Hydration: The Facts — and the Myths

May 22, 2015

Running expert Nate Vandervest offers some helpful tips on hydration:

Whether or not you’re a runner, you have certainly heard the stern advice: Drink lots of water. Stay hydrated.

And while it’s true that a person should consume liquids both throughout the day and during a race, the question remains: How much? I’ve looked into the research on this subject to get a better handle on the facts surrounding the dreaded dehydration.

I hear it all the time: “My race/game didn’t go well because I was dehydrated.” Heck, a few years ago I used the same excuse for a horrible run at a very hot Boston Marathon. What I started to realize is that it’s easy to blame poor performance on dehydration — rather than, say, poor training or a lack of consideration for the weather. Dehydration is an easy excuse because most people don’t understand the body well enough; they just go along with it.

As many of you know, the body isn’t that simple. It is a very complex system of checks and balances that work to ensure everything functions properly and efficiently.

Humans sweat, and some of us sweat a lot! Sweating is a perfect way to stay cool but it takes a lot of water to do so.  We sweat so we don’t overheat. Most people exercise comfortably at a body temperature of around 100 degrees.  If that goes up to 104 degrees, we will likely be seeing you in the medical tent — and anywhere beyond that, you are in serious trouble. 

So say it’s a hot day and you’re a heavy sweater. You should probably drink a lot of water while out on your run, right? Not so fast; there are a lot of factors involved:

First off, how hot is it? The hotter it gets, the more you need to adjust your pace. Overheating is your main concern, and it will cause problems well before you’re dehydrated to the point of needing medical attention. 

Second, how long is your run? Longer runs are usually done slower, which means you don’t produce a lot of heat. This, in turn, means you don’t have to sweat as much. For any run longer than an hour, you should bring liquid. For anything under an hour, as long as you start hydrated you should be just fine.
The body can absorb about 20 ounces of liquid an hour, depending on the person. Some of you may be thinking that you sweat way more than that in an hour, and 20 ounces of liquid won’t replace what you’ve lost. You’re exactly right. 

Remember what I said earlier about the body being complex and keeping itself in check. Well, the body goes into a “voluntary dehydrated” state and works really well by doing so. You should lose a few pounds over the course of a run; this isn’t a big deal and your body will get back to normal by the end of the day. Our bodies know how much water “reserve” is left and how much “salt” can be eliminated while sweating. Sweat rates and the salt content in them vary from person to person and even within the same race or training run. If your body needed that water or salt, it wouldn’t let it go as sweat.

One of the reasons we drink so much is that in 1996 the American College of Sports Medicine stated that athletes “should drink as much as tolerable” or 20 to 40 ounces of liquid per hour.  This statement coincided with the second running boom and came at a time when more and more people wanted to run marathons.

Unfortunately, this collection of circumstances led to people getting sick — and in dozens of cases, dying — due to over-hydration (hyponatremia). It is worth noting that in this same timeframe there was only one scientifically recorded case of someone dying from dehydration during an endurance event.

Old habits die hard. Since 1996 we have learned a lot more about over-hydration, and yet the public still promotes the “drink as much as possible” theory. 

So what should a person do? Consult with a professional who can help you with current guidelines and recent research. Next, drink when you are thirsty and you will be just fine, contrary to whatever article you may have read stating that by the time you are thirsty you are already dehydrated. Remember, your body is smarter then you give it credit for, it will let you know when it is thirsty, hungry or tired. You just have to listen. 

During competition, around 20 ounces of liquid per hour is enough. During short races (5K or 10K), use the water stops to splash your face or back of your neck to cool off. Drinking liquid will help, but if you started the race hydrated, you will be fine. Hydrate properly the day before an event. It shouldn’t take much effort to get some additional liquids in you. No need to hydrate for half a week prior — this will just have you running to the bathroom more often.

Nate Vandervest, CSCS, CES, is a running coach and strength coach who specializes in running assessments, strength training and personalized running programs. For more information contact Nathan.Vandervest@bellin.org.

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