Optimize, not maximize. That phrase might be the key to finding the ideal level of hydration for summer running. And while scientific research into hydration is sophisticated and complex, finding the right amount—and the right kind—of liquid to keep you running safely when the temperature rises doesn’t have to be.
Dehydration, Hydration, and Hyperhydration
Dehydration occurs when the amount of water lost is not replaced in a timely manner. Mild dehydration can result in symptoms that more unpleasant than truly life-threatening, such as a dry mouth, sleepiness, or a headache. But very quickly, dehydration can result in symptoms that are more serious and should not be ignored. According to the Mayo Clinic, the following symptoms warrant medical attention:
• Extreme thirst
• Irritability and confusion in adults
• Very dry mouth, skin and mucous membranes
• Lack of sweating
• Little or no urination — any urine that is produced will be dark yellow or amber
• Sunken eyes
• Shriveled and dry skin that lacks elasticity and doesn’t “bounce back” when pinched into a fold
• Low blood pressure
• Rapid heartbeat
• In the most serious cases, delirium or unconsciousness
Under normal conditions, the average adult loses approximately 10 cups (2.5 liters) of water every day. For most of us, this loss of water from sweating, exhaling, and excreting waste causes us to feel thirsty, and we replenish with liquids, at a rate that allows the body to absorb fluids efficiently.
But for athletes, especially those who engage in endurance events, train at high altitudes, or exercise in warm, humid conditions, replacing lost fluids becomes much more difficult due to several factors.
Length of exercise
According to the Mayo Clinic, endurance athletes are at an increased risk of dehydration because staying properly hydrated becomes more challenging over time. The body can absorb somewhere between 24 and 32 ounces of fluid an hour, about half the amount that you can lose while exercising in high temperatures, so even if you are consuming liquid as you exercise, you accumulate what the Mayo Clinic calls a fluid debt . For those who limit themselves to training or exercise sessions of an hour or less, this debt will be minimal, but with each hour of exercise, the risk of dehydration increases.
Dehydration can also occur over several days with even moderate exercise if you don’t replace your daily water loss.
Most of us would probably recognize the risks associated with running in triple digit temperatures, but dehydration and other heat-related illnesses can happen at lower temperatures than might be expected. The American College of Sports Medicine found that the risks associated with exercising in warm weather start to increase when the temperature rises about 68 degrees.
As tempting as it might be to head off dehydration by consuming as much liquid as possible before, during, and after exercise, over hydrating (called hyperhydration) is just as risky as dehydration. When you consume too much liquid too quickly, sodium levels in the body can drop. A small drop in sodium levels can cause headache, vomiting, and swollen hands and feet, but more pronounced sodium deficiencies could be fatal.
The key to avoiding dehydration is simple—minimize the fluids your body loses during exercise. In order to do that, you need to know the rate of fluid loss during exercise and then consume that amount before, during, and after you run. The American College of Sports Medicine suggests a simple way to determine your rate of water loss due to sweating and exhaling during exercise:
• First weigh yourself in the morning, before eating or drinking but after you urinate for the first time. To increase accuracy, establish a baseline weight by stepping on the scale three days in a row (for men) and seven days in a row for women (to account for monthly fluctuations in body weight).
• After completing a run, weigh yourself as soon as possible. If you can remove all or most of your sweat-soaked clothing to do this, the results will be more accurate. The difference in your baseline body weight and your post-run body weight represents the amount of fluid you lost during exercise.
• If you consumed any liquids during your run or immediately after, your weight loss will be increased by the amount of liquid you consume. So, for example, if the difference between your baseline and post-run weight was 1.5 pounds and you drank 16 ounces of fluid during your run, your total weight loss due to sweating and exhaling was 2.5 pounds, and to replace that fluid, you would need to consume a total of 40 ounces of fluid.
Generally, fluid loss of less than 2% of body weight, or less than one pound for every 50 pounds of body weight, suggests that an athlete is an efficient hydrator; that is, she consumes liquid at about the right amount to replace that lost during exercise. Water loss greater than 2% begins to result in a decrease in athletic performance, and losses of greater than 3% will often lead to symptoms such as disorientation, headaches and dizziness.
What to drink?
Pre-run hydration is meant to provide the body with some of the water that will be lost during exercise, and assuming that you are not already suffering from dehydration, either water or a sports drink is sufficient. If your run is planned to last more than 45 minutes or so, you should consume 17-20 oz. of fluid 2-3 hours before running and 10-12 oz. of water or sports drink 10 minutes before running.
According to Dr. Douglas J. Casa of the Human Performance Laboratory at the University of Connecticut, post-run hydration should include water, carbohydrates, and electrolytes and should be consumed within two hours of running, especially if the run was longer than 45 minutes or was particularly intense.