Hydration- A lesson in interpretation

I’ve used the example of hydration during running to demonstrate the natural cycle of under/over emphasizing until we kind of naturally move towards the sweet spot. What I’d like to do now is use hydration as a way to show error in interpretation.


When we rely on scientific data, we tend to look at the conclusions as fact. After all, most people simply peruse the abstracts and jump straight to the last one or two sentences that basically say what the heck the article was all about. Even if we browse the article, we often skip the methods and the results section which tells what they actually found and head straight towards the conclusion statement where the author’s give us a “what does this mean practically.”

Problems arise when we interpret the conclusion as exact fact. Instead, it is the data that should be factual and relevant if the experiment was done correctly, and the conclusion is left for human interpretation and error. I’m not saying that the author’s concluding remarks are false or useless, as they often provide great insight. My point is that even the best and brightest of us make mistakes in interpretation and that’s when we run into problems.


It’s not the science or the data that is the problem. It’s often us.



Human interpretation is faulty:

Hydration provides a perfect example of when we take good data and misinterpret what it is telling us. Way back in the early days of marathoning and exercise science, some early pioneers took some data and found that there was a direct correlation between weight lost during the marathon and the finishing speed of that runner. Put simply, the faster runners lost more weight during the race. The data was right on.


The human interpretation wasn’t. Seeing this data, the conclusion at the time was that it was bad to drink water during a marathon. It seems logical enough right? The faster runners lost more weight and thus didn’t replenish their fluids as much, so taking water to maintain fluid loss most negatively affect performance. So for several years, the prevailing logic was that in order to maximize performance, runners should not drink. After all, there was a direct correlation between weight and water lost and performance!


When health became more important than performance and some more data come out that dehydration was a bad thing. We overreacted and decided to push full weight maintenance during the marathon, which resulted in a lot of problems, such as a huge spike in deaths related to drinking way too much water (Hyponatremia). This isn’t a post about that cycle but you need to know that to set the stage to where we are today.

Hydration today: Fastest runners still lose the most weight/water

Which brings us to today. Alex Hutchinson does a nice job summarizing the latest research, which not surprisingly found the same results that were noticed over a half century ago. (http://sweatscience.com/hydration-faster-marathoners-lose-more-weight/). Today though, we interpret the results differently. It’s essentially the same data, but the conclusions are remarkably different: We should simply drink to thirst. It’s okay to be slightly dehydrated at the end of a marathon. The key is listening to your body and figuring out where that sweet spot of consuming enough fluids versus forcing fluids down is.

One interesting thing about all of this is that it demonstrates how we easily can override our own body’s feedback signaling just because of the way we think and what we’ve been taught. Essentially, if we are inundated with the importance of (over) hydration enough, then we’ll ignore the thirst or fullness signals our body might send.

What do we take away from this example and the interpretation problem?

Well the simple answer is to drink to thirst. The complex answer though is that it might have been so long since we’ve paid attention to our thirst mechanism that it’s going to take some practice and adjustment. Which leads me to one a quick tangent: Paying attention to feel or running by feel is great, but it’s a skill most of us have to relearn. One of my former HS guys (who is just ran 14:26 for 5k for Texas! Congrats Will!) told me last week that it took him almost 2 years to figure out how to do a threshold/tempo run correctly. Even with emphasizing the importance of running by feel, and banging the concept into his head a million times, it took him 2 years to be self disciplined enough to stop letting his competitive instincts of running with some of the other guys like Ryan, take over and block the feedback he was receiving while running.  Part of it was my fault because I was spending too much time making sure the (at the time) better and older guys like Ryan, Jeremy, and Cody were getting it and there was only one of me to run with everyone, and an at the time over 5min miler as a freshman didn't get as much attention as he should have!

On the science side of things, the lesson is a little more subtle. Instead of browsing the author’s conclusions on research, look at what the research actually found. Look at the actual results first, think critically, and form your own quick opinion before reading the Author’s remarks and interpretation. This way you’ll at least avoid falling into the trap of simply relying on others interpretation. If both you and the author’s interpretation matches up, you’re probably on the right track. If it doesn’t, then I wouldn’t jump right into whatever the research claims. Additionally, after reading the research, think if you could interpret the data in another logical way, just as the hydration data could be seen from two different viewpoints that were both seemingly logical at the time.

The data is seldom wrong or off, it’s just us humans that get in the way of it.

6 comments:

  1. Nice post!

    It's a huge problem that people will make wild conclusions from relatively benign data, and those conclusions are the ones that are often taken and run with (no pun intended) by media outlets and the like.

    This is certainly a subject I will continue to pay attention to as I go on in my career!

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  2. Anonymous9:34 PM

    Great post

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  3. Nice post. The topic of water intoxication and hyponatremia is complex, although today the issues are becoming more clear.

    In 1969 a study by C.H. Wyndham and N.B. Strydom entitled "The Danger of an Inadequate Water Intake During Marathon Running" (in the South African Medical Journal) may have been one of the triggers for new water recommendations, influencing international rule changes that would allow fluid intake—water stops—during endurance races.

    In 1985, Noakes and colleagues published a groundbreaking research paper in the journal Science and Medicine in Sports and Exercise, which described the occurrence of water intoxication, too much body water, and hyponatremia, abnormal blood sodium levels. But by then, Gatorade and other sports drink and water companies were big players in the endurance world, sponsoring many athletes and races—marketing now played a role in contributing to serious medical conditions in athletes.

    In a 2004 study of Ironman triathletes published in the British Journal of Sports Medicine, Karen Sharwood and colleagues concluded that, “There is a large body of literature that suggests that dehydration impairs performance and increases the risk of heat illness in ultra-distance races. However, these conclusions have been based on laboratory studies using exercise interventions of relatively short duration and are thus limited in their application to performance in the field.” Sharwood’s study was performed during the 2000 and 2001 South African Ironman Triathlon, and showed that there was no increased risk of heat illness associated with high levels of dehydration, and that high levels of weight loss do not significantly influence performance.

    In fact, in some endurance events the top finishers showed some of the greatest loses of weight associated with dehydration. However, it’s impossible to say how much better any given athlete would perform without as much water loss. And, it can also be shown that even mild dehydration can impair muscle function. So the issue is not so simple if one wants to give general recommendation for all athletes.

    The sensation of thirst appears after a certain degree of dehydration, and this was always interpreted as meaning thirst is not the best indicator of fluid needs. In hindsight, this may indeed be the best indicator if mild dehydration is not an issue during competition.

    In a study compiling 2,135 endurance athletes who completed 42-kilometer marathons, 109-kilometer cycling events, and 226-kilometer Ironman triathlons (Proceedings of the National Academy of Sciences, 2005), Noakes found that about 60 percent were dehydrated while 11 percent were overhydrated. Overall, 6 percent had mild hyponatremia, and 1 percent had severe hyponatremia.

    What is simple is the concept of self-health management. It’s quite possible that those who develop water intoxication and hyponatremia may have reduced levels of health to start with, making them most vulnerable to these problems. This is often related to a problem in the HPA (hypothalamic-pituitary-adrenal) axis, the brain-hormone control of fluid, water and stress.

    Athletes should take control rather than let the sports drink market set the pace of fluid recommendations. Athletes should learn the optimal way to hydrate during a long race—drinking about the same amount of water that’s lost—and avoid using sports drinks as everyday beverages. Along with avoiding overtraining, and eating a proper diet, improvements in overall health helps assure proper hormone balance to better regulate water and sodium on race day—which can also contribute to a better performance.

    Phil Maffetone

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  4. As a follow up to my comment on Steve's hydration article, I've now finished my article on water intoxication and hyponatremia. It's listed on my home page (www.philmaffetone.com).

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  5. Always drink a substantial amount of liquids to keep your body hydrated.

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