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            How much and what should an endurance athlete drink during training and competition? The answer has varied considerably over the years.

            For example, the Oxford University rowing crew of 1860 were restricted to no more than two pints of fluid daily. In 1909, a widely read book on marathon training advised that runners should not drink during the race. “Don’t get in the habit of eating and drinking in a marathon race; some prominent runners do, but it is not beneficial.”


            In the 1920s and 1930s, one of the top runners of the era, Arthur Newton, wrote, “Even in the warmest English weather, a 26-mile run ought to be manageable with no more than a single drink, or at most two.”


            Until 1969 endurance athletes were discouraged from using fluids. Some sports even had rules restricting fluid use. The international governing body for distance running ruled that “refreshments shall (only) be provided by the organizers of a race after 15 km or 10 miles, and thereafter every 5 km or 3 miles. No refreshments may be carried or taken by a competitor other than that provided by the organizers.”


            In fact, it wasn’t until about 30 years ago that athletes were encouraged to drink water during workouts and competitions. When I went off to college in the 1960s, I can recall thinking what a great luxury it was to be allowed to occasionally have water during practice sessions. While in high school I was taught that athletes must adapt to thirst and dehydration. It would make us tougher, was the coach’s reasoning.


            Today we know just the opposite is true: Dehydration reduces performance. For every 2.2 pounds of water (about a quart) lost during exercise in the heat, heart rate increases by about eight beats per minute, the amount of blood pumped by the heart per beat declines by about one quart per minute, and core temperature rises about a half degree. If a 150-pound man loses two percent of his body weight, about six cups, his work output will drop off by up to 20 percent. A four-percent loss can cause a 30-percent decline in performance and put the athlete at risk for heat exhaustion.


            Dehydration may also be associated with cramps, which are more common in early season races than later in the year when adaptation to the heat is more likely.


            What can you do to prevent dehydration now that summer’s heat is beginning? Here are some tips that may help.


            • Drink frequently. Start the day by drinking water and continue by downing four to eight ounces hourly throughout the day. Keep a glass of water at your work station so you don’t have to get up to drink.


            • Go easy on diuretics. When the weather is hot or humid, cut back on coffee and alcohol which speed the removal of body fluids.


            • Drink before start. Starting about 20 minutes before a hot race or intense workout, put away 16 ounces of water or sports drink, about the size of a regular water bottle. This will fill your stomach getting fluids into the gut faster than if you wait. With only 20 minutes or less until the start, the water will not get your kidneys.


            • Guzzle—don’t sip. During a race or workout, you’ll get more water to the working muscles faster if you drink large quantities periodically rather than sipping small amounts frequently. The stomach quickly empties into the small intestine, where it is absorbed, when it is full. Drink about 20 to 24 ounces of fluid per hour during intense exercise as that’s about the most the body is capable of absorbing, on average. This varies considerably from person to person, however. Some may only be able to absorb 10 ounces, while others can take up 40 or even 50 ounces.


            • Use a sports drink. For events lasting 90 minutes or longer, a sports drink is the fluid of choice. Most studies show that a carbohydrate concentration of up to 8% empties just as fast as water. Most commercial sports drinks are 8% or less. A little sodium in the drink has also been shown to improve absorption. One gram of sodium per liter of water is about right. Cold fluids are also absorbed faster than warm fluids.


            • Carbohydrate load. If your race is an important one that lasts longer than about two hours, carbohydrate loading may help you avoid dehydration. For every gram of carbohydrate stored, two grams of water are socked away in the tissues. So if you’re able to load an additional 600 grams of carbohydrate, you’ll also pack in 1200 grams of water, or about 42 fluid ounces (126 ml). When glycogen breaks down to release energy during the race, the water is released. That’s more than a quart of water held in reserve. This will cause a two- to three-pound rise in body weight, but think of the extra water weight as an advantage—which it is.


            • If you eat—drink. If your race is long enough that you will take in food or gels, you need to drink extra water. Putting a dry foodstuff in your stomach causes the body to pull fluids out of the bloodstream into the gut where it is digested. This can cause dehydration and slow performance by making the blood thicker. Drink six to 12 ounces of water with food, depending on the amount eaten.


            • Use glycerol. Glycerol is a syrupy, sweet-tasting liquid that turns your body into a sponge that holds 50% more water than is otherwise possible. It’s available in bike and running shops, health food and specialty stores, and through catalogues. Follow the directions on the label. As with anything new, try it with a workout rather than experimenting with it in a race.


            For good performances in the heat, it’s important to avoid even a little dehydration as it slows the gastric emptying rate. You may not be able to recover throughout the race as a result. Thirst is not a good indicator. When you notice the need for water, it’s already too late—you’re dehydrating.