Asker Jeukendrup on Gatorade and Geb

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As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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While I was in New York earlier this week, I had a chance to chat with Asker Jeukendrup, the new “global senior director” of the Gatorade Sports Science Institute. After Amby Burfoot’s wide-ranging interview with him in September, I was curious about what that would mean both for his research and for Gatorade — which, as I wrote about in a Globe article back in 2009, had seemed to be moving away from evidence-based science and toward marketing gimmicks like adding theanine to “improve focus.”

So, after our conversation, I’m now at liberty to reveal… well, nothing. Asker promises that the Gatorade formulas will change, possibly in the short term but certainly in the medium term as new research directions yield results. What those research directions are he wouldn’t reveal, but he emphasized a shift from hydration to the full spectrum of performance nutrition. Two key focuses: energy delivery and recovery. What does this mean? His previous work on “multiple transportable carbs” (which he made famous for PowerBar) showed that the bottleneck for athletes trying to get carbs to their muscles is getting the carbs across the intestinal wall. My totally uninformed guess is that he’s looking at novel ways (different types of carbs? different molecular structures? different ratios?) of getting carbs across that barrier more quickly.

One other interesting nugget. A few months ago, I blogged about a study that included an unverified claim that Haile Gebrselassie lost 10% of his body mass due to dehydration during his world record marathon run. Jeukendrup has worked extensively with Geb — and though that data is confidential, I pressed him a bit about this claim. He confirmed that the 10% figure was reasonable. Geb’s a very small guy who’s capable of working at an inhumanly high work rate for an extended period of time. The result: he generates a huge amount of heat, and thus sweats a lot, likely more than two litres an hour. It’s not practically possible to drink anywhere near this much at world-record marathon pace, so Geb loses a ton of weight.

So the obvious question is: does this rather severe level of fluid loss hurt Geb’s performance? Jeukendrup’s guess: no. The primary mechanism through which dehydration might hurt performance is through reduced blood volume forcing the heart to work harder. But you can compensate for reduced blood volume to some degree: for example, your veins (which return the oxygen-depleted blood to the heart) contract, effectively shortening the circulatory loop. Geb’s example doesn’t prove anything either way — obviously it’s possible that he’d be a 2:02 guy if he drank more. But it’s hard to argue with a world record, unless we have some compelling reason to think that dehydration held him back (and I can’t think of one).

Dehydration in the lab vs. the real world

THANK YOU FOR VISITING SWEATSCIENCE.COM!

As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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The “right” amount of hydration during exercise is a hot topic these days. For years, lab studies showed that if you forcibly dehydrate someone and then stick them on a treadmill, their performance suffers. But more recently, “real-world” studies (like the one I blogged about here) have shown that in many cases, the fastest finishers in races tend to be the most dehydrated. The difference, according to researchers like Tim Noakes, is that in the real world your brain is able to make pacing decisions that keep your body in a safe state (using the thirst mechanism); on a treadmill at a fixed pace in a lab, your brain is cut out of the loop.

The result is that there are two bodies of research — lab and field — that appear to be answering the same question (how much should we drink?) but that produce completely different answers. So it’s nice to see a study from the “lab” camp that tries to bridge this gap by doing some experiments on an outdoor trail run. Researchers from the University of Connecticut had 14 runners perform two 12K trails runs, one in a hydrated state and the other in a dehydrated state. Here’s what they found:

Pretty straightforward, right? The runners were slower when they were dehydrated. As expected. Case closed. And we should disregard those inconvenient studies that found that faster runners in real races are more dehydrated, according to the researchers:

Although some field studies have found runners to be extremely successful despite considerable body fluid losses, these runners were not compared with a control condition where these same runners remained more optimally hydrated. Therefore, one cannot conclude that performance in these elite runners may have been enhanced if they had maintained or at least attenuated some of their fluid losses while racing.

But hang on a sec. Does this new study really offer valid “field” conditions? Not quite. It may have been conducted outdoors, on nice trails in a local state park, but it nonetheless managed to reproduce all the usual problems of lab studies. First of all, the runners weren’t freely paced: they were instructed to run at a set heart rate, which imposes a rather arbitrary limitation. So they didn’t go slower because they were unable to keep the pace, but because they weren’t allowed to increase their heart rate. More importantly, the dehydrated runners weren’t allowed to drink or eat “high water content foods” for 22 hours before the test run! The result:

So what can we conclude from these results? If you subject volunteers to a punishing dehydration regimen before your experiment even starts, their performance will suffer. This is very important to bear in mind next time you’re stranded in the desert. But as for how much water you should drink during your next run, this study has basically nothing to say.

(I should point out that the researchers did measure a number of other physiological parameters in the study, like gastrointestinal temperature. This is useful data. They also argue that holding heart rate steady is useful because it’s “similar to how a cross country or track coach may advise their athletes to maintain a certain intensity level during a run.” Sure, I guess. But if that’s what they’re measuring, then why are they using the results to make claims about what happens in real-world marathons, where nobody starts after a full day of dehydration?)

How quickly is water absorbed after you drink it?

THANK YOU FOR VISITING SWEATSCIENCE.COM!

As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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I’ve always been curious about this. Sometimes, after drinking a big glass of water, it seems like I pee it all out literally just a few minutes later. Is this just in my head, or is ingested fluid really processed that quickly? A new study by researchers at the University of Montreal, published online in the European Journal of Applied Physiology, takes a very detailed look at the kinetics of water absorption and offers some answers.

The study gave 36 volunteers 300 mL of ordinary bottled water, “labelled” with deuterium (an isotope of hydrogen than contains a proton and a neutron instead of just a proton) to allow the researchers to track how much of that specific gulp of water was found at different places in the body. They found that the water started showing up in the bloodstream within five minutes; half of the water was absorbed in 11-13 minutes; and it was completely absorbed in 75-120 minutes.

Here’s what the data looks like:

On the left, it shows how quickly the water was absorbed in the first hour, measured in the blood. On the right, it shows the gradual decay of deuterium levels over the subsequent 10 days, measured from urine samples. This, of course, shows that when I pee after drinking a glass of water, I’m not peeing out the same glass of water! Within ~10 minutes, fluid levels in my blood will have risen sufficiently to trigger processes that tell me to pee — but, according to this data, it takes about 50 days for complete turnover of all the water in your body.

The other wrinkle in this data is that the subjects showed two distinct absorption patterns (shown on the bottom and top), with about half in each group. In the top group, the water is very rapidly absorbed into the blood (possibly because these people get water out of the stomach and into the small intestine very quickly) before running into a slight bottleneck as the water is then distributed throughout the body to all the extremities. The second group, on the other hand, doesn’t hit this bottleneck: the flow of water out of the stomach and into the small intestine is slow enough that extra water doesn’t have a chance to build up in the blood before being distributed throughout the body.

So what does this all mean? I don’t have any particular practical applications in mind — I just thought it was kind of cool.

Extreme heat, dehydration and sodium balance

THANK YOU FOR VISITING SWEATSCIENCE.COM!

As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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Another interesting hydration study [UPDATED WITH LINK TO STUDY] from Tim Noakes and his collaborators, studying South African Special Forces soldiers marching in hot conditions — following up the one I blogged about last year. The basics: 18 soldiers did a competitive 25 km march (taking about four hours), carrying 26 kg packs and wearing full battle dress, in temperatures averaging 40.2 C and reaching a high of 44.3 C (112 F). They were allowed to drink only water. The main point: they did it, despite

environmental conditions that approached those considered to be unsafe for practice and competition by the American College of Sports Medicine. Furthermore, all soldiers completed the study successfully and none presented with either the signs or symptoms of ‘‘heat illness’’.

But it’s the details that are most interesting. They were allowed to drink as much as they wanted, and the amount they chose to drink led them to lose 3.8% of their body mass on average — too much, according to conventional thinking. But they showed no sign of trouble, and there was no link between the amount of weight each soldier lost and his finishing time. But (as their previous study showed), weight loss didn’t correspond exactly to water loss: for every 1 kg of mass lost, their total body water stores only declined by 200 g (for details of how this is possible, read the earlier blog entry).

More importantly, the sodium concentration in their blood didn’t change significantly (and neither did their overall plasma osmolality), even though weren’t taking in anything but water. They lost some salt to sweat, but they also lost some fluid, so the concentration stayed relatively constant.

At this sweat sodium concentration, average total sweat sodium losses during the march could have been >240 mmol. Yet despite such large losses that were not replaced during exercise, participants maintained their serum sodium concentration. This confirms the now well-established finding that serum sodium concentration can be maintained during exercise without the need for acute sodium replacement during exercise.

I’m sure plenty of people will disagree with that last sentence! Noakes’s argument is that, if you allow people to drink as much as they want and choose their own pace, they’ll automatically self-regulate in order to preserve homeostasis — and the crucial parameter that your body monitors is not weight or water content, it’s serum osmolality. So it’s no coincidence that the soldiers allowed themselves to get dehydrated to precisely the degree that matched the salt they lost in their sweat — that’s just the way the body works.

P.S. Random aside on dehydration: the introduction of this paper cites another study claiming that Haile Gebrselassie lost 10% of his body mass while setting the current marathon world record. Now that’s impressive!

Pre-drinking to hyperhydrate, and other heat-related research

THANK YOU FOR VISITING SWEATSCIENCE.COM!

As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

***

There’s a great (and timely) article called “Myths About Running in Heat” in the current issue of Running Times (linked to from Amby Burfoot’s latest blog entry), in which Phil Latter takes a look at six common myths relating to topics like thirst and acclimatization. It’s all good stuff, and worth a read.

The one that I hadn’t really thought about before was the idea of “hyperhydration” before running in the heat. In general, if you try to load up on fluid in the days or hours before a run, you’ll just pee it out. But Latter suggests two options. First:

Hyperhydrating, or drinking more fluid than is necessary to maintain fluid balance within the body, is effective right before an event because blood flow is severely reduced to the kidneys during exercise, thus limiting fluid excretion. “The trick then is to be able to absorb quickly and then tolerate the bloating feeling for a couple of minutes into the exercise period,” says [University of Sherbrooke exercise physiologist Eric] Goulet. “As the exercise progresses the intestine will slowly absorb the fluid, which will then be used for physiological regulation.”

Second is the idea of drinking “lightly salted water in the several hours preceding hot weather exercise” — a technique with a long anecdotal history that Goulet is currently testing in the lab:

The biggest trick, Goulet concedes, is making the substance palatable. For his trials, Goulet had the salt water ( just over ¼ teaspoon of table salt per cup) blended with Crystal Light and served at roughly 35 degrees, but adds, “You have to find what works best for you.”

One other interesting point is the idea that drinking fluids helps you deal with heat better — a claim that most people (including exercise physiologists) accept absolutely uncritically. Not everyone agrees, though:

After performing a thorough meta-analysis, Loyola University’s Jonathan Dugas, a well-known blogger on the Science of Sport website, explains why. “I’m not saying there’s no effect of fluid on body temperature, but you have to really qualify it,” he says. “The effect is really small. Maybe a half degree in temperature, maybe less.” […]

His research suggests hydration levels have almost no effect on one’s likelihood of suffering from even the most extreme of all heat-related issues, heat stroke. […]

“On a very hot day,” Dugas says, “no amount of drinking is going to change the fact that you’re going to go slower. You can drink up to 100 percent of your body mass, and it won’t keep you from running slower.

For practical purposes, of course, this doesn’t mean that water isn’t a special concern on hot days. The heat will make you sweat more, so you’ll need to drink more that match thirst. But it challenges the widespread assumption that when someone at a race collapses from heat stroke, one of the causes was that they didn’t drink enough water:

Current research suggests that some combination of genetic predisposition, infection, muscle damage, sleep deprivation and high levels of exertion may lead to heat stroke… water intake (or the lack thereof) isn’t mentioned.