Wednesday, February 8, 2012

Hydration: How Much Do You Consume?

[Edit- this article is going to require more research.  As such, don't follow this advice yet.  :-)  ]

Figuring out how much liquid to consume is a topic of debate among runners. There are quite a few opinions out there, many involving a variety of formulas. I prefer to take a more individual approach- calculate your own needs. This is how I do it:

1. Before a run, strip naked and weigh yourself.
2. Go for a 5 mile run at your anticipated race pace without consuming anything.
3. Immediately after the run, weigh yourself (naked, of course).
4. Multiply your weight loss in pounds by 16, then divide by 5. That indicates the number of ounces you should consume per mile you run.

This is only a rough estimate and is dependent on training, temperature, and exertion level. Ideally you should drink enough to maintain body weight. If you're gaining weight during a run, you're drinking too much and run the risk of hyponatremia. Some weight loss is okay as slight dehydration isn't dangerous.

Other Measures

I do this five mile exercise occasionally to get a rough estimate of my fluid needs in conditions similar to race day. During races, I also use urine frequency and color as an indicator. In humid conditions, I know I typically urinate about once every 90 minutes and it looks like light yellow lemonade. In dry conditions, that time extends to about 120 minutes. In 100 milers, I've also brought a scale along to make sure I'm not gaining weight.

What About Drinking When Thirsty?

Many people use this method, and it usually sucks. Thirst is rarely an accurate indicator of hydration status. In my experience, most people over-drink if drinking when thirsty. Furthermore, the fatigue late in races tends to mess with your sense of thirst.

One last tip- lay off the ibuprofen. It messes with your kidney function. If you need pain medication to get through an ultra, you probably need to do a little more training.



  1. Jason, I generally agree with what you write. However I am wondering if this post is a joke?

    "Ideally you should drink enough to maintain body weight" goes against all good advice I have ever read and recommended. If you are consuming a bunch of solid food, then maybe I can see maintaining weight with the help of the food. But while running I never use solid food, it's all liquid and a bit of gel. I feel like maintaining weight would be very difficult for me to do on 15+ mile warm runs.

    And I believe thirst is a great indicator of hydration honestly and what I have used throughout all my training and races.

    1. Kyle- check out some of the research done at Western States. They have what could be considered the best collection of ultrarunner data regarding hydration. That's where I got the basic foundation of my hydration strategy.

      As far as thirst, most people tend to over-drink in races if using that as a measure. Check out Noakes' stuff about hyponatremia.

      Over the course of a typical ultra, a few pounds of weight loss is expected. A huge weight loss is bad, as is a moderate weight gain.

  2. Kyle- here's the WS stuff:

  3. And here's a Fitzgerald article quoting Noakes:

    1. Does not this entire article go against what you said above?

      Matt says: "You've probably been told to drink enough fluid during exercise to completely make up for what you lose through sweat. In other words, the goal is to weigh the same before and after your workout. But the latest research has revealed three problems with this advice."

      And you said, " Ideally you should drink enough to maintain body weight."

      You recommended exactly what he is attempting to explain as incorrect.

      Jason: "As far as thirst, most people tend to over-drink in races if using that as a measure. Check out Noakes' stuff about hyponatremia. "

      Matt: "by thirst (roughly 13 oz. per hour), at a moderate rate (about four oz. every 15 to 20 minutes), and at a high rate (about 10 oz. every 15 to 20 minutes)."

      The people who drank by thirst drank the least amount of water. Two of the high rate people could not complete the workout. That is consistent with other studies I have seen showing the individuals who drink the most are at the most risk for hypoatremia and not completing the event. It is nearly impossible to drink too much if you are drinking by thirst.

      I apologize if I am misunderstanding something here...

  4. Hmm, I thought you cannot rely on thirst because such way you drink too little, not too much.. Because as I have heard - if you are thirsty, it's already too late.

    Also, I wanted to clarify - if performing this experiment with 5 miles and weighting before and after that, do I weight myself with all the sweat on my skin after the run or do I wipe it all off first? I guess, the sweat could either evaporate on a race day if it is very hot, or it can be absorbed back through skin if it is not so hot.

    1. Guess who first said thirst was too late? Same people who originally recommended to drink as much as possible. The people selling the sports drinks, of course.

      I would recommend you wipe it off. But I would also recommend to drink by thirst...