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Running Tip: The Importance of Hydration

By , SparkPeople Blogger
Hydration is something many of us take for granted, but it is even more important the more active we are. Water is one nutrient we cannot, nor should not forgo. While we can go for weeks without food, water is a whole different scenario. Without water, death can occur within days.

So why is hydration so important when it comes to running?

Water acts as a coolant when you are exercising. Think of the water within your body as the anti-freeze you put in your car. Sweating is the involuntary response that keeps your body from overheating. When you begin exercising your body's temperature begins to rise, this in turn triggers your brain to signal your sweat glands to increase sweat production to speed up the cooling off process.

Because our bodies are comprised of 40-70% water, just a slight shift in the body's fluid balance can lead to drastic changes in our running performance. Sweating accounts for well over 90% loss in water during a run--add warm temperatures and humidity into the mix and this rate can go even higher. The remaining fluid loss comes from our breathing as well as urine and feces production.

Keeping tabs on your hydration is essential to getting you through your run. Click here for hydration guidelines while you are working out.

Dehydration is defined as losing more fluid than you have taken in which then can affect normal body functions. It can lead to many changes in the body including the following:
  • Fatigue
  • Dry mouth
  • A decrease in sweat rate
  • An increase in heart rate
  • An increase in body temperature
  • A drop in blood volume which can lead to a drop in glucose being transported to the muscles to use for energy
  • Nausea/vomiting
  • Drop in urine output
  • Cramps
  • Chills
It has been reported that for every 1% drop in body weight from fluid loss, there is a 2% drop in your running performance. This may not sound like a lot of weight, but for a 120-pound runner a weight loss of 3 1/2 pounds can lead to a 6% drop in running performance.

Factors that can determine our sweat rate include:
  • Ambient or air temperature. The higher the temperature there is an increase in sweat production. But note that even in colder temperatures, the body will sweat, but at a much slower rate.
  • Humidity levels-The higher the humidity, regardless of the ambient temperature, the more difficult it is for the sweat to evaporate off the skin making it harder for the cooling off process to take place. If you notice sweat rolling off your skin, this is an indication that you need to stay on top of your hydration.
  • Wind speed-The higher the wind speed the greater cooling-off effect so that sweat production may be lessened. Calm days may lead to an increase in your sweat rate.
  • Body conditioning-The better conditioned you are to a particular activity, the greater the sweat volume, so you will usually begin to sweat sooner into your run.
  • Gender- Men tend to sweat more than women, not only due to their bigger size, but also due to their increase in muscle mass.
  • Genetics- We are all the product of our ancestral genes, therefore, some individuals sweat more profusely than others, even when not exercising.
  • Wearing inadequate clothing-It is important to dress as though it is 20 degrees warmer than the actual ambient temperature. In other words, if the ambient temperature is 55 degrees, you will want to dress as though it is 75 degrees-- usually this means shorts and a short sleeve wicking shirt. You may be a little chilled in the beginning of your run, but within a few minutes, as your body's core temperature begins to rise, so will your sweat rate.
It has been reported that most runners have no clue as to how much water they lose during a run. This is where determining your sweat rate is essential as to how much you need to drink following a run.

Determining Your Sweat Rate
  • Determine a baseline weight by taking your average weight over the course a normal week
  • Weigh yourself without clothes and shoes before your run
  • After your run, remove all clothing, dry off well including your hair if you are a heavy sweater, and weigh yourself again
  • For every pound you lose, you will want to slowly re-hydrate with 16 ounces of water
For example if you lose 3 pounds during your run, you will need to rehydrate with 48 ounces of water, slowly over the course of the day. This is in addition to what you would normally drink.

In rare cases, if you find yourself at a weight greater than you were before your long run be aware that you may have over-hydrated. Drinking too much can be just as serious as not drinking enough. Too much fluid can lead to a condition known as hyponatremia. This condition generally occurs on training runs well exceeding two hours in duration where a runner is drinking more than they need.

According to data reviewed from various marathons from around the world, women are more susceptible to this condition because of our slower marathon times, lower sweat rates and our tendency to stop more frequently at the water stations.

For many runners, hydration is the difference between a great run and a not so great run. Educating yourself is what will allow you to find the proper hydration balance for you. Some runners find that drinking a sports drink with electrolytes added can help keep the body's hydration in check.

Have you ever determined your sweat rate to help with rehydration later in the day? Have you ever experienced symptoms of dehydration and/or overhydration?

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CECELW 4/9/2021
i'm definitely not a runner. I'm kind of glad this doesn't apply to me Report
GOFORGIN 3/7/2021
Ok Report
USMAWIFE 9/29/2020
thank you Report
Great information. Thanks. Report
While I am out walking in the hot sun, I have had several people to offer me water. Report
Interesting Report
I don't drink much as I never seem to get thirsty. The first I know is when I get a headache

I like this blog, especially what follow dehydration and how to calculate our sweat rate. I think we can use the sweat rate for other exercises, too. Will extract some of these info and put into my blog and my fitness plan book, as a reminder :) Report
I don't waste money on buying water, as I've seen so many reports about how it really isn't even any more than our good tap water. Report
Thanks for this very useful information! Report
I drink 3-4 32-oz. bottles of water daily. I only run 3 miles 3x per week, so although I do drink 8 oz. prior to running, I don't drink DURING my run (35-38 minutes long). I do drink 8-20 oz. over the course of the hour after my run is finished. Report
Wow. I never thought about the science of hydration. I have an ileostomy, so when I begin to sweat, I am very conscious of fluid intake. Thanks for this info. It's really interesting and practical. Report
Thanks coach Nancy! I was wondering why on some runs I start to get the chills toward the end. Now I know! I do drink a lot when I have a normal work day - keep an 2.2 L jug at my desk. But if I'm up away from my desk a lot or, at home on the weekend I tend to drink a LOT less - redoubling my efforts to maintain throughout the week no matter what. Report
Recently started reading the various Water books by Dr. F Batmanghelidg - info is at his website / - and I've noticed less of a tendency to have hyponatremia since using good quality unprocessed sea salt (not white bleached table salt). It also doesn't affect blood pressure or cause the swelling from "too much salt" the way I get when I've had too much overly processed high-sodium junk foods. Very cool, and I feel better when I do exercise!! Report
Drank MUCH more water than usual today, as I was outside working in the heat all day. Usually drink 8 to 10 cups a day, probably doubled that, today. Report
A friend of mine got hyponatremia on a strenuous bike ride - and it was almost life threatening. The hospital almost made a serious mistake - they initially thought she was dehydrated. But fortunately an alert doctor realized the difference and they got her stabilized. Now she drinks electrolyte fluids on long rides. Report
I really make it a point to drink a gallon per day. Report
People who do Bikram yoga should pay close attention to this. Many Bikram yoga instructors will allow students to drink water ONLY at certain times. They basically prohibit water drinking except when they say it's ok. This is contrary to Bikram yoga guidelines; it is also very dangerous. While being considerate of those around you, you must take care of yourself and drink when you know you need it. Report
Many seasoned runners will push through their need for hydration. Many of us become accustomed to pushing ourselves. This is what gets many runners into trouble. Report
By the time you're thirsty, you're already on the verge of dehyration! Even constipation which is not on the list and water helps in so many ways! Report
I've had to start slow with aerobic workouts because I had to recondition my body to sweat. I had several instances of near heat exhaustion in the process. I celebrated the day I worked out and attained a full dripping sweat; it told me I was getting into better shape. Now I'm looking forward to getting some under armor! Yeah Sweat! Report
Oh, I had to learn my lesson the hard way. Yes, I have experienced dehydration on more than one occasion. One time was in a kick boxing class. I figured I'd be "tough" and wait til the end of class to drink. that was a very bad idea. by the end of class, I was borderline passing out.

Another time, I was running a 10K during warm weather and ignored the water stations. Yet another bad idea that led to dehydration. These days, I always travel with a water bottle and I always make sure I am well hydrated.
This is great for me to read today, as I'm about to head out for an hour long run in beautiful 65F weather... thank goodness for my camelback! :)

I also didn't know that you sweat MORE when you're conditioned to a sport! That explains why I was sweating after a 30 second sprint for the bus the other day, when I never used to sweat before I started running regularly! Report
I really must drink more water. I seem to have a problem doing that. I do drink juice, milk, etc. but maybe only one big water cup a day. I know I'd feel better, if I drank more. time to start that. Report
Great info to know. on to my exercise. Report
Great blog!!
I try to drink at least 2 cups before my run, and will do an "Energy Bar" gel along with another cup right before I start. I drink along the run, but sometimes fall behind on the amount, trying to do gels every 30 minutes with water to keep the electrolytes in check. Very true in performance vs water. Keep the good "tips" coming---Disney is coming quicker than you think. Report
Great information. Report
I can't run so no worries for me... Report
I am terrible at hydrating during a run. I really hate drinking while running. It makes my tummy feel funny. Maybe I should try a sports drink over h2o. I get dry mouth a lot when I run, but that's about it. I do drink before and post run. I haven't ever "officially" done my sweat rate, but I do know I lose about 2 lbs on a long run... Hmmm... should spend more time figuring this one out.... don't want to lose 4% performance... Report
I haven't yet determined my sweat rate. I know my sister does, but not to find out how much water to drink -- she just wants to see her weight go down (not the healthiest mind set, if you ask me). Even though I haven't done the sweat-weight-test, I know that I drink a LOT of water throughout the day, before my runs, and after my runs. I'm thinking about investing in a hydration belt too, because while I hate carrying a water bottle with me, I really prefer to be able to drink during my workouts. Report
Thanks for bringing our attention to an important subject Report
I have found one of the most HELPFUL things on my hikes, is sipping water constantly. Makes such a difference in my endurance. I discovered this a while back, and consequently, have to take more water at times to make it up some of the hills I have climbed! Report
wateer is a key to better taking care of yourself. Report
Being diabetic, stomach cramps, dizziness, dry mouth are signs that I am already dehydrated,, I drop whatever and run to the nearest water source,, room temp water is important, to avoid worse cramping,, Report
It might be useful for reader to know that water weighs 8 pounds per gallon. Thanks for the article. Report
This article appears just as my electrolyte test came back abnormal. Now I'm wondering if a 12 hour fast (no food, lots of water) followed by a several mile run had something to do with it.

I've definitely experienced dehydration. Overhydration would be a new one for me. Perhaps it's time to be more systematic and measure. Thanks Nancy! Report
I habitually underhydrate, and now that I've begun an exercise program, it's important that I become aware. It's interesting how not hydrating enough causes one to retain water. Report
Good information to know especially living here in South Florida where it warm all year round. Report
I'm glad I read this article. This has already given me something to think about for my next run Report
Liked this blog.
I am glad you also said something about overhydration. I think lots of runners don't take his into consideration.
Sometimes I also take an e-cap to help with the hydration getting into me. Salt and electrolytes are real important in running performance. The lack of these will effect how you run. And depending on how far, a gel or two. However, after about 20 miles all nutrition becomes more difficult for me. Report
That was so informative ! I just know that I have to drink a large glass of water when I come home from the pool, work in the yard or house or any other kind of exercise. My body tells me. Guss I need to get more scientific.
Great Blog ! Report
I keep thinking I need to do the sweat rate test, but I usually forget until I"m already running! I'm going to try and remember this week. I think my race last week, I was hydrated correctly - but it would be nice to know what I should be taking in after I'm done!

Thanks for the great blog Nancy! Report
I guess I've always taken hydration for granted. I haven't determined my sweat rate (though I think I sweat a lot, very salty as well) but I just drink what seems right to rehydrate. The only symptoms of dehydration I think I have experienced are fatigue and dry mouth, but maybe I should take a closer look! Thanks for this blog! Report