Fluid Dynamics

Hydration is a vital part of our everyday lives, but it’s especially important when marathon training in the hot summer months.

"Dehydration can happen relatively fast when you're training in the heat," says Jennifer Williams, MPH, a research scientist at Abbott who specializes in hydration.

After all, when the amount of fluids you lose via sweat (and other biological functions) exceeds how much you consume during training, dehydration becomes an issue. It can slow your pace, tire you out faster and put you at risk of heat exhaustion and stroke.

And water isn't the only thing your body loses as you sweat. It also secretes electrolytes like sodium, chloride and potassium, which help your body's muscle and nerve cells properly fire and function, along with some other minerals like calcium, magnesium and phosphate that are important for muscle support as well.

So even if you're a seasoned marathoner with a lot of springtime races under your running belt, you'll likely need to adjust your hydration plan and pacing during the summer.

But don't sweat it. Williams is here to share how to tackle hydration during an extra-hot training season.

1. Let Your Body Acclimate

Giving your body time to get used to hot weather will help reduce your likelihood of getting dehydrated or experiencing heat exhaustion during future training runs.

Try to limit your indoor air-conditioned runs and spend more time outside. This will help your body adapt to the climate. To stay safe during the transition, keep track of your heart rate, listen to your body and gradually ramp up mileage and pace when you're running.

Also, prioritize electrolytes and fluids before and after your workouts. Apart from helping you stay hydrated, it will help your body adapt faster to hot temps, Williams says.

2. Take Advantage of Summer Produce

About 20% of your daily water intake comes from the foods you eat, Williams says¹. And some of the most hydrating foods include summer produce, such as strawberries, watermelon, grapes, mango, papaya, and pineapple. (Bonus: they all have immune-supporting antioxidants.)

3. Go in Extra Hydrated

Anywhere from 40% to 60% of athletes start their events already dehydrated, according to Williams.^2,3,4

Don't be a statistic. "Check your urine color. If it's clear to light yellow, you're good to go," Williams says. If not, you need to drink more water before starting your workout.

4. Cool Off

Research shows that endurance athletes can go harder, longer by dropping their body's core temperature before or even during exercise.⁵ It makes sense: The cooler your core body temperature when you start a run, the more your temp will have to rise before you start to overheat.

One simple way to cool your body while hydrating, is to reach for cold beverages. Try making your pre-workout drink a cold one or putting ice in your water bottle or hydration bladder.

5. Bring Along Extra Fluids

With increased sweat rates, you likely need to drink more during your marathon training runs than you usually do. Expect to start sipping earlier and more frequently. Also, even if you can usually get through short or middle-distance runs with only water during and after them, you may need more than that now.

Depending on the situation, water may not be enough because it is low in electrolytes. You get electrolytes from what you eat and drink, and you lose them any time you lose fluids. Electrolyte specific formulas, like Pedialyte, can help you rehydrate and feel better fast.

To accommodate your increased fluid and electrolyte needs, consider wearing a (larger) hydration pack.

6. Track All Things Heat and Hydration

Use your training app or diary to outline not just your runs, but also the heat index, how much (and what) you drank and how you felt during and after your run, Williams says. You can use that information to pinpoint the hydration strategy that's best for you.

The heat index is a combination of the air temperature and humidity. It's the "feels like" temperature listed in your weather app.

7. Weigh Yourself

Mild dehydration, consisting of losing at least 2% of your body weight in water, can negatively affect your run performance and result in symptoms of dehydration.

So, if you weigh 160 pounds, your goal is to drink enough that you weigh no less than 156.8 pounds at the end of your run. (Every pound you lose during your workouts signals 16 ounces of water gone, Williams explains.)

For the most accurate measurements, weigh yourself naked before and after your training runs. After runs, your clothes will be weighed down with sweat.
‍

8. Go the "Extra Mile"

You don't stop losing sweat the second you cross the finish line. So, to fully replace any sweat losses, you need to drink more than you think within 90 minutes of your workout.

"It's recommended to drink 1.25 to 1.5 times the fluid volume that you lost," Williams said, adding, "For every pound (16 ounces) you lose in body weight, you should drink 20 to 24 fluid ounces of fluid."

1. Baker LB and Jeukendrup AE. Optimal composition of fluid-replacement beverages. Compr Physiol2014;4:575-620.

2. Chapelle L. Pre-exercise hypohydration prevalence in soccer players: A quantitative systematic review. Eur J Sport Sci 2020;20:744-755.

3.Arnaoutis G et al. Fluid balance during training in elite young athletes of different sports. J Strength Cond Res 2015;29:3447-3452.

4. McDermott BP et al. National Athletic Trainer's Association Position Statement: Fluid replacement for the physically active. J Athl Train 2017;52:877-895.

5. Sawka MN et al. Exercise and fluid replacement. American College of Sports Medicine Position Stand. Med Sci Sports Exerc 2007;377-390.