Practical Guidelines Developed by the Gatorade Sports Science Institute

Endurance athletes know that proper training, recovery, nutrition, and the right race plan are all important for success. The same is true for hydration.

Proper hydration can not only improve your performance, but is essential for reducing the risk of heat illness (such as heat exhaustion and heat stroke) and hyponatremia (a dangerous condition caused by a low level of sodium in the blood).

Endurance athletes lose substantial volumes of fluid in sweat, urine, and respiration, losses that can range from 3 quarts (liters) to over 10 quarts (liters) each day. Fluid loss – particularly from sweating – varies widely among athletes, as does electrolyte loss – especially sodium. For example, some endurance athletes are light sweaters and lose relatively little fluid and electrolytes during each hour of activity. But others sweat a lot and can dehydrate quickly if their drinking does not keep pace. To add to the variation in sweat responses, your sweat loss can change dramatically from one day to another depending on the environmental conditions, your exercise intensity, your heat tolerance, your clothing and other equipment worn, and your hydration status.

Protecting your hydration status is the easiest and most important way to protect your performance. Dehydration impairs your ability to get the most from your body during training and competition. It’s impossible to adapt to dehydration and even moderate dehydration has a negative effect on performance. So, replacing lost fluids and electrolytes is an obvious way to help you get the most out of your body.

So what should you do about hydration?

The simplest advice is to drink enough during exercise to minimize dehydration (weight lost during exercise), but avoid the over-drinking (weight gain during exercise) that can increase the risk of hyponatremia.

But how much is enough? That depends on how much sweat you’re losing. You can develop a good sense of your fluid replacement needs by stepping on a scale before and after workouts. If you lose more than 2% of your body weight (e.g., 3 lb for a 150-lb athlete), increase your fluid intake the next time out. If you’ve gained any weight at all, cut back in future sessions. After some trial and error, you’ll become good at gauging your hydration needs under varying conditions.

It’s also important to ensure adequate sodium intake during periods of heavy training and in the days leading up to races, as well as on race day. Electrolyte losses – especially sodium – can be large, at times exceeding the equivalent of one teaspoon of salt lost in a two-hour workout. If you are a heavy sweater or if you finish workouts with your skin and clothes caked with white residue, your diet should contain enough salt to replace those losses. Salting your food to taste is encouraged; during training runs and on race day, favor sports drinks over water to replace some of the sodium lost in sweat.

To make sure that your hydration plans work for you, here are some tips to keep in mind …

• You’re unique, so don’t copy what others are doing. Some athletes will need less fluid than you do, while others will need more. Weighing yourself periodically before and after a workout makes it easy to fine tune your hydration needs.
  
  
• It’s wise to stay well hydrated throughout the day, but remember that you’re a human, not a camel, so don’t quaff large volumes of fluid.
  
  
• Heed the color of your urine; if it’s light yellow, like lemonade, that’s usually a sign of good hydration. Crystal-clear urine often indicates over-hydration and the need to cut back. Dark urine (like the color of apple juice) signals dehydration and the need to drink more.
  
  
• During periods of heavy training, you can help protect your hydration status by asking yourself three questions each morning: 1) Am I thirsty? 2) Is my urine dark yellow? 3) Is my body weight down more than 2% from the day before? If the answer to at least two of those questions is "yes", you are probably dehydrated and need to increase your fluid intake during the day. No need to overdo it though. An extra quart (liter) or two spread out over the day may be all you’ll need to restore hydration.
  
  
• During exercise, drink small volumes of fluid at regular intervals. Athletes who lose little sweat might only have to drink 14 oz (about 400 ml) each hour – roughly 3-4 oz (100 ml) every 15 minutes. Athletes who sweat a lot might require four or more times as much. That wide range is why it’s essential to gauge your hydration needs during training.
  
  
• You can choose to drink both water and sports drinks during exercise. Properly formulated sports drinks contain the water, carbohydrate, sodium, and other electrolytes needed to help improve your performance.
  
  
• Research shows that a carbohydrate intake of roughly 0.5 gram per pound of body weight (1 g/kg) during each hour of exercise improves performance by providing muscles with extra energy. For example, a 121-lb (55-kg) female athlete should ingest around 55 grams of carbohydrate per hour of exercise, while a 198-lb (90-kg) male athlete should ingest roughly 90 g/hour. That carbohydrate can come from sports drinks, carbohydrate gels (with sufficient water; about 16-oz water per packet of gel), or other sources of carbohydrate. There is no benefit in exceeding 0.5 grams of carbohydrate per pound per hour (1 g/kg/hour) because the body has a limited capacity to burn the carbohydrate ingested during exercise. As a means of comparison, one quart (∼ 1 liter) of Gatorade or Gatorade Endurance Formula contains 60 grams of carbohydrate.
  
  
• Be ready to alter your fluid intake based on the conditions of your workout or competition. If it’s hotter or colder than expected, adjust your fluid intake accordingly. The same is true if you find yourself working out easier or harder than expected. Lighter intensities generally mean less sweat loss and therefore less fluid should be consumed.
  
  
• After your workouts and competitions, have something to drink if you’re thirsty. There’s usually no rush to rehydrate unless you are significantly dehydrated (loss of body weight › 2%). If you did lose more than 2% of your body weight and are planning to exercise again that day or the next, plan on drinking roughly 20-24 oz for every pound (16 oz; 0.454 kg) you’ve lost. Your body needs the extra fluid to help make up for the urine you’ll lose before your next bout of exercise.
  
  
• If you feel that you have hydrated properly during the race but you’re still not feeling well (throbbing headache, nausea, upset stomach, bloated hands or feet, wheezy breathing), do not drink until after you’ve begun to urinate. If your symptoms persist, seek medical attention.