MAYO CLINIC -- Hot summer months can take a toll on your body, making it especially important to stay hydrated as you take on those long training runs and races. Rose Prissel, a registered and licensed dietitian at Mayo Clinic for 25 years, details the effects of hydration on running performance and shares some good strategies for staying hydrated.
Rose has a passion for sports nutrition, has supported various athletic youth groups and is currently working toward her board certification as a sports dietician. She participates in many sports, including running, biking, hiking, cross-country skiing, snowshoeing and kayaking.
Q: How does dehydration affect running performance?
A: Dehydration slows your pace and can make you perceive greater exertion during your run because it increases physiological strain. Studies show that dehydration at levels greater than two percent of your body weight degrades aerobic exercise and cognitive/mental performance, particularly in temperate to hot environments. The magnitude of performance decline is related to the severity of dehydration, and the severity of dehydration depends on several factors: your pace, the temperature, humidity, elevation and your personal tolerance for dehydration.
Q: How much fluid is recommended before a long training run or marathon? How early should I be drinking it?
A: Your goal should be to start running only after you are already hydrated. This can be accomplished by making a habit of drinking adequate fluids throughout the day and with meals. That being said, the amount of fluid you should drink depends on how soon you'll be running, what your stomach can tolerate, and your current level of hydration. If you have been able to eat and drink sufficiently with meals in the 8-12 hours prior to a long run, then you should already be close to being hydrated. Pay attention to the color of your morning urine; it should be the shade of lemonade or lighter. If, however, you have suffered substantial fluid deficits and have not had adequate time to establish hydration, then you may need to get more aggressive with your intake. You will need to start drinking fluids at least four hours before exercise to enable fluid absorption and allow excretion of any excess fluid as urine. Slowly drink 2-3 mL per pound of body weight. If you aren't producing urine or it's dark/ concentrated, you should drink 1-2 mL additional per pound about two hours before the event.
Q: How can I stay properly hydrated for a marathon without worrying about having to make frequent stops during the race?
A: If you make hydration a habit, then you should be able to complete your race with the same amount of stops you typically need during training. Your amount and rate of fluid replacement during your race depends on your individual sweat rate and the duration of exercise. It is recommended that individuals calculate their personal sweat rate so they know how to properly rehydrate; a simple online search will provide instructions to help you with this task. In general though, a good starting point for marathon runners is to drink from 0.4 to 0.8L/hour with higher rates for faster, heavier individuals competing in warm environments and a lower rate for slower, lighter individuals competing in cooler environments.
Q: What fluids are the best sources of hydration? How do fluids such as sports drinks, juice, milk, tea and coffee stack up against water?
A: Water, sports drinks, juice, milk, tea and coffee all hydrate. The benefits of each differ based on the amounts you are drinking and/or when you are drinking them. Take tea and coffee for example: caffeine in small amounts (less than 180 mg/day) does not increase daily urine output or cause dehydration, and several studies show that moderate caffeine may boost endurance. Additionally, milk, fruit juice and sports drinks can all be consumed up to an hour prior to your run. Fruit juice and sports drinks provide carbohydrates and milk has both carbohydrates and protein. During your run, sports drinks are a good source of energy and the sodium may help stimulate thirst and replace electrolytes lost through sweat. After your run, when you are in recovery mode, veggie juice, chocolate milk, smoothies and fruit juice are all good choices. Veggie juice is high in sodium which will help replace lost electrolytes and stimulate thirst. Chocolate milk and smoothies that are made from fruit and yogurt are good sources of carbohydrates to replenish glycogen and protein to stimulate muscle repair. On the other hand, alcohol can act as a diuretic and increases urine output, so it will not help hydrate you.
Q: Does it make a difference if my drink is warm or cold?
A: Some studies have suggested that drinking cold fluids may enhance performance by reducing your perceived exertion, thus allowing you to run longer. Regardless of your strategy and preferences, however, what's most important is to make sure you are hydrating regularly to keep your body running smoothly, especially in these hot summer months!
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