sweat. This process, ideally, should start as soon as possible—not the night before the race.
The Keys to Training Your Body for Hydration
Know your sweat rate and sweat composition. Knowing how much you lose in various conditions—from running in hot and humid weather to cycling on windy days—can help you dial in exactly what you need to develop an individualized hydration plan. This can ensure you avoid both dehydration and also over-drinking, which, in extreme cases, can cause hyponatremia.
Start with a full tank. Most of us are at least mildly dehydrated all the time, meaning we’re going into most workouts already at a deficit. To bridge that gap, the American Council on Exercise recommends drinking 17 to 20 ounces of water two to three hours before exercise, then another eight ounces of water 20 to 30 minutes before the workout or race.
Experiment with different formulations. What’s in your drink matters—a lot. In addition to finding the right one to replace fluids and essential nutrients to meet your specific losses, you’ll want to find one that is tolerable to digest during workouts and races. Sport drinks come in three general formulations:
- Hypotonic: a lower concentration of carbohydrates and electrolytes than blood
- Isotonic: a similar concentration of carbohydrates and electrolytes than blood
- Hypertonic: a higher concentration of carbohydrates and electrolytes than blood
Consider multiple sources. Some find that getting sodium and carbohydrates from salt tabs, gels, bars, or real food makes it easier to then drink more plain water. Others find they can only tolerate fluids, not solids, during intense efforts. Experiment to find what makes your gut happy.
Up your intake in baby steps. If you normally drink 16 ounces per hour, but discover your sweat rate is 35 ounces per hour, don’t double your drinking right away. That could be an unpleasant experience. In one study, athletes who were not accustomed to drinking during exercise had a two-fold risk of developing GI symptoms compared to athletes who already established a drinking regimen. Ease into hydration by adding an ounce or two to your previous hourly intake for a few workouts, then another ounce for a few more, until you get at (or close to) your goal. This can gradually train your gut to tolerate the increased load (It can also let you know if you’ve got a threshold below your goal intake).
Aim for “good enough.” It’s OK if you can’t stomach an exact one-to-one replacement ratio of sweat to hydration, especially if you are a heavy sweater. Some of us simply aren’t able to drink fast enough to keep up with sweat losses. The goal in training your gut is to drink to stay hydrated or prevent a significant dehydration. Don’t let perfect be the enemy of good. Find out how much you can tolerate while exercising (see above advice on “baby steps”), and aim for that instead; make up the difference in the hours after the workout or race.
Refine as needed. Just like you make adjustments to your bike fit or buy a new wetsuit after a significant weight gain or loss, your hydration plan should be fluid (pun intended). It’s important to test your sweat rate during different sessions and different seasons to gauge your needs. Age, weight, and fitness level can also impact your hydration needs. Calibrate as needed, and you’ll have a foolproof drinking plan come race day.