How to Prevent Dehydration During a Run

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Cross Training For Runners
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Written by :

David Dack

Feeling dizzy and exhausted while running? Then you might be logging the miles dehydrated.

Here’s the truth. Dehydration can impact your running performance and health like nothing else. All runners need to pay attention, regardless of age or fitness level.

Here’s the full guide to hydrations, warning signs, and why runners need to be proactive about what and how much they’re drinking.

Sounds exciting?

Let’s get started.

What is Dehydration

Dehydration happens when you lose your more fluids, usually via sweating, than the amount you take in. You’re technically dehydrated when you lose more than two percent of your body weight in fluids.

This, in turn, zaps your body out of the water and fluids needed to perform its normal functions.

And athletic performance is no exception, as losing two percent of body weight in fluids may lead to a 4 to 6 percent drop in running performance. Not cool at all.

Of course, don’t take my word for it. The American College of Sports Medicine reported that dehydration of around two percent of body weight hinders aerobic performance in mild to hot weather.

In fact, the higher the levels of dehydration, the worse the exercise performance.

Therefore, if you’re serious about running your best, make it a goal to start your run/race well hydrated, and then keep your fluid levels throughout the run and replenish them afterward. Nothing complicated.

The Causes of Dehydration in Runners

Technically speaking, dehydration while running can be blamed on various factors.

These include

  • Sweating and heavy breathing, or respiratory losses
  • Energy burning as measured from indirect calorimetry measurement, or substrate oxidation
  • Lack of water availability in the bladder
  • Water oxidation

Combined, these variables can lead to a loss in body fluids that sets the stage for dehydration, especially over time and/or when the fluids are not replaced.

Additional resource – Here’s how much water a runner should drink

Why Hydration Matters

Whenever you run or exert your body in any way, you sweat. This triggers a chain of reactions that leads to reduced running performance, especially if you fail to replace your body fluids as soon as possible.

Few things can compromise your running performance faster than dehydration as a runner. Drinking enough water is key for protecting against heat-related conditions, such as heat stroke, which can have dire consequences.

What’s more?

Dehydration can slow you down. This research has found that even a small decrease in hydration can impair athletic performance.

When you sweat, several things take place.

  • Your blood volume reduces, limiting the amount of blood returning to your heart.
  • The amount of blood your heart pumps declines
  • Your working muscles will receive less oxygen-rich blood
  • Your body will aerobically produce less energy
  • You’ll be forced to slow down.

That’s not a pretty picture, right?

Additional Resource – Why Do I sweat too much while running?

Here are the signs of dehydration.

As dehydration gets worse, the symptom will become much more severe, including:

  • Muscle cramps
  • Heavy legs
  • Intense headaches
  • Nausea and confusion
  • Gi distress
  • Extreme fatigue
  • Stopping to sweat altogether
  • Sharp decrease in running performance and output
  • Dark urine with less volume

Ignore these, and hydrastine can rapidly cause heat exhaustion or heat stroke, resulting in hypovolemic shock and eventually death.

Additional resource – How to prevent nausea when running

Stats on Dehydration

Think you’re already drinking plenty of water, think again.

Research has reported that over 75 percent of Americans are walking around dehydrated.

If you happen to be one of the dehydrated ones—and you’re a runner—logging the miles may mean putting yourself at risk.

Any sliver limning?

Research has reported that following a thorough hydration plan during exercise, when compared to drinking only when thirsty, improves endurance performance, and it will help you ward off some of the nasty symptoms below.

How to Prevent Dehydration During a Run

To prevent dehydration while running, take the following measures.

Additional Resource – What’s the best temperature for running?

Drink Water

The best way to prevent dehydration is, of course, to drink enough water all day long—and not just around your workouts. This means having frequent glasses throughout the day instead of chugging larger amounts in one go

The problem with drinking too much water within a short time is that it will force the kidneys to flush it. This, in turn, leads to frequent bathroom breaks. And you don’t want that.

What’s more?

When you chug in too much water, you’re also diluting your body’s sodium balance, increasing your risk of hyponatremia during your run. Hyponatremia is as bad as dehydration.

As a general rule, aim to drink roughly 2-3 mL per pound of body weight three hours before a workout.

If you’re running for a long time and/or exercising in the heat, consider adding a sport or energy drink to help restore carbs and electrolytes.

Timing also matters. Let me explain.

Before Runs

Start your runs well hydrated. Overall, I’d recommend drinking 16 to 20 ounces of fluids two to three hours before running and another 8 ounces 20 to 30 minutes before starting your session.

Additional reference – Stop peeing when running

During Running

You might not need to drink on the run for a session lasting less than an hour that invokes moderate effort.

Instead of pouring water over your head, drink it. Drinking cools you from the inside out.

As a rough guideline, take 4 to 6 ounces of water every 15 to 20 minutes during your long runs—or any run exceeding one hour.

Running a long distance? Consider sports drinks with 4-6 percent carbs to replace lost carbs and electrolytes.

After Running

To replace your fluid losses after a run, drink 16 to 24 ounces—roughly two to three cups—of fluid for every pound of bodyweight lost during training.

You should also keep track of your fluid intake, thirst, urine color, sweat loss, and bodyweight changes. And remember that it’s more efficient to drink tiny amounts of water throughout the day rather than a lot all at once.

Keep Track

Drinking water helps you stay well hydrated, but keeping track of your hydration levels ensures you are actually taking in enough fluid or too much.

The easiest way to keep tabs on your hydration is to check your urine. If it’s lemonade or straw color, you’re well hydrated. But if the urine is dark and yellow—think apple juice color—you need more fluids.

Another reliable way to monitor your hydrating is by measuring your sweat rate. This is especially helpful following a long run in which you’re pretty sure you have lost a lot of body fluids.

You can do this by taking your pre-run bodyweight and deducting your post-run bodyweight, recorded in an ounce. The number you get is the amount of fluid burned during training.

The test is simple. Weigh yourself before and after running. Ideally, you should weigh roughly the same.

But if you noticed that you’d lost more than a few pounds, then you’re likely not drinking enough water.

Only shed one to two percent of body weight? Then you’re likely in the hydration sweet spot. But losing more than two percent of your body weight means you need more hydration during your long runs.

Additional resource – What’s the best temperature for running

How much?

As far as I can tell, there’s no one-size-fits-all hydration rule for runners since everyone has a different body weight, sweat rate, training level, exercise effort, speed, etc.

However, most experts drink about 16 to 24 ounces of fluid for every pound lost, then plan to boost your fluid intake the next time you run.

In other words, if you shed more than two to three percent of your body weight during a workout, drink around 1.5 liters of fluid for each kilogram of lost body weight.

I’d also recommend eating something—think of a snack that contains some carbs and protein—to help kick off the recovery process.

Remember that it’s not easy to maintain your body weight during a long run, especially during the summer, so don’t feel alarmed if you lose more than a few pounds following a long run.

Additional resource – Ice bath for runners

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