Slowing to a trickle: The importance of hydration

I learned several important lessons on my 20 miler this week.  The first, of course, was to review the course and it’s elevation before setting out.  The second was the power of hydration.

I left for the run with my fuel belt and two small bottles of water, intending to loop back past my parent’s house to hydrate and refill my bottles.  When I missed my turn, I knew it meant I would have to last through the whole 20 with minimal water.  Although nothing terrible happened, I learned first hand the effects of dehydration in a way I don’t think I’ve ever experienced before.

Not nearly enough for a three hour run

I was well fueled and my legs felt fine.  However, my pace dropped off those last few miles, and I knew it was related to my poor hydration.  I had recently read the chapter on hydration in Advanced Marathoning and was remembering these words:

Studies have found that dehydration of 2 percent of body weight leads to about a 6 percent reduction in running performance… This is because any reduction in blood volume will reduce the amount of blood returning to your heart.

…It’s not unusual to lose 3 pounds of water per hour when running on a warm day….For a 140 pound runner, this would represent more than a 4 percent loss of body weight and more than a 12 percent decrement in performance.

The effect increases as the run progresses, so this runner … would likely slow by up to a minute per mile by the end of the run.  Staying well hydrated, then, can be the difference between training hard enough to provide a strong stimulus for your body to improve, or just going through the motions in training and never reaching your potential.

I was slowing down by about a minute per mile on those last few miles, partly wondering if I had made the right turn to make it home, and partly because my body was telling me it was done.

As you become dehydrated, your blood volume decreases so your heart pumps less blood with each beat and you produce less energy aerobically, slowing your pace.

Working my way up to one of these per hour

How much should you drink?

Most sources suggest four pints per day, with additional fluid to make up for that lost through exercise.  During a run, you should drink only as much as your stomach can empty, or a max of 24 ounces per hour.  I rarely drink anywhere near that amount, but this week’s run reminded me that I cannot overlook the importance of staying well hydrated.

Advanced Marathoning reports studies that have found racers drink less than 16 ounces of water per hour, and lose an average of 3.2 percent body weight during a marathon.  This can translate to a loss of more than 9 percent in performance.  So the average marathoner may race slower than his/her potential due to progressive dehydration.

Many sources, such as this article, confirm that consuming a drink with carbohydrates can substantially increase your chances of reaching the finish without running out of glycogen.  Using gels, chews or other easily digestible snacks is another alternative.

Although staying hydrated may not make you run faster, being poorly hydrated will definitely slow you down.  Now I have a few more long training runs to get it right before race day.

Do you have a long run hydration plan? Have you ever experienced the effects of slight dehydration?

26 thoughts on “Slowing to a trickle: The importance of hydration

  1. I loose a large amount of fluids when I run and am one of those people who has to drink a large volume of fluids on my longer runs. In fact, many times I wonder if this is why I haven’t done well in a few of my marathons. I think I’m drinking enough, but I need more for these longer distances and the warmer it is the more you need. Nice article Laura! Have a great weekend
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  2. I run with a Camelback on my long runs so I always have access to water. Then I chug water when I get in the door. My problem lately as it gets cold out is that drinking water makes me so much colder, even after a shower and it deters me from drinking. Need to find a way to remedy that…
    Amy @ Writing While Running recently posted..Home Sweet HomeMy Profile

  3. If my husband isn’t riding his bike with me I will loop back past my house for refills that I put in my mailbox. Sorry that you missed your turn. I always get nervous running in areas that I am not that familiar with.
    Tasha @ Healthy Diva recently posted..DIY Sparkle SkirtMy Profile

  4. I always try to carry more than I think I will need or plan a route to pass fountains. It is tough when you get dehydrated. I had this issue last winter when my water froze and I was stuck about 5 miles from home and already 10 miles in without water, ugh!
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  5. Good post! The information regarding amount of hydration is interesting. I actually have been running for over a year now with handhelds myself. I use different sized ones, depending on the distance I plan to run. I prefer the Amphipod brand because I has small hands so getting them around a ’round’ bottle isn’t as comfortable on the run compared to the more ergo Amphipods. I was never able to get used to all of that around my waist. I have always been the type to want some liquid on any run. Even if it is 3 miles, I tend to get ‘parch mouth’ and like a little sip of water here and there. What that has done is actually always keep me well hydrated. I don’t drink a whole bottle obviously, but I like to have it along for some sips when I feel I need it. With longer runs, I usually end up drinking most of the bottle by the end. If it is hotter out, it goes faster 🙂
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  6. I was dehydrated and salt depleted after I finished my half in the Spring and I suffered severe cramping for many many hours afterward trying to get things back to normal. I thought that I was drinking lots of water and nuun too… apparently not enough for ME on that day.

    Good information here, so important.
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  7. I still need to work on this especially now with colder temps. The last thing I want to do is carry a water bottle! But I have noticed the difference. My last 10 miler I didn’t have anything. I felt slow and drained at the end. Plus I didn’t pee for almost 2 hrs after I was done. Totally dehydrated! Great tips!
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  8. I’ve definitely felt the effects of not drinking enough water – pretty certain that’s what kept me from my sub-3:40 finish at Gansett last year. It’s good that you didn’t get truly dehydrated, but also kind of good that you experienced some of those effects – makes for a good learning experience – and so much better to have it happen during a training run, rather than on race day!!!
    Michelle recently posted..Philly Marathon WeekendMy Profile

  9. I use my Camelbak Flash Flo belt pack which works wonders and has a nice zipper pocket for GU or Honey Stingers or whatever. I have had to plow through dehydrated a couple of times (my old hydration pack apparently had a leaky bladder and I didn’t realize it the first time since I was sweating a lot) and thankfully I didn’t have far left on my runs to go. But I won’t forget that feeling of weakness and mental fog. It’s scary!
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  10. I have no plan. I tend to vacillate between overhydrating in races to dehydrating myself during training runs. Solid! My coach told me to stop running with my fuel belt because it’s not good for my back, so now I try and plan my runs to where I have a water fountain every 2.5-4 miles. It works out fine on cool days, but I’ve definitely bonked on long runs during warm days. Hope you figure out something that works for you!
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  11. I live on the coast of Alabama. The summer here is around 90-100 degrees with a heat index of 100-115 degrees and 100% humidity. Dehydration is a major issue down here. I have to hide water bottles on the trail I run to try and stay hydrated.

    I suffered from major de-hydration one time and learned never to let that happen again. My pace slowed down from 8:45 to 12:00 minutes on a 12 miler. I was physical ill for hours afterward.

    Great article, Thanks
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  12. Hey Laura, I just read your post about infertility struggles that was linked in your recent 5K recap. Thanks for sharing those thoughts. I have been dealing with the same thoughts and feelings that you described. Also, congratulations on your 5K PR!

  13. I definitely do not hydrate enough during long runs. Something I really need to work on. I think I do a pretty good job during races, though. I have a hydration belt, I just need to use it.

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  15. Great post! This has been one of the great things about doing all my long runs with a group that puts hydration on the trails. I still wear my belt and top off my bottles at each stop.

    This “off-season” training for Goofy has been challenging because of the hydration issue. I’ve been planning shorter loops than the full distance to allow for hydration refills, and am very thankful I have!
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  16. I know what you mean about the slowing down due to lack of water. I don’t really eat a lot of gels or gus, but I do always carry water with me, even for shorter runs or runs where I know there will be drinking fountains on the route. I think another thing people forget is that when it’s cold, we still lose the same amount of fluid, but we don’t seem as thirsty so we don’t drink enough.
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