Although many marathons are typically scheduled for the spring, the COVID-19 pandemic has forced race organizers to push back many events until the fall. Consequently, runners may now find themselves marathon training during the dog days of summer, which can be challenging for hydration, one of the most important parts of fueling the body in the heat.
Not only can dehydration decrease performance, but it can also be life-threatening. When training in the heat, runners should follow a hydration plan to maximize performance and stay safe.
Running in the Heat
"Training in high temperatures and humidity can greatly increase the sweat rates of runners," says Jennifer Williams, MPH, research scientist at Abbott. While running, muscle contractions and increased blood flow cause a rise in body temperature. "Hot skin, from sweltering runs in the sun, also increases peripheral vasodilation — or the expansion of our blood vessels — which can compete with our working muscles for blood flow demands, ultimately increasing cardiovascular strain during a run in the heat," adds Williams.
As a result, the body produces sweat to cool down. In fact, running in the heat and humidity can produce about 3–4 liters of sweat per hour.
Even with a rehydration plan, sweat loss during exercise can be significant, especially in hot and humid environments. "While hot temperatures can certainly affect how much a person sweats, other factors play a role as well, such as genetics, body weight, metabolic efficiency and heat acclimatization," notes Williams.
Proper rehydration and replenishment of nutrients after each training session is key to being prepared for the next one, especially if you are running most days of the week
Jennifer Williams, MPH, research scientist at Abbott
5 Hydration Tips to Consider
"There's no 'one-size-fits-all' recommendation for hydration or rehydration for running or other sports," says Williams. That said, you can follow a few tips to build a hydration plan that works for you. Here are five strategies to keep in mind.
1. Start your run hydrated. Drink plenty of fluids — including water, sparkling water and unsweetened iced tea — prior to a run. In addition, eat a variety of water-rich foods, like fruits, vegetables or broth-based soups. "Twenty percent of our daily water intake comes from foods like watermelon, strawberries, grapes, cucumbers, red peppers and chicken noodle soup," explains Williams.
2. Check your urine color to assess your hydration status. "Clear to light yellow urine is optimal. If it's darker in color, dehydration may be a risk during or post-run," says Williams. "Anywhere from 40 to 60 percent of adult athletes are hypo-hydrated (under-hydrated) at the start of an event." This can greatly affect how you feel during a run, as well as your performance and your recovery, so it's important to consider.
3. Hydrate during a run. "When first starting out on runs in the heat, consider setting up water stations throughout your route or carry a small, accessible water pack," suggests Williams. Most marathons will have hydration stations along the route, so mimicking that in your marathon training is key.
4. Rehydrate after a run. "Proper rehydration and replenishment of nutrients after each training session is key to being prepared for the next one, especially if you are running most days of the week," says Williams. Not only do you need to replace the fluid you lost in sweat, but you also need to pay attention to electrolytes. Sodium and chloride are the primary electrolytes lost in sweat fluid, in addition to smaller amounts of potassium, calcium, magnesium and phosphate.
"You can replace fluid and electrolytes by consuming water with a salty meal or an oral rehydration solution (ORS) like Pedialyte® Sport, which has three times the electrolytes and 1/4 the sugar of the leading sports drink*," notes Williams.
5. Keep a simple diary. For each run, track your run mileage, the heat index, how you felt during and afterward, and how you could improve your preparation and recovery. Doing so can help you monitor your hydration and address any hydration needs on future runs.
How to Spot Dehydration
"Dehydration happens when you lose more body fluids than you replace in your foods and beverages," says Williams. This can happen relatively quickly when you train in the heat and sweat profusely. Common symptoms of mild dehydration include headache, dizziness, confusion, thirst, bad mood, fatigue, dry mouth, constipation, dry skin and dark urine color. Accordingly, it's crucial to identify and address dehydration quickly.
"Mild dehydration can be managed by prompt and smart rehydration actions: consuming water and a salty snack like pretzels, baked chips or nuts, or an oral rehydration solution like Pedialyte® Sport," explains Williams. It's important to replace both fluid losses and electrolytes. That's why an electrolyte beverage, like Pedialyte® Sport, is recommended for managing mild to moderate dehydration.
"Along with these common symptoms of mild dehydration, you may experience negative effects during your run: increased heart rate, increased body temperature, distraction, muscle fatigue or cramping, and lower endurance or more perceived effort," notes Williams.
If you start cramping or feeling any of the other symptoms Williams describes, you should stop running, find some shade and sip on an electrolyte beverage while you rest. If symptoms persist, you're vomiting or your cramps/symptoms last more than an hour into rest, you should consult with a physician or urgent care facility. Alleviating symptoms of heat illness is key to preventing a life-threatening heat stroke event.
* Pedialyte Sport products have 1380mg sodium and no more than 14g sugar per liter; leading sports drinks have ≈460mg sodium and ≈58g sugar per liter.
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