Author: alex

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Drinking only to thirst (no more, no less) improves performance

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My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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It’s official: drinking to perfectly maintain fluid levels makes you slower, not faster. At least that’s the message in a new British Journal of Sports Medicine meta-analysis, from Eric Goulet at the University of Sherbrooke. What’s new here is the recognition that there’s a fundamental difference between treadmill or bike tests where you continue at a set pace until exhaustion, and “real world” time trials or races where you cover a given distance as fast as possible. Many of the classic studies underlying the orthodox view (that losing more than about 2% of your body mass hurts endurance performance) are time-to-exhaustion tests:

These tests with no known end points are unrepresentative of out-of-door exercise conditions faced by field athletes and therefore possess a very low ecological validity [Goulet writes], which therefore question their value and relevance in the design of fluid intake guidelines aimed at maximising endurance athlete performances.

To address this point, Goulet reviewed five studies that looked at dehydration in self-paced cycling time trials — and his conclusions were starkly different from the conventional wisdom. On average, subjects in these studies with an average dehydration of 2.2% of body mass actually had a non-significant improvement in performance of 0.06% compared to subjects who drank enough to roughly maintain body mass (losing an average of 0.44% body mass).

Drinking according to the dictate of thirst was associated with an increase in [time trial] performance compared with a rate of drinking below (+5.2±4.6%, p=0.01) or above (+2.4±5.0%, p=0.40) thirst.

Is this shocking? Well, it agrees with what Tim Noakes has been arguing for several years. It also agrees with real-world data like this study from a marathon in France, which found that sub-3:00 finishers lost 3.1% of their body weight, 3:00-4:00 finishers lost 2.5%, and slower-than-4:00 finishers lost only 1.8%. Will it change anyone’s mind? Goulet is hopeful: he says the findings should “contradict and abolish the old and much-believed dogma stating that ‘during prolonged exercise it is of capital importance to drink ahead of thirst, otherwise it is already too late.'” I’d like to think that’s true, but I suspect it will take quite a few new studies before opinions start to shift.

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Palm cooling for endurance sports

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My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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A reader sent me a link to Bex Runner’s “core cooling device” — essentially a small gel pack that you freeze and strap to your palms. So is it a useful device, or a stupid gimmick? Tough call.

There has actually been a fair amount of research on palm cooling over the last decade or so. I blogged last year about a study that found people lifting weights were able to lift more if they cooled their palms between sets. In that case, the palm-cooling device was a fancy one that also applied negative pressure to the palm to help prevent blood vessels from constricting with the cold. That ensures that lots of blood flows through the open vessels, past the cool palms, in order to better cool the rest of the body.

Still, the total cooling power of these devices is rather limited. Another study published last year compared the same palm cooling device to an Army cooling vest, and found that the palm cooling didn’t reduce heat strain during treadmill walking. They estimate that the vest was able to extract 55% of the heat generated during the trial, while palm cooling was only able to extract 14% of the heat.

The palm-cooling stuff is just one, small branch of the “ergogenic cooling” literature, and all sorts of theories have been proposed about how it does or doesn’t work. The crucial message that the weight-lifting study tells us, is that it doesn’t work by altering local muscle physiology. The chest muscles weren’t cooled, and yet the weight lifters lifted more weight. As the authors (from Robert Robergs’s group at the University of New Mexico) wrote:

[O]ur findings can only be explained by the central processing of peripheral input from afferent nerves and/or changes in core blood temperature and as such these results fit within the theory of the [Central Governor Model] of the regulation of fatigue and the final cognitive decision to end exercise.

If that’s the case, the palm-cooler doesn’t need to actually alter your physiology to make you run faster — it just needs to convince your brain that your body is in less distress than it would otherwise be. Does this particular Bex device do that in way that makes a practical difference to running performance in the heat? I have no idea — they need some independent studies to demonstrate it. But the mechanism is plausible.

(If it does work, there are still some questions. At a race, you’d have some logistical difficulties keeping it frozen until the start. For training, we get back to the question: is it really useful to use devices that make training easier? Or is that sort of self-defeating, because the whole point of training is to challenge yourself? If you run a tempo run in 30 minutes unaided, or 29 minutes with cooled palms at the same effort, do you actually get any superior benefit from the faster pace at the same effort? Or do you lose an opportunity to adapt to heat?

Training aside, I suppose if it enhances comfort on a hot day so that you can simply get your run in, that’s a plus.)

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Science of Marathon Training night in Toronto: June 6!

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My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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Very exciting news: the Scotiabank Toronto Waterfront Marathon is having its official launch night on Monday, June 6, which will feature a lecture by yours truly on the “Science of Marathon Training,” followed by an “Ask the Experts” panel discussion with Q&As with some very exciting running stars (names to be announced soon). All the details are available at this page on the STWM site — including a form to register. The event is free, but seating is limited to 200 people, so please sign up as soon as possible to reserve a spot. [UPDATE: The event is sold out as of May 24.]

The event will be held at the Marriott Downtown Eaton Centre, in the Trinity Ballroom, from 6:30 to 9:30 p.m. (there will be an expo, and the talks will start at 7:15 p.m.). It’s going to be a great night: draw prizes, fantastic panellists, and of course an opportunity to pick up signed copies of Cardio or Weights. 🙂 Hope to see you there!

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Overcoming confirmation bias

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My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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We often wrangle over the nature of scientific evidence here at Sweat Science, so Jonah Lehrer’s recent blog post on the “argumentative theory” should be of interest to many readers. It’s a new explanation for why humans are so prone to confirmation bias — our habit of seeking out evidence that confirms our expectations and ignoring evidence that contradicts them:

In essence, [researchers Hugo Mercier and Dan Sperber] argue that human reason has nothing to do with finding the truth, or locating the best alternative. Instead, it’s all about being able to argue with others.

Here’s how Mercier explains the theory:

[T]he problem with the confirmation bias is that it leads people to make very bad decisions and to arrive at crazy beliefs. And it’s weird, when you think of it, that humans should be endowed with a confirmation bias. If the goal of reasoning were to help us arrive at better beliefs and make better decisions, then there should be no bias. The confirmation bias should really not exist at all.But if you take the point of view of the argumentative theory, having a confirmation bias makes complete sense. When you’re trying to convince someone, you don’t want to find arguments for the other side, you want to find arguments for your side. And that’s what the confirmation bias helps you do.

The idea here is that the confirmation bias is not a flaw of reasoning, it’s actually a feature. It is something that is built into reasoning; not because reasoning is flawed or because people are stupid, but because actually people are very good at reasoning — but they’re very good at reasoning for arguing.

Lehrer concludes that the theory “paints a rather bleak portrait of human nature.” Certainly, we all see confirmation bias in others but struggle to recognize it in ourselves. The idea that this is how we’re wired can lead to a somewhat nihilistic view of the chances of figuring out “the truth.” But in the comments section, Mercier offers a different perspective:

[W]e’re not being quite as pessimistic as that. Even if the function of reasoning is not to pursue the truth directly, we suggest that reasoning can still lead us to better beliefs and decisions. The trick is to rely more on reasoning in group and, more specifically, on the evaluation of arguments as opposed to their production. The production of arguments is biased–as you describe. But argument evaluation ought to be fairly objective: after all, in many cases you’re better off being convinced rather than clinging to false beliefs… When people are in groups and argue about logical, mathematical or factual problems, they robustly converge on the best solution.

It almost sounds like he’s talking about Sweat Science! 🙂 So thanks to all who chime in with comments and critiques, as we all struggle to tear down each others’ confirmation biases.

[Thanks to Brian for pointing out the article.]

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The priming effect: how a hard warm-up can help performance

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My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

***

Most people who do hard interval sessions will have noticed this mystery: why does the second or third interval usually feel easier than the first one? I always figured it had to do with “getting into the rhythm” or something along those lines. Whatever the reason, Pete Sherry — my main training partner for 2002-2004 — and I eventually decided that we’d run 2x400m in ~72 sec a few minutes before every workout, in the hopes of making the first interval feel easier. Our impression was that it worked, and we started doing it before races too.

It turns out there’s plenty of physiology behind this. If you suddenly start running at a hard pace, with no warm-up, it takes a while before your body can adjust to start delivering oxygen to your muscles at its maximum possible rate. That’s one of the reasons VO2max tests take 10-12 minutes, rather than simply involving a short, all-out sprint. It takes time for the blood flow to your muscles to increase, and for the enzymes that extract oxygen from the blood and oxidize fuel to ramp up their activity levels. A good warm-up gets this ramp-up process over with, allowing your body up to deliver more oxygen to muscles right from the start of the workout or race, and reducing the temporary oxygen debt.

Still, most people warm up with gentle jogging, flexibility drills, and some short sprints. But how about including a six-minute “hard” effort (above lactate threshold but below VO2max pace), about ten minutes before the start of your race or workout? Would that “prime” your oxygen kinetics even more? The challenge is as follows: a sustained burst of hard exercise (above threshold) definitely improves how quickly your body can process oxygen once the actual race starts; this effect can last for a half-hour or more. If you exercise too hard, on the other hand, you deplete your anaerobic energy stores (phosphocreatine), and metabolites build up in your muscles that may slow you down. Numerous experiments over the past decade have found conflicting results: depending on the precise details of the duration, intensity and recovery time following the “priming” burst, performance either increases, decreases, or stays the same.

A new cycling study just posted online at Medicine & Science in Sports & Exercise, from Mark Burnley’s group at Aberystwyth, adds some more data on finding the right balance. They used a six-minute priming bout, 10 minutes before the “race” — a formula that other studies have found to be effective. For intensity, they compared “heavy” (about 25% of the way between threshold and VO2max power) and “severe” (about 63%) priming bouts. The findings: “heavy” priming boosted oxygen kinetics and significantly increased time-to-exhaustion in tests ranging from ~2-10 minutes. “Severe” priming also boosted oxygen kinetics, but didn’t increase time-to-exhaustion, suggesting that the downside of depleted anaerobic reserves outweighed the benefits of more aerobic energy available early in the test.

So what does this mean in practical terms? It’s hard to know how generalizable this protocol is, but I’d say it’s worth experimenting with some sort of extended surge ~10 minutes before the end of your warm-up. If you’re doing a six-minute effort, it looks like you should aim just above your threshold. I know quite a few runners who have incorporated similar but shorter surges of ~1-2 minutes into their warm-up routine. There may be a good argument for runners to stick to shorter surges, since the impact of leg-pounding is a bigger factor than it is in cycling. In that case, you may be able to get away with a higher intensity. But so far I don’t think the research has answered that question — for now, it’s trial and error.