Trail Running Hydration: The Quick and Dirty

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Welcome to this month’s edition of “Where the Road Ends: A Guide to Trail Running,” where we discuss the basics of trail running hydration. “Where the Road Ends” is the name of both this column and the book Meghan Hicks and Bryon Powell of iRunFar published in 2016. The book Where the Road Ends: A Guide to Trail Running is a how-to guide for trail running. We worked with publisher Human Kinetics to develop a book offering the information anyone needs to get started, stay safe, and feel inspired with their trail running. The book Where the Road Ends teaches you how to negotiate technical trails, read a map, build your own training plan, understand the basics of what to drink and eat when you run, and so much more.

This column aims to do the same by publishing sections from the book as well as encouraging conversation in the comments section of each article. We want you to feel inspired and confident as you start trail running as well as connected to iRunFar’s community of off-road runners!

In this article, we excerpt from Chapter 6 to talk about the basics of trail running hydration.

Why is Trail Running Hydration Important?

Almost every part of your body needs water to operate, and water makes up well over half of your body’s weight. Your blood needs sufficient water to transmit oxygen and nutrients around the body. Your muscles need it to perform their continued contractions. Your kidneys require water to excrete waste products from your body. And on it goes.

When you run, you lose water through sweat, respiration, and waste elimination. You should replace whatever water you lose. But you don’t always need to do that during your trail run, so much as over the course of a day. In this way, we like to think of trail running hydration as all the hydration you do–on and off the trail.

Trail Running Hydration and Drinking to Thirst

Magda Boulet is an Olympic marathoner who converted to competitive trail running in 2013. She works in research at Gu Energy and has a master’s in exercise physiology. Magda also says that you need to maintain proper hydration on a daily basis, not just when you’re running. All-day hydration is where it’s at, says Boulet: “A key aspect of maximizing performance is arriving at the start of a workout or race well hydrated. Many, if not most, athletes cannot consume enough fluid during exercise to match rates of loss, which has been documented by many studies. Therefore, prehydration before starting exercise can help ensure that athletes start the event or exercise bout in a hydrated state and can improve performance.”

How can you do this? Drink when you’re thirsty, and stop when you aren’t anymore—in life, when running, anytime. It’s that simple.

The human body has thirst cues, such as the feelings of parched lips, a dry mouth, or a raspy throat. These are responses to water loss. Scientists believe that people who listen to their thirst cues by drinking when they feel thirsty and stopping when those feelings disappear, during daily life and exercise, hydrate adequately.

As recently as a decade ago, doctors were categorically recommending that we drink eight 8-ounce (240 ml) glasses of water per day, whatever our body size, our daily exertion, or the weather. Dr. Timothy Noakes, author of Waterlogged: The Serious Problem of Overhydration in Endurance Sports, points to another culturally pervasive issue, at least in our running culture–the historical recommendation to drink to excess during sports be it through water or sports drinks. But overhydration can be a serious medical issue. In response, Noakes began promoting the drink-to-thirst principle as a way to encourage people to drink the proper amount of water in daily life and during exercise.

Stephanie Howe using a running vest to carry water during the 2014 Western States 100. Photo: iRunFar

When drinking to thirst, some runners find that they feel better when they sip small amounts frequently, whereas others like to guzzle at irregular intervals. The water you drink goes to your gastrointestinal tract, and it’s then transferred elsewhere in your body. The stomach has an average maximum processing capacity of about one liter of water per hour during aerobic exercise, an amount that will vary depending on how hard you’re running, the climate in which you’re exercising, and how much liquid and material containing calories is in your stomach. If you exceed that emptying ability, water will begin to pool in your stomach, which can lead to the sensations of bloating, sloshing, and even nausea. With practice, you will learn your body’s preferred rate of water consumption.

Test the drink-to-thirst concept to learn how it works for you. Spend a day following your thirst cues, including before, during, and after your trail run. Monitor the color of your urine throughout the day. If your urine is light yellow, you’re likely adequately hydrated. Any lighter- or any darker-colored urine could mean that you’re overhydrated or dehydrated, respectively. You may find that it takes a little while to identify your thirst cues because people in Western cultures often drink for purposes other than quenching thirst.

Staying Hydrated on the Run

Most of your trail runs won’t require hydration during the run. They will be short enough that you can rely on your body’s own water-storage capability. But there will come a time in your growing relationship with trail running that you’ll run long and far enough that you’ll want to drink water while you’re running. When this happens, there are two immediate questions, “How much water should I drink and how do I carry it?”

Have a look back at this article where we talked about ways to carry water via a handheld water bottle, waist belt, or running vest. In terms of how much to drink, we return to Noakes’s adage: drink to thirst! Of course, we have to predict how much we’ll need so that we pack enough. We learned earlier in this article that the stomach can absorb on average a liter of water per hour, so use that as a general reference in packing your water supply. Once out there, stick to the plan of drinking to thirst. With trail running hydration, you are an experiment of one. Over time, how much water you pack for a run and when you drink will become as intuitive as the running motion itself.

One last thought, if you’re headed to a remote place or if it’s a hot day, carry at least some water, even if you don’t think you’ll need it. If the run takes you longer than you think or you take a wrong turn, you’ll be glad you have it!

Excerpted from Where the Road Ends: A Guide to Trail Running, by Meghan Hicks and Bryon Powell. Human Kinetics © 2016. 

Call for Comments

  • For those of you reading who have experience in trail running, can you share something you wish you new about hydration when you started?
  • Do you have questions about the basics of trail running hydration? Leave a comment and we’ll do our best to answer them!

Samir Akhdar has water to stay hydrated in Morocco’s Sahara Desert. Photo: iRunFar

Meghan Hicks and Bryon Powell: are respectively iRunFar's Managing Editor and Editor-in-Chief. In 2016, they co-authored the book "Where the Road Ends: A Guide to Trail Running." Learn more about Meghan and Bryon.

View Comments (7)

  • Many of my 100 mile finishes or after three or more days of stage racing, I find myself becoming swollen. I’ve finished a couple 100s a few pounds up from my starting weight. I was never drinking excessively or purposely forcing myself to over drink in these instances. I’d imagine the swelling was due to third spacing due to an inflammatory response to the long events. If a runner notices they are becoming noticeably swollen while racing, do you have any advice? Thanks!

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    • Joel,

      Thanks for the comment and question.

      If you are noticeably swelling during the event itself, it's most probable that you are imbalanced in either water and/or electrolytes, and that means either too much or too little of one or the other or both. More often than not, it's overhydration that's the problem causer, though not always. I know that's a difficult answer!

      We have some deep-dive articles on hydration and overhydration that get into the mechanisms of this situation, https://www.irunfar.com/2012/08/waterlogged-part-ii-trials-questions-and-suggestions-regarding-hydration-and-ultramarathons.html and https://www.irunfar.com/2018/08/exercise-associated-hyponatremia-the-not-so-salty-truth.html. To be clear, these articles tend to focus on the extremes that can lead to true medical emergencies. An emergency is rare, but the physiologic responses/processes are the same for less severe circumstances.

      Each of us really is a study of one when it comes to hydration, though, and so it becomes a process of trial and error to find the hydration equation that works for you.

      Post-event swelling is different, like say, your event has ended and you're driving home that night or the next day and your feet become puffy. That sort of swelling can come from the same source as during-event swelling (residual hydration issues), from the event causing trauma to and leakage from the capillaries in your muscles and out into the space in between your cells (which is an expected part of rigorous and long bouts of running), and from the kidneys not performing well after the event (which is generally not good and can lead to a medical emergency). The experts tell us that while some post-event swelling should be expected after going for a day or three nonstop, we can minimize it via proper hydration during and after the event and training specifically for the event so that our soft tissues are as prepared as possible/will become less damaged by the event.

      I hope that helps! Thanks for reading.

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  • Thanks for the thoughtful response Meghan but I was hoping you’d say something simple like, “drink less water and take in more electrolytes when you’re starting to become swollen!” :) Unfortunately it’s not that simple. Hydration has many different recommendations that seem to change often. I’ve followed Noakes’s advice from Waterlogged for the last few years but a recent Koopcast has me thinking I’m hurting my performance by often not drinking enough: https://podcasts.apple.com/us/podcast/koopcast/id1489494447?i=1000477627145

    Thanks again!

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  • I used to "drink to thirst" on long trail runs, but my urine was always pretty dark when I got home, but I figured once a week of that was no big deal. Then, one time it was scary dark. So I certainly don't do that any more. Everyone's different I guess, but now I drink even if I'm not thirsty, and it's helped a lot (with performance, too).

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    • Hi TimR,

      Very interesting and thanks for sharing your experience! The scientific literature does consider members of the population like you, people whose thirst cues don't align with hydration status super well. We go into this a little it more in the book "Where the Road Ends," but it's not included in this excerpt as otherwise this article would be as long as a book chapter. ;-)

      The literature talks about some people with naturally delayed thirst cues, where the sensations of being thirsty come about when an individual is approaching dehydration instead of before dehydration. It was observed in these individuals, what represented a small number of study subjects, that they were more frequently water guzzlers than sippers, where they were able to ingest and digest larger volumes of water in shorter time periods and therefore able to recover their hydration status more rapidly.

      The literature also talks about people with thirst cues that don't match hydration status at all, and this has led researchers to speculate that thirst cues can be influenced by cultural aspects of drinking. As in, people from cultures where liquid drinking is a regular part of society may have altered thirst cues or recognition of them.

      You are probably a perfect candidate for some sweat tests, where you weigh yourself before and after runs of different length and in different temperatures to get a feel for your sweat-rate range/how much liquid your body goes through in your running.

      So interesting and thanks for sharing your story! You are a perfect example of how hydration really is an experiment of one.

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  • I am an avid trail runner and bike rider. I have always perspired heavily. I have found that I cannot go by thirst because my medication gives me a dry mouth all of the time. So have learned to take a sip every ten or fifteen minutes depending on the temperature and the degree of terrain difficulty. I am almost 61 and I have found my body is changing as well as to the amount of fluids to take until I hit a wall. I have been trying to adapt. It has also has been an experiment as to how much plain water versus how much electrolyte mix which is usually tailwind for me.

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    • Terry,

      Thanks for the comment and bringing up 2 unique variables in your hydration equation. Everyone's experience certainly varies and sharing our unique needs can only help others figure out their own hydration. Thank you again!

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