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Hydration is one of the most important elements that an individual needs to consider during endurance training. Dehydration occurs when a person doesn’t drink sufficient fluids and it WILL impair your endurance performance, while also reducing physical and mental function and increasing risk of heat cramps, heat exhaustion or heat stroke. Sweat loss varies by individual and is also dependent on weather conditions and exercise intensity. In order to avoid water deficiency and its adverse effects, you need to stay hydrated and unfortunately, when you feel the sensation of thirst, it is too late, dehydration has already begun.
During endurance training, you should have enough fluid to prevent thirst from setting in. To prevent from waiting for your thirst queue, you can start a hydration schedule during your training session. The general recommended hydration schedule is as follows:
4 hours prior to exercise: drink 16 - 20 ounces of fluid
If urine is still dark, 2 hours prior: drink an additional 12 – 16 ounces
10 – 20 minutes before exercise: drink 7 – 10 ounces
During exercise: EVERY 10 - 20 minutes drink additional 7 -10 ounces
These are general guidelines that will help maintain your hydration status during training; however, sweat trials should be performed to be able to individualize your plan. Here is one calculation you can use:
Calculation of sweat loss: Body weight before exercise (lb) *without shoes + fluid intake during run (convert from oz to lb, 16 oz = 1 lb) – body weight post-exercise (lb) *without shoes = total sweat loss not replaced.
What if I Don't Sufficiently Replace my fluids?
The sweat that is lost during training contains electrolytes that are necessary and important for optimal body function. During prolonged exercise (long mileage days), you may not always be able to equally replace your fluid loss. In those instances, it will be of upmost importance to focus on replacing the electrolytes through commercially available sports drink and other supplements which will rehydrate your body, replace your necessary electrolytes, and also can provide carbohydrates. To find out more about importance of carbohydrates, check out my article titled "What is Glycogen and Why Do We Care?" However, at what mileage this occurs is going to strongly depend on each individual’s sweat rate.
What Constitutes as a Good Pre-Workout Fluid?
There are many options that you can choose from to meet your pre-run fluid needs. Of course, water is always a great option; however, you can combine the total volume needed with water, juice, and milk. 100% juice will provide your body with fluid, carbohydrates, and electrolytes. Milk also provides fluid, carbohydrate and protein. For most individuals, using these additional fuel sources 2 to 4 hours prior to exercise shouldn’t cause any gastrointestinal discomfort. However, immediately using prior to exercise may cause discomfort and for those that have sensitive GI tracts may find some discomfort in drinking thicker, higher concentrated fluids prior to exercise. You definitely want to test out your GI tract on some lower mileage runs to find out what works for you before you get too deep into your training. Always test out your fuel sources because your body is slightly different than every other person that is training with you. What works for your friend may not work for you!!!
What Can I Drink During My Exercise to Keep Me Hydrated?
Your choice of fluid during exercise will depend on the duration and demands imposed on your body. On longer activities, your body will begin to demand more than water. It will need water, carbohydrate and electrolytes. For longer runs in colder weather you may need to add a more concentrated carbohydrate drink that will supply energy to your working muscle. However, as the temperature begins to increase, your sweat loss will also increase. You will then want to start considering the addition of a carbohydrate-rich electrolyte drink. You may want to strongly consider training with the sports drink that will be offered on race day at the hydration stops. You will not be able to carry a sufficient amount of sport drink needed to keep you hydrated. For those of you that don’t want to rely on what the race program is going to offer you should start testing out alternate options such as sports gel, sports beans, or sports shots.