The body is composed of 50-70% water (norm = 60%), and maintaining this balance is critical in regulating body temperature and cellular stasis. For endurance sports athletes, proper hydration is a key factor in effective training and race performance. A common problem with endurance athletes is hypo- or dehydration, which occurs when fluid loss is greater than intake before, during, or after bouts of exercise. When, how much, and what you combine with your water, can have a big impact on your training and race results, as well as recovery.
Whether you're training or racing, maintaining proper hydration balance before, during, and after exercise will ensure you're giving your body an ideal platform to work from. A reduction of total body water as small as 2% can significantly hinder your aerobic performance. One important role water plays during exercise is regulating body temperature. When a state of hypo-hydration exists, your body's cooling efficiency is compromised. And this 'over-heating' leads to a reduction in your athletic performance. The Institute of Medicine recommends the following guidelines for sedentary people: men aged 19-70 y/o require 3.7L/day, while women 19-70 y/o is 2.7L/day. Hydration sources include water, other liquids, and foods. Endurance athletes however, require much greater amounts of fluids to keep their bodies properly hydrated, and must add to the above values.
To effectively plan hydration needs, athletes must also consider how long they train each day, as well as the type of climate they train in. As a general rule, for every pound of body weight lost between the start and finish of an exercise session, replace your water loss by consuming 20 ounces of fluid, or 600ml of fluid/per 0.5kg of lost body weight . One way to monitor your fluid needs would be to take your weight immediately before and after your exercise bouts, and measure the change in body mass from water loss (sweating). For those without access to lab tests, body mass change is the most effective way to self-monitor your hydration needs.
Other self assessment methods include urine color and rating of thirst. Urine color should be no darker than the color of straw, while thirst rating can be more subjective. As a general rule, keep your fluid intake consistent enough that you never feel thirsty. Taking your wake-up weight can also help you keep track of your hydration balance on a 24 hour basis by making sure your daily weight does not fluctuate. Combining wake-up weigh-ins with a body mass check right before and after training will help you accurately monitor and maintain a state of water equilibrium.
How long do you train? The length of your sessions also impacts what you should drink before, during, and after training. Training sessions lasting longer than 30-40 minutes require an intake of about four-to-six ounces of fluid every 15-20 minutes. For training sessions that exceed 60-75 minutes, sports drinks, with both carbohydrates (5-8%) and sodium, are recommended. Sweating rates for endurance athletes range from 1.2 to 1.7 liters per hour, but can be as high as 4.0 liters per hour.
For those who participate in prolonged periods of exercise (prolonged rows, marathons, or Ironman/cycling events) including electrolytes in water is critical to avoiding hyponatremia (low blood sodium levels). The typical sodium to potassium loss during exercise is 7 to 1, respectively. An athlete who loses 5L of fluid with daily training will need to replace 4,600 – 5,750mg of sodium, in addition to a seventh that amount of potassium.
Fluid replacement after training must focus on restoring the weight lost from dehydration (cooling), and intake should be approximately 150% of the weight lost, or 600ml of fluid per 0.5kg of lost body weight. Post-exercise meals should also contain sodium either in food or beverages, because diuresis (fluid loss) occurs when only plain water is ingested. Most commercial carbohydrate-sodium drinks contain anywhere from 50-110mg of sodium per eight fluid ounces. Sodium assists with the rehydration process by maintaining plasma osmolality (balance) and the urge to drink.
If water becomes a boring option, try eating water-loaded foods such as water melon, cantaloupe, apples, oranges and other fruits, as well as most green vegetables. Besides keeping you hydrated, these fruits and vegetables are loaded with essential nutrients. Herbal teas and even sports drinks are another way to keep your hydration and electrolyte intake in balance. Also, remember that hydration is a 24-hour process. So spread out your fluid consumption throughout the day for better absorption into cellular tissue. The body can only process so much fluid at once, so excess will be quickly voided out of the body as urine, and will not be available for the body to use.
General hydration guidelines are as follows: 16-20 ounces of water 1-2 hours before exercise, 10 to 16 ounces 15 minutes before exercise, and about 4-6 ounces of fluid every 10-15 minutes during exercise. Fluid intake should be regulated 24 hours prior to training, so if you train daily you're on the clock all the time. Hydration losses greater than two percent of your body weight could take up to 24 hours to restore. Research also shows that the volume of fluid intake generally increases when the water or fluid is flavored.
Bottom-line, train hard, drink-up and keep your cooling system in balance.
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