No area of running has received more scientific exploration than the runner’s fluid needs. Literally hundreds of studies have investigated what levels of hydration will optimize your health and performance, and how dehydration can do the opposite.
Fifty years ago, health experts knew almost nothing about a runner’s fluid needs. Most road races started at noon, because that was when the Boston Marathon started. Race directors of events on July 4 didn’t seem to understand the differences between mid-April weather and July conditions. Not only that, but they never considered setting up water tables en route, and no one had ever heard of Gatorade.
Somehow we runners of that era survived. Three decades later, amazingly, the sport had changed so much that runners were more likely to be drinking too much water than too little. Sports drink companies were encouraging runners to drink as much as possible. At least that was the message many marathoners seemed to get.
Then we learned a strange new term for the first time—hyponatremia, too little sodium in the blood. This was caused by too much fluid consumption, and it caused a number of deaths in endurance events. It turned out that excessive consumption of water and sports drinks wasn’t a good thing. Less was more.
More recently, researchers, sports drink companies, and medical directors at major marathons have settled on a saner approach to hydration. Yes, runners should drink before and during marathon races and long training runs. But the drinking should be moderate.
Low-level dehydration—about 2 percent of your body weight—is no cause for alarm. In fact, it’s a normal and natural response to several hours of exercise. If you happen to weigh 150 pounds, a 2 percent dehydration represents forty-eight ounces that you do not have to drink while running.
You can gauge your level of hydration without a bathroom scale. Simply check your urine color. If it’s clear or has a straw-like tint, you’re fine. If it’s a darker yellow, you need to drink. Note: a darker color is normal in the morning when you’ve had little or nothing to drink for eight hours, and some vitamin pills and supplements can also tint the urine.
Train your gut: Many runners feel a distressed and nauseous stomach when they consume too much fluid, especially in races. However, the same runners fail to realize that they can train the gut in much the same way they train the leg muscles—little by little.
Begin by drinking slightly more than your usual amount before a workout. If that goes well, try the same procedure again, or add a bit more. Similarly, drink somewhat more while you are running. Start this process at the onset of warm weather to prepare yourself for what’s coming. A stomach that can comfortably hold more fluid will deliver more to the bloodstream, staving off dehydration.
Consume moderate amounts of water and sports drinks: Experts at the American College of Sports Medicine recommend that you drink three to six ounces every 20 minutes while running. The range is wide because your body size, your pace, the weather, and your genetics all affect how much water you need. For more precision you can conduct a simple experiment to determine your personal hydration needs.
Weigh yourself before and after a workout of measured time or distance. Be sure you are naked and dry for both weigh-ins. Ninety-five percent of the weight you’ve lost is water, not fat or muscle, so it can be considered your sweat rate. Adjust this loss to either ounces per hour or ounces per mile, whichever you find most useful. Remember that you don’t have to replace all your sweat. You simply want to keep the losses to no more than 2 percent of your body weight.
Don’t confuse dehydration and heatstroke: Many runners wrongly believe they can avoid heat illness by drinking sufficiently. But heatstroke, the most dangerous form of heat illness and a genuine threat to summer runners, is caused primarily by running too fast for the conditions.
The endurance pace you can tolerate on a hot and humid ninety-degree day is much slower than what you can run on a fifty-degree day. If you ignore this basic physiology, you risk a case of heat illness. Some races will be canceled when the conditions are too extreme. Others will turn off their timing clocks. You should do the same. You can’t beat the heat, not even with extra fluids. Be smart and run smart.