By Arnie Baker, MD
Hydration Key Points
- Adequate hydration is crucial to athletic performance.
- Keep fluids handy.
- Begin training or events hydrated.
- The longer the event, the more important it is to keep up with fluid losses.
- For single-day events:
- Aim to drink 16 ounces (2 cups, 500 milliliters, 1 standard waterbottle) per hour while exercising moderately or in temperate conditions.
- Aim to drink up to 32 ounces (1 quart, 1 liter) per hour when exercising at high intensity or in the heat. •
- For multiple-day events:
- Replace fluids lost, up to 48 ounces (1.5 quarts, 1.5 liters) per hour when exercising in the heat.
- Reduce exercise intensity to a level that allows you to replace what you are losing.
- Chilled and flavored fluids improve palatability and promote hydration.
- Carbohydrate concentration to a maximum of 6% (240 calories per quart or liter) may improve the rate of rehydration as well as improve performance by providing energy and sparing glycogen.
- Sodium to a maximum concentration of 1,000 milligrams per quart (liter) may improve the rate of rehydration as well as prevent hyponatremia.
- There is no evidence that other minerals in hydration products improve performance.
- There is no evidence that proprietary substances in sports drinks confer any advantages over readily available nutrients.
Requirements: Adequate Intake (AI)
The 2004 US Food and Nutrition Board (FNB) adult daily total water intake AI is 3.7 liters (quarts) for men and 2.7 liters for women.
This includes all water contained in food, beverages, and drinking water.
Aerobic endurance athletes need more.
Dehydration worsens athletic performance.
Replacing liquids that are lost through exercise is one of the easiest and important aids to performance in endurance sports.
Fluids are intracellular—within cells, and extracellular—for example in blood vessels.
Fluids allow the body’s cells to function optimally. Maintaining good hydration is essential to maintaining strength while exercising.
Blood is about 50% fluids. Reduction of blood volume from dehydration affects performance quickly.
Dehydration may reduce not only current performance but also subsequent training effectiveness. It is associated with a decrease in metabolic rate and a shift to carbohydrate energy use at rest—resulting in less carbohydrate available for high-intensity exercise.
A conscious effort to drink may be required—most athletes do not voluntarily drink enough.
It is easy to get dehydrated. Over-hydration is unusual, but occurs—most often in those who exercise at low or moderate intensity for many hours and overdrink, especially with salt-poor solutions.
What Percent Dehydration Affects Bicycling Performance?
Some studies have shown that as little 2% dehydration (3-pound weight loss for a 150-pound athlete) affects performance.
These studies are often touted by coaches, sport scientists, and companies that market hydration products.
It is not that simple; and not all studies come to this conclusion.
For example, four other studies showed that:
- More than 20% of both boys and girls lost more than 2% of body weight during a triathlon consisting of an 800-meter swim, 30-kilometer bike, and 8-kilometer run. Performance was better in the more dehydrated athletes.
- Neither 2% nor 4% dehydration adversely affected performance.
- A 3.5% reduction in body weight from dehydration was not associated with decreased muscular strength or endurance compared with a 1.3% reduction in body weight.
- One-hour cycle time-trial performance was not improved by hydration during the event.
In the real world, modest dehydration probably does not affect performance, and for events less than one hour, hydration has not been proven as important as it is for longer events.
Although laboratory performance has been shown to worsen with modest dehydration, in real world competition many 10-K runners and 40-K bicycling time trialists do not drink, even in desert events. During races of less than one hour at maximum effort the disruption of rhythm, the time cost of drinking and the aerodynamic drag of water bottles, may justify not drinking.
The longer the event, the more important it is to pay attention to hydration. Prehydrate and pay attention from the get go—because once behind, it is often difficult to catch up.
Your body responds to dehydration with a sense of thirst. If you are thirsty, dehydration has already happened. The older we get, the slower our body’s thirst response becomes.
Athletes are often unaware of and underestimate their fluid losses and replacement.
In one study, experienced runners lost almost 2-quarts (liters) in a 10-mile run. They estimated their sweat loss to be 1.1 quarts (liters).
In Hawaii Ironman subjects, dehydration was 20 times more common than overhydration.
Estimating Sweat Rate
Athletes can roughly estimate sweat rate by weighing themselves before and after exercise and accounting for urine losses and fluid ingestion.
One quart (liter) of water weighs about 2 pounds.
However, a scale can be misleading.
Glycogen binds, on average, three times its weight in water. Since glycogen depletion is common in events longer than one hour, some weight loss reflects decreased glycogen stores rather than hydration status per se. Glycogen stores normally average about 1 pound (500 grams). If glycogen is completely exhausted, 4 pounds (2 kilograms) of weight loss can be attributed to glycogen exhaustion—1 pound of glycogen and 3 pounds of associated bound water.
If you are training or racing in hot weather, or repeatedly exercising within a short span of time, particular attention must be given to adequate prehydration in the days before racing.
Athletes traveling to races commonly drink less because they neglect to fill or bring waterbottles and are trapped in car or airplane seats.
You want not only your blood vessels to be hydrated, but your cells to be filled as well. Consciously drink plenty of fluids and look for clear urine for several days before racing.
Look for Clear Urine
You generally know that your blood is well-hydrated when your urine is clear. Two caveats: B vitamins may color the urine, and, conversely, clear urine does not guarantee that you are well-hydrated.
Urine color was found to be reliably correlated with percent dehydration during a 30-mile mountain bike race that followed a pre-exercise hyperhydration protocol.
Does concentrated urine mean that one is not well-hydrated? That is the common view. In fact, NCAA wrestlers cannot have their body composition measured for the wrestling season if specific gravity is >1.020. However, a study following well-hydrated volunteers found urine specific gravity was often more concentrated than that level.
Lost blood fluid volume is quickly replaced by drinking water. Cell dehydration, however, is different.
The cells of your body are mostly water. Fluid loss from the cells may take many hours, or even a day or two, to replace. It is possible to experience cell dehydration, drink a lot, have clear urine, and still be dehydrated in the cells.
When you drink, the fluids travel from your gastrointestinal tract into your bloodstream. The kidneys immediately sense the fullness
of the blood vessels and begin to eliminate what they perceive as surplus fluid. However, your cells may not have had time to absorb fluids and so remain dehydrated.
It is a little like a plant that has not been watered for some time. The soil is dry, and the roots and leaves are dehydrated, so you water it. Before the plant can absorb the water, it has run through the porous, dry soil, leaving the plant leaves still dry.
Keep Fluids Handy
Having fluids readily available encourages drinking.
Hydration backpack systems make sense in some sports. Hydration systems can carry 100 ounces (3 quarts or liters), the equivalent of six standard waterbottles. They can be accessed more easily than waterbottles for some athletes, for example some mountain bikers or unskilled road riders.
Hydration backpack systems were associated with slightly better hydration and performance than traditional frame-mounted bottles—in a mountain-bike study funded by CamelBak, a backpack hydration system.
Chilled and flavored fluids improve palatability and promote hydration.
Studies have shown that both sodium and carbohydrate improve the rate of absorption of fluids from the gastrointestinal tract and reduce fluid losses in the urine.
Solutions with higher than 6% carbohydrate concentration may delay stomach emptying, slow hydration, and cause gastrointestinal cramping. The hotter or more fatigued the athlete, the less the athlete is able to tolerate concentrated fluids.
Most commercial sports drinks contain too little sodium (salt). Higher concentrations of sodium (40+ milliequivalents per liter; or 1,000 milligrams per quart, liter) are more effective for rehydration.
A solution containing sodium 75 milliequivalents per liter (1,875 milligrams per liter or quart) enhances fluid retention more than a solution containing 20 milliequivalents per liter (500 milligrams per liter or quart).
The mouth and the gut are different. Although the gut absorbs sodium-rich fluids better, many athletes cannot get them past the mouth because the mix tastes revolting. Salty snacks may be a better way to replace your sodium.
How Much Water Can You Lose?
Sweat rates have been reported higher than 3.5 quarts (liters) per hour with heavy exertion in the heat.
More typically, athletes sweat about 16 ounces (½ quart, 500 milliliters, 1 standard water bottle) per hour when exercising moderately in cool or temperate conditions.
Athletes sweat about 32 ounces (1 quart, 1 liter, 2 standard waterbottles) per hour when exercising moderately in hot conditions.
I sometimes ride from Del Mar to San Clemente, California, and back—about 85 miles. On the way, I drink from my two large water bottles. In San Clemente, I buy two or three bottles of fluid. I drink one there and use the rest to refill my water bottles. On the average, I leave at 147 pounds and come back at about 142 pounds. If I am 5 pounds lighter at the end of the ride, it means I am still down more than 2 quarts of fluid.
Once I rode a 40-K time trial in 90°+ heat and high humidity. I drank 2 gallons within an hour of the end of the ride—and I still was not tanked up.
Once I went on a desert trip with my wife and rode a century. Both of us needed to replace almost one-third of our weight in fluids that day. I drank 45 pounds—almost 5 gallons. That is 20 quarts. That is eighty 8-ounce glasses of fluid!
It is easy for the body to use a lot of fluid quickly.
How Much Should You Drink?
It is generally recommended that athletes consume enough fluids to replace sweat and urine losses during training and events.
Few athletes do.
Since not all that is drunk is retained (about 60% is eliminated by the kidneys as urine), some advocate rehydrating with 150% of lost fluids. Studies show that 50% to 100% more fluid is required, depending upon simultaneous sodium ingestion.
Aim to drink 16 ounces (500 milliliters, 1 standard waterbottle) per hour while exercising moderately or in temperate conditions.
Aim to drink up to 32 ounces (1 quart, 1 liter, 2 standard waterbottles) per hour when exercising at high intensity or in the heat.
Most athletes cannot drink more than 32 ounces per hour and so get dehydrated during training or events in the heat. For many events, modest dehydration is not a problem.
Ultraendurance and Multiple-Day Training/Events
For ultraendurance events that last more than a single day, or athletes repeatedly competing over several days, athletes cannot afford to get behind. They must keep up with fluid losses.
Athletes can learn to tolerate up to 48 ounces per hour.
Replace fluids lost, up to 48 ounces (1.5 quarts, 1.5 liters, 3 standard waterbottles) per hour when exercising in the heat.
If you cannot keep up with losses, pace: Reduce exercise intensity to a level that allows you to replace what you are losing.
Weight loss during exercise is directly related to fluid losses during exercise.
Predicting fluid loss before exercising based on initial body weight, exercise type, exercise intensity, ambient temperature, and percent relative humidity accounted for only about half of the variability of observed loss in recreational exercisers.
Cycling in a hot environment for an hour? Drinking 1,000 milliliters of cool water immediately before cycling or splitting the fluids into four 250 milliliter doses at 0, 15, 30, and 45 minutes during the hour results in no significant thermoregulatory or performance differences.
What is lost with sweating and hard breathing (the lungs moisturize air) is mostly plain water. Some electrolytes or salts (sodium, potassium, chloride, etc.) are lost, but it is mostly water. Water is the most important item to replace.
Expensive athletic drinks or solutions are not necessary for usual athletic activity.
Electrolytes may help the body absorb and retain water. Aerobic endurance athletes who exercise daily for more than a couple of hours can deplete the body’s reserves of some electrolytes, principally sodium and chloride.
Sodium and chloride may come from salty snacks, supplements, or be present in fluids consumed.
CAUTION: Rehydrating without adequate sodium can result in low blood sodium or hyponatremia, potentially life-threatening.
Calories in solution help water and electrolytes move from the gut into the bloodstream.
For exercise more than 1 hour in duration, studies have shown that solutions containing carbohydrate allow for improved performance compared with plain water.
A few studies have shown that calories can help performance even during shorter events.
Sports drinks, soft drinks, and fruit juices provide the calories as well as replace some of the modest electrolyte losses that occur with sweating. Note that fruit juices must usually be diluted to be tolerated while exercising, and that even so, some individuals do not tolerate fruit sugar (fructose) as well as other sugars.
Even if you are only going to exercise a short time, it makes sense to always have some calories in what you drink. They may not be necessary for performance today, but who knows—maybe you will end up exercising longer than you were planning, or perhaps it will help you keep your glycogen topped up and allow you to perform better tomorrow. Those who train daily or exercise more than 10 hours per week are always fighting glycogen depletion.
Sports drinks can be helpful. Before- and during-exercise sports drinks generally do not contain protein or fat. These ingredients are sometimes included in recovery drinks.
Some riders cannot tolerate the fruit sugar (fructose) in fruit juices, whereas other simple carbohydrates, including glucose, may not present a problem.
As described earlier, because the intestines often react to the number of sugar particles in solution, stringing together single-molecule sugars into chains of glucose polymers or maltodextrins may allow more calories to be consumed without increasing gastrointestinal upset.
There is hardly any evidence, though much hype and promotion, that adding a small amount of protein to drinks may improve recovery.
Make Your Own Sports Drink
For a standard 16-ounce waterbottle, mix:
- 16 ounces water
- ½ cup maltodextrin
- 1 to 2 tablespoons of concentrated lemonade or fruit juice
- 1/16 teaspoon salt
Each 16-ounce bottle will contain about 200 calories and 100 mg of sodium. This may not provide enough sodium when many waterbottles are required during the course of training or an event; even so, this may taste too salty for some athletes. If so, rely on salty snacks for your sodium.
Proprietary sports drink ingredients have not been show to offer any advantage over standard ingredients when independently studied.
The manufacturer of Revenge claims it may improve performance by decreasing blood viscosity. Not so in a study that examined ingestion of 20 ounces of the product.
Although one study showed that oxygenated water benefited highly-trained cyclists, almost all studies show no benefit.
Whether there can possibly be any help from this product is doubtful. Look at it this way:
- One quart (liter) of tap water contains about eight milligrams of dissolved oxygen.
- One company claims its product contains four times that—32 milligrams.
- A 154-pound (70 kilogram) recreational athlete with a VO2 max of 50 milliliters/kilogram/minute will use about 100 milligrams of oxygen every second.
- To get a one percent boost, athletes must chug 2.5 quarts (liters) of oxygenated water every minute for each minute of exercise.
- The technical term for this is drowning.
Glycerol, a three-carbon molecule, forms the backbone of triglycerides. It may also act to increase hydration, but so does a little extra salt in the diet.
Studies examining the effectiveness of glycerol have had mixed results, mostly negative. Cramping and weight gain are side effects.
Adding common salt to the diet 24 to 48 hours before prolonged exercise in the heat may be as, if not more, valuable.
We were back at my car after a 60-mile ride. I had a gallon thermos of drink in the trunk. A previous Olympian was with me. He was thirsty. I gave him some purplish fluid.
“What’s that?” he said, swallowing eagerly. “That’s great. Is it Cytomax, or a new energy drink?”
“Not too strong?” I asked.
“No. Terrific. Is this why you go so fast?
“Don’t know, but it helps,” I said.
“What is it? Who makes it?” he asked again.
“It’s from the grocery store,” I said. “Tropical Fruit, made by Dole. 100% pure juice, diluted about 50/50 with water.”
“Wow!” he said. “Real juice!”
To get you going or keep you going, caffeine in solution (for example, coffee, tea, Coke, or Pepsi) can be useful.
For a discussion about the ergogenic (performance-enhancing) and ergolytic (performance-robbing) effects of caffeine, see pages 114 and 125.
Alcohol is ergolytic—performance-robbing.
Like caffeine, it is a diuretic robbing you of fluid. It slows you down. It makes your legs heavier. Physical activity increases the intoxicating effect of alcohol. With your judgment impaired, skills worsen. On a bicycle, you can easily crash.
Make It Taste Good
Plain warm water does not taste great. Chilled fluids go down more easily. A little flavor, a little sugar, a little electrolyte makes it taste better. Do not overdo it: too sweet or too salty tastes bad. Having good-tasting fluids allows you to drink more.
Palatability changes depending upon hydration status and exertion level. (What tastes good at rest does not taste the same when tired, hot, sweaty, and exercising.)
Review the key points at the beginning.
Hydration improves performance. Although some level of dehydration may be tolerated without adversely affecting performance, the longer the event the more important it is to pay attention to hydration and have a hydration strategy.
Carbohydrate, sodium, flavor, cooling of fluids, and accessibility can help improve hydration.