I’m writing a book with my colleague Adam Hammond, with the working title This Is Your Brain on Running. It’s an attempt to understand what running does to our brains, how that makes us feel, and why we keep coming back for more. One thing we’ve figured out for sure is that there’s no single answer to this question. Everyone has a different version of what Alan Sillitoe (in The Loneliness of the Long-Distance Runner) called the “barmy runner-brain.” Others have described an “altered state of consciousness,” an enhanced version of themselves, that takes over when they’re running.

We’d love to hear about your experience of running through the questionnaire at this link. There are no right or wrong answers here, so please dive in!

Thanks for sharing your stories!

Alex Hutchinson and Adam Hammond

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Ease off the ups, push the downs

There’s a study from back in 2010 that has really stuck with me. It used a portable VO2 analyzer on runners running a hilly 10K course, to figure out when they were pushing harder than average and when they were going easier. The results: they consumed more oxygen (and thus energy) on the uphills, and less on the downhills. Seems obvious, right?

But in a perfect world, that’s not how you would pace yourself. You would slow down enough on the uphills to keep your VO2 roughly constant, and speed up enough on the downhills to do the same. Instead, our “constant speed” bias overrules our desire for constant effort.

My leg at Cabot was 20K long with a big climb ascending around 300 metres over the course of 3 or 4 kilometres, then descending the same amount over a slightly longer distance. Before the race, I reminded myself of the easy-up, hard-down plan. And I’m happy to say that I executed it pretty well. I’m generally a strong climber, so my mantra on the way up was “Don’t pass that guy in front of me! Don’t pass him!” This required dialing back, so I reached the top feeling good, and was able to attack the long descent. That went pretty well too… until the final mile, when the pounding finally became too much for my legs and I lost about a minute on the runners around me. All in all, though, I think I got the most out of myself with this approach.

Cushion the blow

I’m not a supershoe denier (far from it!). They definitely work. But even though I’ve written a lot about them, I mostly haven’t run in them other than a review pair of the OG Vaporfly that I got from Runner’s World back in 2017. Most of my running goals these days are internally driven, so I’m not all that interested in getting a few percent faster with no effort.

Two things were different about this race. One is that I was part of a relay team with competitive aspirations in the masters division, so saying “I don’t really care about times” would be pretty selfish of me. The other is that I was initially slated to run two legs of the relay. I eventually weaselled out of this fate, but at first I was very concerned about the challenge of running back-to-back hilly ten-milers with only a half-day of rest in between. As a relatively low-mileage runner, I figured I needed all the recovery aid I could get, and there is indeed some preliminary (albeit Nike-funded) research suggesting that cushioned supershoes reduce muscle damage—so I ordered some billowy new kicks.

In the end, I only ran one leg—but it did have that punishing half-hour continuous descent from Cape Smokey. I’ve had some crippling muscle soreness after mountain races with long descents. This time I felt surprisingly good in the aftermath. Not great. A full week later, when I tried to run for an hour, my quads gave out after 45 minutes. But overall I think it was worth the money.

Social energetics

The team I was running with is affiliated with the Toronto Harriers, a group in my home city. I knew a few of the guys beforehand, and had seen most of their names in local race results over the years, but they were mostly new to me. By the end of the weekend—including something like 28 hours hopping in and out of vans—they were like brothers to me. That’s how these things go. And it’s actually a big part of the reason we do it, I think.

I’ve got an article in the upcoming Summer print issue of Outside on a concept that has recently been dubbed “social energetics,” which describes the changes in how we allocate energy in presence of others. One of the scientists I spoke to was Emma Cohen, an evolutionary anthropologist formerly at Oxford University. My first encounter with her research was a 2009 study in which she showed that Oxford rowers had increased pain tolerance after a workout—but that the increase was twice as big when they worked out with their teammates compared to when they did it alone.

Running is often thought of as a solitary sport, as are other endurance sports. And it can be. But it can also be a medium of incredible bonding. I’ve always loved relay races, team-scored cross-country, and other contests where social energetics are at the fore. I’m pretty confident that I dug way deeper on the Cabot Trail than I could have in any standard solo race. (That said, my Harriers team was roundly defeated—you might even say sucker-punched—by a super impressive masters team from Cape Breton Road Runners. Chapeau, guys!)

Other stuff

For Outside, I wrote about a study claiming that warming up your brain with three-minute cognitive tasks on a smartphone can improve mile run time by a couple percent. I’m cautious about what those results really mean, but I think they might be telling us something important about what a warmup is really for.

I also wrote about a study suggesting that women have better “fatigue resistance” than men—that is, that traits like VO2max and running economy change less with fatigue. I figured the study was timely given the excitement around Rachel Entrekin’s recent overall triumph at the Cocodona 250. I’m not convinced Entrekin’s main edge is physiological, but it’s food for thought.

Quick service note: the Outside articles above are behind a paywall. The exact nature of that paywall changes as they explore different models; sometimes there are free articles available to non-subscribers, other times there aren’t. I genuinely wish all articles could be available for free, but Outside—like many publications these days—is trying its best to find a way to be financially viable. For what it’s worth, I think $60 a year for full access to Outside and its ten sister publications (including RUN, Backpacker, Velo, and more) is a great deal! I write four Sweat Science columns every month for them, and that regular gig has been the anchor of my writing career.

Finally, I had a lot of fun writing this essay for Big Think about why play brings us pleasure. It frames play in the context of brain science’s big new “theory of everything,” predictive processing, and ponders the “Dark Room” problem: if our brains seek to predict the world with maximum accuracy, why don’t we just lock ourselves in the closet instead of venturing out to play in the unpredictable world? The essay draws on ideas I dug into in my recent book, The Explorer’s Gene (which, of course, I hope you’ll check out—especially since it’s currently 51 percent off on Amazon.com!).

Many thanks for reading,

Alex Hutchinson

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Aerobic vs. Anaerobic

Here’s a fun graph from a recent review in Sports Medicine looking at the balance between aerobic and anaerobic energy contributions in exercise, by Paul Gastin and Haresh Suppiah of La Trobe University in Australia. This is for 90 seconds of all-out cycling:

What are we seeing here? There are actually three distinct energy systems that fuel our muscles during exercise:

(1) Phosphocreatine (labelled here as ATP-PCr) uses fuel stored right in the muscle and kicks in immediately, but only lasts for about ten seconds. It’s anaerobic, meaning that it doesn’t require oxygen, but makes an essentially negligible contribution to extended efforts.

(2) The glycolytic pathway is the one we usually think of as the “anaerobic” system, and is one that produces lactate as a byproduct. In this short sprint, it peaks after about 20 seconds and then declines sharply.

(3) “Oxidative phosphorylation” is what we think of as aerobic energy. It takes a while to ramp up, but for efforts lasting longer than a few minutes it’s by far the dominant source of energy. That’s why, say, good 5K runners tend to be good half-marathoners even though the distances are very different: the fuel source is the same.

What’s interesting in the graph is the crossover point, where aerobic energy surpasses anaerobic energy. In this case, that looks to happen after around 40 seconds; for the rest of this 90-second effort, the cyclist is relying mostly on aerobic energy.

You can also ask a slightly different question: for what length of race is the total contribution of anaerobic and aerobic energy 50-50? The model in the paper suggests that occurs for a race lasting around 75 to 80 seconds. That’s very different from what scientists (and curious runners) thought back in the 1990s, when the assumption was that the mile, lasting around four minutes, marked the 50-50 crossover from anaerobic to aerobic. More recent research has suggested that the crossover is closer to 800 metres (around two minutes); this pushes it even lower.

The takeaway? Aerobic fitness is crucial, even for shorter events. That, in a nutshell, is why runners and cyclists and swimmers and other endurance athletes do so much mileage, even if their event only lasts a few minutes.

Other Stuff

For Outside subscribers, I’ve written about a couple of other recent studies. One is a comparison between age-related decline in leg muscles and jaw muscles. The thinking is that, even if lifestyle changes nudge us to become less active as we get older, we’ll keep chewing our food vigorously. So the weakening and/or atrophy of jaw muscles should offer a true measure of pure aging, unaffected by changes in exercise habits. Sure enough, the data suggests that we lose leg muscle at roughly twice the rate we lose jaw muscle.

The other article revisits a common claim that women are “better” at pacing marathons than men. There are a bunch of studies with real-world data that seem to support this claim, with men being far more likely to slow dramatically in the late stages of the race. It’s often presented as evidence that evolution has wired men to have a greater tolerance for risk than women. But a rigorous reanalysis by a pair of statistics experts argues that the disparity has been overstated, and any remaining differences could easily be explained by social factors.

Last thing: Amazon U.S. currently has my new book, The Explorer’s Gene, on for 46 percent off. If you enjoy this newsletter, the best thing you can do to support it is pick up a copy or three of the book.

Thanks for reading!

Alex Hutchinson

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First, some quick housekeeping. You might have heard some vague rumours about a fast marathon in London last week. I shared some thoughts about sub-two and how we got there in an article for The Atlantic (gift link here). I also had fun conversations about it with the folks at Marathon Handbook and with the sports psychologist Stuart Holliday.

For Outside subscribers, a couple of new articles: one reviewing the evidence (or lack thereof) behind ten of the most popular peptides being hyped for athletic performance; and another on how the explore-exploit dilemma applies to sports in contexts like choosing a sport, switching to a new training plan, or making in-competition tactical decisions. I spent a lot of time digging into the explore-exploit dilemma while writing The Explorer’s Gene, so it’s fun to see sports science researchers starting to think about it.

The Joy of Less Freedom

Okay, onto the main event. David Epstein is one of the best science writers working today, and also one of the best storytellers. His first book, The Sports Gene, is my pick for the best sports science book of all time. His new one, Inside the Box, is about how limits stimulate creativity and more. Here’s our Q&A:

AH: Channeling our mutual friend Michael Joyner, could you start by giving us the key message of your book in the form of a haiku?

DE:

More more more more more

Makes us less creative and —

Less satisfied too.

AH: Bravo. :) What got you interested in this topic?

DE: Two main things. First was the most common question I received from readers after my last book, Range. That book was about the benefits of breadth in a specialized world, and the question was along the lines of: “Ok, I’ve got these broad skills and experiences, now what?” Good question. At some point, it has to be focused into achievement, and, hopefully, meaning and satisfaction. So this book felt like a natural progression from the last one.

Second: a hefty dose of “mesearch.” I have been simply terrible at drawing useful boundaries around my own projects. Why do I finish a book once every six years? Partly because I wasn’t thoughtful about putting useful constraints in place. For my first two books, I wrote 150% of a book in order to get a book. I didn’t define the project well, so I had a ton of bloat, went way over length, and then had to cut back. I cut a trip to Arctic Sweden from my first book! This time around, before I wrote a single word, I made a detailed structural outline—an architectural plan, basically—on one single page. And if it isn’t on that page, it isn’t in the book. The book ended up 20% shorter than the previous two and, I think, more coherent. The writing is tighter, and I’m not burned out.

Lastly, I also just constantly felt overwhelmed with decisions and information overload, and I wanted to see what research had to say about potential antidotes to that.

AH: I can identify with that! Still, this is a book where I started out thinking “Boy, this is a tough claim to make, and he’s going to have trouble convincing me that his thesis applies outside certain narrow niches,” and finished thinking “This is so completely and overwhelmingly obvious that I can’t believe anyone, including me from last week, ever thought differently.” Are the experts all in agreement here, or are there still people arguing that, say, unconstrained free brainstorming is the best way to come up with fresh ideas?

DE: It’s interesting you say that. With Range, when I told people I was writing about the power of generalists, I usually got a raised eyebrow. With Inside the Box, when I said I was writing about how constraints can be your most powerful tools for creativity, productivity, and satisfaction, the response was usually much more positive. “Oh, that’s totally true!” But then people often had trouble articulating why they felt that way. So I think maybe Inside the Box gets at something that many of us feel intuitively, but aren’t sure why. I hope I can help us articulate the why and how.

As far as the research on creativity, there is pretty overwhelming agreement that constraints are helpful and often actually required for innovation. With too much freedom, our brains will just go down what some cognitive psychologists call the “path of least resistance”—doing the usual thing—so we actually need that to be blocked in order to have new ideas. There are nuances in the research, of course. There’s a mountain of research showing that constraints spur creative problem solving—unless you basically prescribe what someone has to do and how they have to do it, in which case creativity plummets. If you’re dealing with a constraint, or thinking about imposing one, ask: “Does this leave room for me to surprise myself?” If the answer is no, it’s gone too far. There are also nuances with constraints like deadlines. They can either boost or impair creativity, depending on whether they lead people to monotask (good) or multitask (bad). As Duke Ellington said: “I don’t need time. What I need is a deadline!” Deadlines got him to monotask, which he never did otherwise.

In terms of group brainstorming specifically, it’s pretty unequivocal: it doesn’t work. In an international survey by psychologists of known creativity myths, the second most popular was “one is most creative when with total freedom in one’s actions.” The first was that group brainstorming is best for idea generation. Try “brainwriting” instead. Everyone writes down ideas separately, and only then do you come together as a group to discuss.

AH: You’ve been making awesome videos lately on Instagram and YouTube—a medium that has great power but also, compared to writing, a lot of constraints on how you can convey complex ideas. Have you learned anything from grappling with these constraints?

DE: Have I ever! The short videos are about one minute long. That is crazy short for a digressive person like me. It has a tremendous clarifying effect in terms of forcing me to think about the main point I want to share. Or, if I’m storytelling, how to give a sense of story as concisely as possible. And that’s one thing that useful constraints do: they force you to clarify priorities. That’s actually the main mindset shift I hope the book engenders—from seeing obstacles only as stifling to viewing them as opportunities to clarify priorities and launch into productive exploration.

One of my weaknesses as a public communicator has been helping people think of practical applications of my own work. Short-form videos are definitely getting me to think more in that way. And I need training in that regard, so I’m valuing that tremendously. I’ve also learned that I actually like making short videos. It’s been the opposite of what I expected. I thought I’d like making the long YouTube videos and dislike the short Instagram videos. But, so far, it’s the opposite. The learning rate, and ability to experiment quickly with the short videos is engaging, and it’s so new to me that it feels challenging and fresh. It’s a bit of a merger of Range and Inside the Box for me—doing something new and uncomfortable in a very confined space.

AH: Do endurance athletes have anything to gain by imposing or accepting constraints on themselves?

DE: Yes, in several different ways. There are the obvious things, like capping intensity so you can increase training volume. Or putting a limit on pace on recovery days (harder than it sounds). A lot of endurance athletes are kind of in love with constraints, whether they know it or not. The legendary track coach Jumbo Elliott famously told his athletes to “live like a clock.” Hyperstructure, habit, ritual, saying “no” to almost everything. The constraints have an incredible clarifying effect on your life, and help give it meaning. To me, that structure is arguably the greatest thing about being an endurance athlete. I missed it sorely when I stopped competing.

I can think of some silly ones too. I’ve always been a night owl. But beginning about two years ago, I wanted to start working out early in the morning. So I started going to sleep in running clothes or workout clothes. I wake up and it’s like: “Am I really going to change out of this now? No, I am not. Let’s get after it.” It’s silly. It’s a little embarrassing. It absolutely worked. I’m working out every morning now, like clockwork, and I was never working out in the morning before.

There’s also a less obvious tip for endurance athletes. I have one chapter in the book on what’s called the “theory of constraints.” This is an idea that came from a physicist studying industrial production, and the core concept is that all systems are limited by their single slowest or least efficient step. Every machine in the factory can be humming except one, and the overall system will run at the speed of the slowest machine—the “bottleneck.” In the book, I tell the story of a swimmer who missed the US Olympic Team—by a lot—and retired. But then, in one of her last college classes, she learns about the theory of constraints and decides to un-retire and apply it to her training. She identifies and works on her limiting factor, which was her power. She had a massive aerobic engine, but she was only 5’2”, and her coaches had her working on the thing she was already good at, not the thing that was limiting her. Long story short, she applies the theory of constraints to her training and wins an Olympic gold medal. In the end, she goes on to become the only woman ever to compete in three different sports across four Summer Olympics!

The story really resonated with me, because I had a similar experience as a walk-on 800-meter runner in college. I didn’t know the language of the theory of constraints at that time, but at a certain point I realized that recovery was my bottleneck. I simply did not recover at the rate of my peers, and yet I was doing the same volume and intensity. I eventually scheduled a class over one workout a week to have an excuse to take it easy. It was a massive boost to my performance, and my sense of wellbeing, honestly. I ended up twice All-East, and was given this university award for “the athlete who achieved significant athletic success in the face of unusual challenge and difficulty.” Pretty funny. My unusual challenge and difficulty just being that I was really, really bad at first, and then I got good. So it’s not that the constraint itself is good in a case like this, but it shows you where to focus, and that’s incredibly powerful.

***

Big thanks to David for sharing his thoughts. The new book comes out on Tuesday (links to order here)—and if you pre-order before then, you’ll receive bonus Q&As with the novelist Isabel Allende, Tony Fadell (the guy who created the iPod), Ryan Poles (the Chicago Bears GM), and the chef David Chang about the role of constraints in their lives. Details on the bonus offer here. Honestly, the David Chang Q&A is worth the price of the book on its own—hilarious and absolutely fascinating.

Thanks for reading! If you enjoyed this and would like more author Q&As in future newsletters, let me know in the comments below.

Alex Hutchinson

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Iñigo Mujika of the University of the Basque Country, along with colleagues in Canada and Australia, has an interesting new paper in the International Journal of Sports Physiology and Performance. It asks whether barometric pressure affects how athletes respond to altitude training camps, using data from 27 elite swimmers and water polo players across 11 different training camps at the Sierra Nevada High Performance Center in Spain, which is at 2,320 metres (7,600 feet).

The motivation for the study is the famously inconsistent effects of altitude training (which I’ve written about previously). Everyone agrees that the theory of altitude training—less oxygen in the air spurs your body to produce more red blood cells—is great. But in practice, it’s very hard to predict who will benefit from a given stint at altitude and by how much.

Perhaps, Mujika and his colleagues surmise, that’s partly because the oxygen levels in the air fluctuate depending on barometric pressure. Indeed, in the data they collected, the “equivalent altitude” varied by as much as 130 metres (427 feet) within a given day and 296 metres (971 feet) over the course of a week thanks to barometric pressure changes. The athletes used a finger oximeter to test the oxygen saturation of their blood every morning. Sure enough, a higher barometric pressure corresponded to higher oxygen saturation. That could be enough to alter the training stimulus, and perhaps even to push some of the athletes into under- or overtraining.

That’s the headline result, but there’s a lot more detail buried in the paper. The scientists also monitored a bunch of other weather parameters: humidity, solar radiation, wind, precipitation, and so on. They looked for correlations between these weather conditions and various markers of fitness and fatigue, both immediately and for up to 24 hours afterwards. Several patterns popped out: for example, athletes slept better after a day with lots of sun, and slept poorly in precipitation and wind.

More subtly, they also reported higher levels of fatigue when solar radiation over the previous 8 to 12 hours was high. That fits with previous research showing that, even if temperature and humidity are held constant, running in full sunlight can cut your time to exhaustion in half compared to an overcast day. Mujika’s study suggests that there are more patterns like this waiting to be uncovered, and I suspect they’re not just relevant at altitude training camps. Conditions matter—which might explain why I check my weather app so obsessively.

Other Stuff I’ve Written About Recently

For Outside:

• Researchers spot-checked 600 day-hikers and trail runners at Rocky Mountain National Park to find out which of 13 essential backcountry preparedness items they had with them and check other aspects of their prep. The bottom line: most were not adequately prepared to venture into the mountains.

• “One-rep max” seems like the obvious way to prescribe weight training and track progress. But some researchers now argue that it’s inaccurate, risky, and unnecessary, and we’re better off with subjective effort or using apps that track bar speed.

• There has been lots of attention paid to the risks of losing muscle on GLP-1 drugs like Ozempic. But what about aerobic fitness, and functional tasks like stairclimbing? A new analysis finds that, as you might guess, losing weight alone doesn’t help: you need to exercise.

For the Globe and Mail:

• Strength training helps reduce pain and rehab injuries by making you stronger… right? That’s the obvious assumption, but the evidence for that claim is weak. According to one analysis, increased strength explained only two percent of the benefits of strength training in people with osteoarthritis. Instead, the mechanisms may be more subtle, for example reduced inflammation or less fear of movement.

That’s all for now. Thanks for reading!

Alex Hutchinson

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A new paper in the International Journal of Sports Physiology and Performance makes the case that pacing lights really are helping runners go faster. A team led by Pablo Comino of Spain’s Rey Juan Carlos University analyzed 45 Diamond League 1,500-metre races between 2021 and 2024, of which 33 featured pacing lights and 12 didn’t. The overall conclusion is that the Wavelight races were faster (by about four seconds, for those in the top half of the field)—and, crucially, paced more evenly, with fewer position changes.

Here’s one of the key graphs, showing average pace for runners finishing in the top four of each race:

The key moment comes at the end of the first lap, after the initial jostling for position has settled down. This is where the runners tend to settle into a slower, more sustainable pace. But the pacing lights remind them not to settle too much, spurring them to maintain a slightly quicker tempo. In the final lap of the race, the unpaced runners are able to speed up more, but not enough to make up the time they lost in the middle section of the race.

There’s another interesting visual, showing the average intermediate placings of each of the top 12 finishers for both types of race. Check out how much passing and disruption there is in the non-Wavelight races, while in the Wavelight races the runners mostly seem to tuck in along the rail and stay in one position:

There are some important limitations to this analysis. Most notably, it may be that athletes were more likely to chase fast times in Wavelight races, and to focus on placing on non-Wavelight races. Comino’s paper includes a list of no less than 26 world records set with pacing lights between August 2020 and May 2025. That’s hugely impressive, but it’s hard to imagine that any of those runners would even have attempted a record at a meet with no Wavelight.

Still, the links between pacing lights, more even pacing, fewer position changes, and faster times is pretty compelling—and the message is relevant even to those of us who may never encounter pacing lights. To me, the benefits of tucking behind another runner have always seemed bigger than drafting alone: pacing yourself correctly requires a lot of mental effort, and I’d rather save that effort for the latter stages of the race.

Was that TLDR?

You can also check out my two-minute video summary of that Wavelight study. I’ve been playing around lately with super-short videos on Instagram about key studies or insights. Some of the other topics I’ve discussed are what to think about when you run, running cadence, and the difference between how hot you feel and how hot you really are. Let me know what you think in the comments!

Meanwhile at Outside…

My latest Sweat Science columns tackle:

• the six dimensions of “coachability” and why they matter for your performance even if you don’t have a coach;

• why 7 out of 10 might be the effort sweet spot (in at least some contexts) for interval workouts;

• how sitting less can improve mitochondrial health and metabolic flexibility;

• the potential benefits of baking soda for enhancing performance at altitude.

On the podcast circuit, I had a super interesting conversation with Eric Zimmer on The One You Feed about personal exploration (drawing on my recent book The Explorer’s Gene, which I hope you’ll check out!), and earlier this year I chatted with Ross Tucker and Mike Finch about the challenges of science/health/sports journalism on The Real Science of Sport Podcast.

Thanks for reading!

Alex Hutchinson

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The study that prompted my article was a new review in Current Biology by Herman Pontzer and Eric Trexler of Duke University, aggregating and reanalyzing the results of a bunch of previous studies. The most attention-grabbing claim in the abstract is the following: “In human aerobic exercise interventions, total daily energy expenditure increased by only ∼30% of the change expected from additive models.” In other words, if you start an aerobic exercise program that burns 100 calories per day, you should expect that your total daily calorie burn will only increase by 30 calories.

It’s a big claim, and it got picked up in press coverage by, e.g., New Scientist. But I don’t think it’s right. The number is based on data from 18 previous study cohorts with a total of 368 subjects, all of whom had their daily calorie burn measured using a technique called doubly labelled water before and after starting an exercise program. Here’s what the data from those studies (plotted from the supplementary data table published with Pontzer and Trexler’s new paper) looks like:

Each of the circles represents the average result from a previous study, with the size of the circle proportional to the number of subjects in the study. On the horizontal axis is the expected increase in daily calorie burn, based primarily on how many calories their exercise routine burns. On the vertical axis is the actual measured increase in calorie burn.

In the simple traditional view, your daily calorie burn should increase by 100 percent of the calories burned during exercise. If that were the case, you’d expect the data points to fall along the orange dashed line. In reality, we suspect that some compensation occurs: if you start exercising more, you might be less active during the rest of the day, for example, so your overall calorie burn won’t increase by as much as expected. If that’s true, the data points will mostly fall below the orange line.

Pontzer and Trexler’s claim is that we only burn about 30 percent as many calories as you’d expect, which is shown by the blue dashed line. But that line doesn’t seem to fit the data. A weighted fit of the data points (constrained to go through the origin for simplicity) suggests that we actually burn about 59 percent of the expected calories, shown by the red dashed line. That’s still an interesting finding, but it’s off by a factor of two compared to the number reported in the abstract.

So what happened here? At first I assumed it was simply an arithmetic error, but it turns out to be something more subtle. To come up with their number, Pontzer and Trexler calculate a quantity they call “percent compensation” for each study, then take a weighted average of those values. If you burn 100 calories exercising but your daily calorie burn increases by only 30 calories, your percent compensation is 70 percent. The formula for percent compensation is:

(expected calorie increase – observed calorie increase) / (expected calorie increase)

That’s all fine and makes sense—except that there’s a problem if the expected calorie increase is zero. Then your percent compensation is infinity, no matter how many calories you actually burn, because you can’t divide by zero. Even if the expected calorie change is close to zero, you’ve got a problem.

Imagine you begin an extremely light exercise routine that burns 1 calorie. Doubly labeled water is supposed to be accurate to within a few percent, which for daily expenditure of 2,000 calories should be within, say, 50 calories in each direction—so even with no actual compensation, you might measure an increase of 51 calories or a decrease of 49 calories after you start exercising. That corresponds to percent compensation of either negative 500 percent or positive 500 percent, respectively, simply due to random measurement fluctuations. This is clearly nonsense, and doesn’t reflect any true “compensation” to the 1-calorie-per-day exercise routine.

None of this would matter under normal circumstances, because no one is interested in exercise programs that burn zero calories. But losing weight also changes your expected calorie burn. One of the studies in Pontzer and Trexler’s analysis—the largest one, as it happens, indicated by the yellow circle in the graph above—involved subjects who lost roughly 25 pounds by dieting in addition to exercising. They burned 100 calories per day exercising, but the diet-related weight loss decreased their expected calorie burn by 117 calories per day, meaning the overall expected change was negative 17 calories—very close to zero, where the percent compensation calculation breaks down.

Sure enough, the percent compensation in this study is 262 percent. This is a nonsensical number, but it’s a very big one in the dataset’s biggest study—so when Pontzer and Trexler calculate a weighted average of percent compensation, this single ersatz number is what skews the results.

I’ve gone into a lot of detail here, and there are many more nuances that could be debated further, e.g. about how the data should have been analyzed and whether the weight-loss study should have been included in the first place. But the bottom line, to me, is in the graph above. The abstract’s primary claim is that aerobic exercise only increases your energy expenditure by ~30 percent of what you’d expect. That’s simply not what the data shows.

The message I’m trying to convey here isn’t that this study is full of crap. I actually think it’s really interesting, and I still chose to write about it, though I omitted the problematic 30 percent claim. It’s that the full picture of any scientific debate is almost always more complex than what you get from skimming abstracts. It’s always worth checking out the actual data.

Other Stuff

My other recent Sweat Science column takes on a similarly tricky debate, on whether poor sleep raises your risk of injury. The 2017 bestseller Why We Sleep famously cropped a graph to make the case look stronger than it really was. Now a new study wades into the debate, adding further evidence of a sleep-injury link, but it’s far from a slam-dunk case.

In the Globe and Mail, I wrote about SMART goals: specific, measurable, achievable, relevant, and time-bound. It’s a popular approach to fitness goal-setting, but some researchers are pushing back. One alternative is open goals (see how many steps you can take, rather than aiming for, say, 10,000), which seem to work better than closed goals in certain contexts.

For an essay in Big Think, I took on the question of whether we’re approaching the end of world records. I draw a distinction between “biological” and “technological” progress (we tend to value the former and disparage the latter), but ultimately argue that the nature of human limits isn’t entirely dictated by either.

Finally, if you’re looking for audio entertainment, I’ve had a few fun conversations recently, including with sports psychologist Stu Holliday for the Focused Mind Podcast and with Lawrence and Mat on the Secret Life of Dads Podcast. Also, I’m beginning to dip my toes tentatively into the world of video: to start, I made a two-minute clip on why biathlete Sturla Holm Lægreid’s crazy post-Olympic-medal confession of infidelity was probably chemically fueled by the mother of all runner’s highs.

Thanks for reading, and let me know what you think in the comments below!

Alex Hutchinson

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VO2max measures how much oxygen you can inhale, deliver to your muscles, and use; it’s the gold-standard quantification of aerobic fitness. Back in 2019, I wrote about a journal article reporting a new VO2max record in another Norwegian athlete, the cyclist Oskar Svendsen. His reading was 96.7 ml/kg/min, eclipsing the previous unofficial record of 96 ml/kg/min set by yet another Norwegian athlete, cross-country skier Bjørn Dæhlie, in the 1990s.

Blummenfelt’s value has only been reported on Instagram, where peer review can be vicious but isn’t known for rigour. Numerous scientists have posted their own opinions of the result, including Jeroen Swart, Jem Arnold, and Stephen Seiler. The key detail many of them zeroed in on: the screen also showed an RER value of 0.93. RER is respiratory exchange ratio, which is the ratio of how much carbon dioxide you’re exhaling divided by the amount of oxygen you’re consuming. With a little math, this ratio tells you how much carbohydrate versus fat you’re burning. It’s also used to confirm that you’ve really reached VO2max, as opposed to giving up early because you’re either unable or unwilling to keep pushing to exhaustion.

In theory, VO2max readings are supposed to reach a “plateau,” levelling off even as you keep increasing the pace. In practice, not everyone’s data shows a plateau before they give up. Physiologists have been arguing for years about how to verify that you truly hit max. One of the criteria sometimes used is RER: it needs to be above (depending on who you ask) 1.00, 1.10, or 1.15. This is because high-intensity exercise starts producing lactate, which sets off a cascade of reactions that produce extra carbon dioxide.

The RER threshold isn’t perfect, because there can be variation in maximal RER values. But in general, if your RER is below 1.00, the assumption is that you quit early and your true VO2 max value is higher. That’s what makes Blummenfelt’s measurement so bizarre: it’s super high, but seemingly should be even higher. Still, human physiology is complex, and champion athletes like Blummenfelt are, by definition, one-of-a-kind. We have no idea what exercise protocol they were using, or whether other factors like dietary manipulations might be affecting the results.

When I was digging into Oskar Svendsen’s value seven years ago, several scientists in Norway expressed the opinion that Bjørn Dæhlie’s previous “record” was a dubious reading that his team had decided to leak to psych out his opponents. Similarly, it’s not hard to imagine Blummenfelt and his team enjoying the furor they’ve kicked up with their Instagram post. But unless their data shows up in a peer-reviewed journal, Svendsen is still the record-holder. Blummenfelt, meanwhile, can console himself with his Olympic gold medal and Ironman world titles—and the rest of us can use the incident as a reminder of which outcomes matter and which ones don’t.

Outtakes

A few quick hits on recent studies that I haven’t written about elsewhere:

The Crazy (and a Little Bit Scary) Physiology of Freediving

I got fascinated by freediving research when I was working on the “oxygen” chapter in Endure. I couldn’t believe that someone could hold their breath for more than 11 minutes, and found the various adaptations the body makes during dives (like squeezing the spleen to release extra red blood cells) very cool. But I also came across some hints that repeatedly depriving your brain of oxygen can have long-term consequences.

A big new review of freediving research in the European Journal of Applied Physiology, from researchers in Italy, brings together the current state of the art on freediving research. There are a bunch of interesting nuggets in there, like the observation of a freediver whose arterial oxygen levels dropped to 25 percent during a deep dive. For context, the values in a group of climbers near the summit of Everest at 8,400 metres ranged between 34 and 70 percent, which were considered “among the lowest ever documented in humans.” But it’s the evidence—still very limited—of neuron damage and lasting cognitive impairment that sticks in my mind.

How Do You Know If Altitude Training Will Work for You?

Altitude training is now considered all but essential for elite endurance athletes, but there are still doubters in the scientific world. The question isn’t whether it works in theory, but whether you can count on it working in practice. Studies tend to find that some athletes return from altitude training camps with a boost in red blood cells, and others don’t, so there’s great interest in figuring out how to predict in advance who is likely to benefit.

That’s the focus of a new study, also in the European Journal of Physiology, in which 15 German national team athletes did three weeks of altitude training by living in an “artificial altitude house.” Blood tests picked up two key pre-camp signals of who would respond best to altitude: healthy immune function (as measured by levels of various types of white blood cell) and iron status (as indicated by a hematocrit above 42.5 percent).

Why Cycling Is a “Perfect Storm” for Bone Health

The UCI, cycling’s governing body, sponsored a major sports nutrition research project, and one of the outcomes was this paper on bone health among cyclists. They suggest that cycling creates a “perfect storm” of overlapping risk factors: the lack of jarring impacts, prolonged periods of calorie deficit, self-selection of naturally skinny people, and more subtle metabolic shifts that occur during prolonged exercise, like a drop in calcium levels that promotes bone weakening. The solution: eat enough to fuel your training, particularly carbs, and also make particularly sure to get enough protein, calcium, and vitamin D. Relatively brief bouts of jump training can also stimulate bone strength.

Sweat Science Columns in Outside

A couple of recent columns:

What the New Study on Exercise and Longevity Really Tells Us: Harvard scientists find that exercise variety is good but not too much and only certain types. Take the findings with a grain of salt.

This is a deep dive into a study that got a lot of attention in both mainstream and social media last week. My key message is about the dangers of “statistically adjusting” epidemiological data to effectively erase the impact of exercise on parameters like BMI, blood pressure, and cholesterol, and why that creates the illusion of a plateau in the longevity benefits of exercise.

The 3 Steps This Year’s Olympic Athletes Are Following to Avoid Illness: Staying healthy is key to the quest for glory in Milano Cortina, so athletes are deploying the latest science.

A look at the latest data on avoiding exposure, boosting immunity, and fighting infections after they start. TLDR: if you really want to stay healthy for an important event, your best bet is probably masking up.

Thanks for reading! And if you have comments or questions, please use the button below.

Alex Hutchinson

To support my work, check out my latest book, The Explorer’s Gene: “science writing at its very best, with something fascinating on every page,” according to David Epstein.

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The inspiration for this comes, in part, from a new article I just wrote for The Atlantic (gift link) about the role of luck in athletic success. In a nutshell (as Joe Baker and Kathryn Johnston of the University of Toronto point out in a recent paper): if a contest depends 49% on talent, 49% on training, and 2% on luck, it generally takes excellent luck in addition to good talent/training in order to win.

One of the rabbit-holes I went down while reporting the luck article was on threshold effects. Say you’re a scientific granting agency. You get 100 grant applications which your reviewers rank from 1 to 100. You fund the top 20. Given the subjective nature of grant reviews, you can’t reliably say that the 20th-ranked application is truly “better” than the 21st-ranked application. Yet studies show that the bottom-ranked grant recipient will go on to have a more successful career than the top-ranked non-recipient. The grant itself (or lack thereof) altered their trajectories, even though their merit at that moment was essentially the same.

All of this is a long-winded way of saying that I think the studies below are interesting—and in some cases may even be more interesting to you personally than the ones I ended up writing about!

Outtakes

Supershoes and explosive power: Researchers at Brigham Young University had volunteers complete two 60-minute runs in either a regular running shoe (Saucony Kinvara) or a carbon-plated supershoe (Saucony Endorphin Pro 3). Two interesting things happened. One is that “VO2 drift”—the gradual increase in how much energy it takes to sustain a given pace over the course of a run—was lower in the supershoe. The other is that the runners were able to jump higher after running in supershoes—that is, their jump force didn’t decrease—indicating less neuromuscular fatigue. It’s not entirely clear why this happens, but it’s good news if you need to be able to sprint at the end of a race.

Heat makes refueling harder: This study, from researchers at Loughborough University, involved 100-minute runs in either warm or hot conditions, while drinking 60 grams per hour of carbohydrate in sports drink. In the hot condition, the runners burned 20 percent less of the carbohydrates they drank, even though they stayed fully hydrated, which meant they had to deplete their stored carbs more quickly. The takeaway is that when it’s hot, you’ll be more likely to run low on fuel. Maybe you can fight that by fueling more, if your stomach can handle it—but it’s also another good reason to adjust your pace expectations on hot days.

Running on a cambered road: Winter, for me, means reluctantly having to move some of my running from trails to roads—which means running on cambered surfaces, with a typical slope of 3 to 6 degrees to facilitate drainage. Everyone knows this isn’t ideal, and if cars didn’t exist we would alternate which side of the road we ran on. In practice, it’s a necessary evil that hasn’t been studied much. Enter this study from Westmont College. They tested runners on a treadmill sloped sideways at either 0, 3, or 6 degrees, and measured a bunch of metabolic and biomechanical outcomes. The short version: it doesn’t take any extra energy to run on a camber, but it does change knee and trunk movement and muscle activation patterns.

Intakes

Those were the studies that didn’t make the cut, so just imagine how fascinating the winners are! Here are the Sweat Science columns from Outside since my last newsletter.

Can You Adapt to Being Dehydrated?

New research on drinking during exercise is challenging old beliefs.

Why Some People Put on More Muscle Than Others

Scientists confirm that your mileage may vary in how you respond to workouts, but everyone benefits in the end.

Why Threshold Is More Important Than Max Heart Rate or VO2 Max

Choosing your pace based on the physiological transition from easy to hard is more effective than calculations based on maximum heart rate, research shows.

Why Science Says to Pick the Running Shoe That Feels Most Comfortable

New research backs this approach to avoiding running injuries.

Why Ketones Might Ward Off Altitude Illness

New research suggests that ketone drinks can raise oxygen levels in the blood.

Why Runners Get Lightheaded When They Stand Up

New research suggests it’s actually not about your heart.

Other stuff

Every December, I write a column for the Globe and Mail forecasting some fitness trends for the upcoming year. I’ve been doing this for more than a decade, which makes it an interesting exercise. (“High-intensity intervals? No, wait, that was one of the trends in 2009… and 2014… and 2021…”). My article is behind a paywall, but for the record, this year’s picks were: slowing down (i.e. what runners in the 1960s called LSD, or long slow distance); calorie counting (thanks to the rise of doubly-labeled water for measuring energy expenditure); shortcuts (a perennial favourite, epitomized this year by xenon for climbing Everest); and running (the Third Boom is here!).

That’s all for this time. Let me know in the comments if including outtakes is useful, or if that level of info is too shallow to be worthwhile.

Thanks for reading,

Alex Hutchinson

In reality, The Explorer’s Gene grew directly from my previous book, Endure. In the latter, I was interested in how we push our limits; in the former, I’m grappling with why. There are some endurance-specific stories in there: speedskater Nils van der Poel’s decision to overhaul his training in what I called “one of the most radically unconventional experiments in the annals of Olympic sport”; the mythologist’s Joseph Campbell’s little-known career as one of the top half-milers in the world, hero of the 1926 Penn Relays and just a second off the world record at the time. But I’ve been pleased to hear from longtime readers that they also see the more subtle underlying connections between the themes of exploration and endurance.

If you haven’t had a chance to read it yet, I hope you’ll check it out! It’s currently 44 percent off on Amazon.com (just $18), available at local bookstores everywhere, and you can find links to other retailers around the world here. Thank you for supporting my work.

The Top Ten!

On a semi-related note, the end of the year is also a time when I take a look back at the topics I’ve covered in my Sweat Science column for Outside. I write four columns a month, which means I end up covering a surprisingly wide range of topics (you can scroll through the whole list here). I don’t ask for or receive any data on which articles attract the most readers—I worry that checking that data will tempt me to start writing more for clicks rather than following what seems interesting to me. But at the end of each year, I do ask what the ten most-read articles were. It’s rarely the ones I would have predicted! Here’s that list for 2025:

#10: The 2025 Sweat Science Summer Book List

A selection of (mostly) new titles for fans of science, endurance, fitness, and adventure

#9: What an ‘Alone’ Fan Learned Backpacking in ‘Alone’ Country

The North Coast Trail, on Vancouver Island, takes you deep into the territory where several seasons of the reality show were set

#8: Does Exercise Really Benefit Your Mental Health?

Scientists take a closer look at the studies supporting links between physical activity and mental health and ask: is the evidence any good?

#7: Here’s Exactly What It Takes to Run—And Then Recover From—100 Miles

Physiologists track the calories burned and fluids consumed during a mountain ultra

#6: How Many Carbs Do You Really Need to Maximize Endurance?

It’s either way more than you think or way less than you think, depending on which scientists you listen to

#5: Puma’s High-Tech New Supershoe is Here—and It’s Already Turning Heads

The Fast-R Nitro Elite 3 claims to offer the biggest improvements in running economy since the Nike Vaporfly took the world by storm eight years ago.

#4: Why Athletes Should Think Twice About Vitamin D Supplements

A new study finds athletes with higher vitamin D levels are stronger, but the big picture remains murky

#3: Why Increasing Your VO2 Max Might Boost Your Brain

Two new studies add fresh data to the debate about exercise and brain function

#2: Why Steeper Is Cheaper for Climbing Hills

New data suggests that the most efficient uphill slope is steeper than you think

#1: How to Train Your Physiological Resilience

Scientists tackle the challenge of maintaining qualities like high VO2 max and good running economy even when you’re tired

Thanks, once again, for reading and supporting my work – I’m hugely grateful, and I’m looking forward to digging back in for 2026. But first, the holidays: here’s hoping you have a restful and enjoyable season.

Alex Hutchinson

Of course, I also slipped my own new book, The Explorer’s Gene: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, onto the list. It’s a deep dive into the science and psychology of why we’re drawn to figuring out what’s over the horizon. I liked the warning that The Guardian’s Charlie Allenby added when he included the book in his Christmas gift guide: “reading it has laid the foundations for attempts at even more ridiculous fitness challenges and the early onset of my mid-life crisis.” If I can help spur a few more people into taking on seemingly ridiculous challenges, I’ll consider the book’s mission accomplished. You can find links to order from various places here; thanks for your support, which makes a big difference to my ability to keep doing this work!

Another study I wrote about for Outside looked at the effects of exercise on people being treated for colon cancer. The short version is that getting people to add the equivalent of 2.5 hours a week of brisk walking dramatically extended their lives and lowered their likelihood of cancer recurring. But what really caught my eye was that this wasn’t just another observational study. It was a randomized controlled trial whose execution spanned more than 17 years. One of the authors told me that, as far as he knows, it’s the first randomized to trial to show that exercise extends life in any context! Studies like these aren’t easy to pull off, but they’re hugely important for showing the power of exercise.

I also covered the results of the largest ever study to demonstrate that mental fatigue impairs physical performance, and a new attempt from the American College of Sports Medicine to define universal exercise zones that cover both aerobic and resistance exercise and work for serious athletes and as well as novice exercisers. The middle zones (Low, Moderate, and High) are defined based on metabolic thresholds for aerobic exercise and “reps in reserve” for strength training. The extreme zones (Very Low and Very High) are harder to delineate. It’ll be interesting to see whether they catch on.

In more somber news, my alma mater, McGill University, announced that it was cutting 25 of its 44 varsity teams, including track and field. I wrote an op-ed for The Globe and Mail (link for subscribers only) comparing my experiences in three very different university sports worlds: the British version, where students run the show and mostly fund themselves; the American version, where student-athletes are provided with impressive resources and encouraged to prioritize their sport; and the Canadian version, which has traditionally been somewhere in the middle. There are arguments for and against each of these options, but my main contention is that, if Canadian institutions are either unable or unwilling to fund American-style college sports, they should at least consider the British model rather than eliminating sports entirely.

Thanks for reading – and if you have suggestions for books I should add to my own holiday reading list, please put them in the comments below!

Alex Hutchinson

Some topics I’ve been thinking and writing about in recent weeks:

· Fueling

My editor at the New York Times asked me to sum up the science on whether people need to refuel during exercise, which is one of those topics that’s hard to draw a clear border around. “If a player needs a gel during a typical training session, it usually means they didn’t prepare properly,” pro soccer nutritionist Tom Shaw told me. I tried to address the obvious question of when fuel becomes a potentially limiting factor (i.e. somewhere between the 100-metre dash and the marathon!), but the most important point I wanted to make was that it really depends on your goals. “Are you eating for performance or for overall health?” a scientist named Barry Braun asked me. “Because you make some different choices depending on the primary goal.” You can read the whole article via this gift link.

· Broccoli shots

For Outside, I dove into the hottest new supplement in the endurance world. Nomio is a shot of liquid extracted from the equivalent of about six pounds of broccoli sprouts, with wide-ranging claims: it lowers lactate levels, reduces inflammation and oxidative stress, boosts mitochondria, and so on. An impressive roster of Olympic champions and other pros already swear by it even though it was only released earlier this year. And the science behind it is… more interesting than I expected. Details here.

· Thyroid function

I also wrote about a new hypothesis for how REDs (relative energy deficiency in sport) develops. The gist: the combination of hard training and inadequate fueling raises cortisol levels, which suppresses thyroid hormone levels, which in turn leads to a cascade of metabolic and hormonal problems. It’s the thyroid link that caught my attention, given past controversies about endurance athletes with “low but normal” thyroid hormone levels and the alleged misuse of thyroid medications in Alberto Salazar’s Nike training group. Details here.

· My favourite gear

Finally, something a little different. My Outside editors asked me to put together of list of fitness and adventure gear that I swear by. For reasons that I’ve explained in previous newsletters, I rarely do product reviews. I’m inherently distrustful of even my own subjective opinions, especially if the products are being provided by the manufacturer. But in this case, the ask was for products that I already own and have been relying on for years. It was fun to think about which of my possessions have stood the test of time, from my Timex Ironman watch to my Tracksmith base layer to my trusty Tilley hat. Full list here.

In other news, I’ve had some fun podcast conversations recently. My episode with Shelby Stanger for REI’s Wild Ideas Worth Living podcast is a nice tight (half-hour), thoughtfully edited intro to the ideas I explore in The Explorer’s Gene. With endurance legend Rebecca Rusch, a.k.a. the Queen of Pain, I had a looser and more digressive conversation about doing hard things and how our relationship with that drive changes over time. And I loved batting ideas around with beloved Canadian radio personality Gill Deacon, whose upcoming book on embracing uncertainty dovetails with my own book.

Speaking of exploring the unknown, I’ve spent the past week preparing for an upcoming talk that’s very different from my usual fare. I’ll be giving the 2025 Cameron Hollyer Lecture hosted by the Toronto Public Library’s world-famous Arthur Conan Doyle Collection. The title of the talk is “Conan Doyle’s Lost World: Filling in the Blank Spaces on the Map,” and it will take place on Saturday, November 29 at 2:00 p.m. at the Toronto Reference Library. If you’re in town, come and hear what Doyle (and I) have to say about blank spaces, armchair exploring, and the pursuit of “useless” knowledge!

Thanks for reading,

Alex Hutchinson

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Back in 2019, there were a bunch of headlines about scientists discovering “the ultimate limit of endurance.” Not surprisingly, the headlines were overselling it a bit, but the research they described really was interesting: evidence that there’s a limit to how many calories we can digest—about 2.5 times our resting metabolism—and that this limit is what ultimately constrains multiday endurance challenges.
 
That claim was controversial, and to the credit of the scientists involved, they’ve continued to try to test it. A new study that I wrote about for Sweat Science takes calorie measurements from a few dozen ultrarunners during extraordinary feats like FKT attempts on the Appalachian Trail. The evidence suggests it’s hard to exceed the 2.5 limit by much, even for elites. But there may be even more data to come. After I shared my article on social media, ultrarunning legend Kilian Jornet chimed in to say that he’s taken “doubly labeled water” data (the gold standard for calorie measurement) during recent challenges like his States of Elevation project. Amazingly, he reports burning 5.45 times his resting metabolism without losing weight. The takeaway: to learn about the extremes of human metabolism, we need to study extreme outliers!
 
Other research I’ve covered recently in Outside:
 
Yell This, Not That: The Science of Cheering That Works
Turns out there’s a science to good cheering, and I’ve been doing it wrong
 
The Bare Minimum Food and Water You Need to Survive
“Extreme environmental physiologists” weigh in on what the human body really needs
 
… and in the Globe and Mail:
 
Strength and Endurance May Not Be Enemies After All
Contrary to conventional wisdom, endurance training may actually enhance strength in some contexts (and vice versa)
 
***
 
Meanwhile, in the real world, I’ll be appearing at the Ottawa International Authors Festival this Saturday, October 25, at 11:30 a.m. I’ll be in conversation with host Sarah Everts—particularly appropriate given that she was the author of a great book on the science of sweat. Consider it a sweat science summit! Details and tickets here.
 
In the virtual world, I had a particularly interesting podcast conversation with Ryan Murdock for his Personal Landscapes show. Ryan is a travel writer in the lofty spirit of Paul Theroux (one of his previous guests) who had just finished a solo journey along the Haute Route of the Pyrenees. We had a lot to talk about. I also had a return visit with Mark and Todd of the Runegade Podcast, chatting about The Explorer’s Gene.
 
Finally, a housekeeping note: I’ll be moving this newsletter from Mailchimp to Substack in the coming weeks. I’m not planning any changes to the newsletter or to put up a paywall or anything. Moving to Substack will save me a few thousand bucks a year, which is certainly nice. But the real motivation for the move is that Substack will have a comments section in the web and app version of each newsletter. I often get interesting questions by email about topics I’ve written about, and I think those discussions will be of interest to many readers. There was a time, a decade or so ago, when Twitter offered a space for those conversations; I’m hoping Substack can provide a new venue.
 
If you’re currently subscribed to the newsletter, you don’t need to do anything. You should receive a welcome email when I make the switch, but other than that it will be (fingers crossed) business as usual.
 
Thanks for reading!
 
- Alex Hutchinson

Nothing generates more controversy in the sports science world than supplements. When my editor at the New York Times recently asked if I’d like to write about them, my response was: They don’t work, other than a very, very short list put together by the International Olympic Committee a few years ago. She said “Okay, write that.” So that’s basically what my new article says.
 
It’s a little more complicated than that, of course. There’s a seemingly inexhaustible supply of promising supplements beyond the five items on the IOC list, often with solid-looking science and prominent athletes who swear by them. If I look at the evidence in isolation, it’s convincing. But I’ve reluctantly concluded over two decades of covering this field that even the most promising results often turn out to be unrepeatable. After all, as I noted in the article, “a recent attempt to reproduce the results of 25 major studies in sports and exercise science was successful in just seven cases.”
 
I can’t predict the future, so I don’t know which new supplements, if any, will be considered evidence-backed a decade from now. The truth is that if I were vying for an Olympic medal, I’d probably lower the evidence bar, Lloyd Christmas-style, and try some things that aren’t fully proven. You might choose to do the same—and that’s fine, as long as you’re doing it with your eyes open.
 
Or you might skip it entirely. Of the five supplements on the IOC list—caffeine, creatine, baking soda, beta alanine, beet juice—the only one I’ve tried is beet juice, and I only tried that once to see how it tastes. That’s partly a journalistic decision: there are lots of people who write about their personal experiences with training aids, so I try to stick to evaluating the evidence. And it’s partly about what I’m looking for when I train and race these days, which is less about times and competition with others than it was when I was younger. That’s not a condemnation of pre-race coffee; it’s just a reminder that these are optional extras, and you can choose to ignore them if you want!
 
***
 
Other topics I’ve covered recently:
 
What Ultra-Endurance Athletes Know About Coping With Pain (Globe and Mail)
Researchers surveyed the vast literature on how ultra-endurance athletes handle the inevitable discomfort of their sport, and distilled the findings into a few key concepts including interoception, acceptance, cognitive reappraisal, and locus of control.
 
For Outside:
 
The Hestia Is a Portable Telescope for Your Next Backcountry Adventure
I took this lightweight, battery-free scope into the wilderness to test its stargazing potential.
 
They Said Xenon Helped Them Set a Record on Everest. Now Scientists Are Questioning If It Really Had an Impact.
An expedition that summited Everest in less than a week sparked interest—and skepticism—about the benefits of the gas.
 
What an ‘Alone’ Fan Learned Backpacking in ‘Alone’ Country
The North Coast Trail, on Vancouver Island, takes you deep into the territory where several seasons of the reality show were set.
 
How Muscle Elasticity Affects Performance and Recovery
New research around muscle elasticity offers some surprising insights for marathon runners—and could explain how "super shoes" actually work.
 
***
 
Finally, a few logistical notes. In the last newsletter, I mentioned an upcoming talk in Regina. I ended up getting sick and having to postpone the talk. The new date is Thursday, October 16.
 
I’m also really looking forward to a live online Q&A with the inimitable running author Adharanand Finn, which will take place at 3 pm Eastern time on Wednesday, October 8 (details and tickets here). Adharanand is the author of a trifecta of exceptional running books: Running With the Kenyans, The Way of the Runner, and The Rise of the Ultra Runners.
 
And speaking of books, Robert Glazer’s new one, The Compass Within, will be out next month. Robert is a consistently interesting and thought-provoking business writer whose Friday Forward newsletter I’ve subscribed to since 2018, and I recently sat down with him to chat for his Elevate podcast; that episode should be out soon.
 
Thanks for reading!
 
- Alex Hutchinson

Quick heads-up that the e-book edition of The Explorer’s Gene is on sale for just $1.99 across all e-book sites (that’s in Canada and the U.S., not sure about other markets). The audiobook edition is also on sale for $6.99. The sales last until this Sunday, August 31, and there will never be a better price, so it’s a great time to pick up a copy.
 
Next stop on the book tour is next week in Regina, Saskatchewan. I’ll be speaking at the Regina Public Library on Wednesday, September 3, at 7 p.m. in advance of the Queen City Marathon. You can register here.
 
Here are the Sweat Science columns since my last newsletter:
 
What You Need to Know About the New Data Linking Marathons to Colon Cancer
Preliminary findings suggest marathoners and ultramarathoners may have a higher risk of abnormal colonoscopy findings, but previous studies paint a different picture
 
New Evidence That Long, Slow Distance Is the Key to Endurance Success
Top cyclists on the women’s World Tour do better when they rack up more easy training, a new analysis finds
 
How My iPhone’s New Satellite Messaging Function Kept Me Connected in the Backcountry
Instead of a dedicated satellite messaging system for emergencies, I decided to trust the new feature on my phone—and it worked
 
How Collagen Might Boost Your Explosive Strength
A new study bolsters the claim that collagen supplements can help remodel your tendons and muscles
 
After the Biggest Doping Bust in Years, What’s Next?
Now that the fastest marathoner in history, Ruth Chepngetich, has been caught, is it time give up and let athletes dope?
 
Thanks for reading!
 
- Alex Hutchinson

A quick mid-summer update: I’m heading out tomorrow to hike the North Coast Trail on Vancouver Island with my family, so I’ll be offline until early August. On the way to the trail, I’m stopping in Victoria for a talk/conversation with Chris Kelsall at Frontrunners. That’s this Friday, July 25, at 6pm: details here.
 
My latest Sweat Science columns for Outside:
 
A New Theory Explains Why Exercise Makes Us Tired
Scientists draw on the cognitive science idea of “predictive processing” to explore what’s happening in our brains during prolonged efforts
 
Here’s Exactly What It Takes to Run—And Then Recover From—100 Miles
Physiologists track the calories burned and fluids consumed during a mountain ultra
 
The Most Common Trail Running Accidents—and What We Can Learn From Them
Patterns emerge in a database of more than 100 trail-running fatalities
 
In the Globe and Mail, I wrote about exercising in polluted air—unfortunately a very topical question once again this summer—and how to minimize the negative effects.
 
On the book promo circuit, I’ve had a few fun conversations recently, including with Callum Jones for his Footprint newsletter; Elizabeth Weingarten for her Time Travel For Beginners newsletter; and Floris Gierman for the Extramilest Show. To order The Explorer’s Gene, you can find links from various retailers around the world here.
 
Thanks for reading!
 
- Alex Hutchinson

Book tour note: free tickets are now available here for my upcoming talk at Frontrunners in Victoria on Friday, July 25. Come and say hello!
 
My big focus over the last few weeks was covering Faith Kipyegon’s attempt to run the first women’s sub-four mile, in a Nike-orchestrated exhibition event in Paris called Breaking4. My immediate post-race report is here; my subsequent reflections on what we should take away from the event—lessons on drafting and pacing, musings on the role of exhibition events, mind vs. body in the pursuit of endurance, and how we celebrate female athletes—are here.
 
When Kipyegon crossed the finish line, the time that flashed on the clock was 4:06.91. Then it was quickly adjusted to 4:06.42, which is the time Nike announced to the world. It turns out that the latter time was from the moment Kipyegon crossed the start line, rather than when the starting gun fired, effectively subtracting her reaction time.
 
These events—first Eliud Kipchoge’s Breaking2, and now this one—have generated a lot of strong reactions. Some people love them, some hate them, and I think most (including me) have mixed feelings. The events inevitably involve breaking some rules; how I feel about that depends on which rules are broken (I have zero interest in, say, a downhill-on-rollerskates mile), but also on the level of transparency about those rules. Before the race, lots of people speculated that giving Kipyegon a running start could save some time, and I would have considered that a reasonable way of setting up the race. But Nike never acknowledged or mentioned it until well after the race, and that leaves a bad taste in my mouth. We can be glad, I guess, that it wasn’t the difference between 4:00.xx and 3:59.xx. And we can look forward to seeing how Kipyegon fares on Saturday at the Prefontaine Classic, where she’ll be targeting her own world record in the 1,500 meters under normal record-eligible conditions.
 
A couple of other recent Sweat Science topics:
 
The 2025 Sweat Science Summer Book List
A selection of (mostly) new titles for fans of science, endurance, fitness, and adventure
 
Why a NASA Fatigue Questionnaire Is More Accurate Than Your Wearable Tech
To figure out how hard your workout was, high-tech isn’t necessarily better, according to new research.
 
I also wrote in the Globe and Mail about an interesting new review paper from some leading sports nutritionists about the role of dietary fiber, which they dub "the forgotten carbohydrate in sports nutrition recommendations." My article is for subscribers only, but the full review paper is freely available here. The gist: aim for 30 grams of fiber per day, and at the very least make sure you're getting 20 grams.

Thanks for reading, and please check out the links to order my new book The Explorer’s Gene from various retailers around the world here.
 
- Alex Hutchinson

 

Two upcoming book events to flag: Tuesday, June 10, in Toronto at Rotman School of Management (tickets here); and Thursday, June 12, in Vancouver at Forerunners, where I’ll be sharing the stage with Chris Napier of Simon Fraser University’s Run Lab, who will be discussing his research from Lululemon’s 6-day FURTHER ultramarathon (RSVP here). Come and say hi!
 
There’s been a big furor over the recent news that four British climbers inhaled xenon gas as part of a plan to climb Everest in just one week door-to-door from Britain. What struck me is the parallel between that controversy and the one surrounding Faith Kipyegon’s upcoming attempt to run the first women’s sub-four-minute mile in a Nike-sponsored exhibition race, using yet-to-be-revealed performance-boosting techniques. It’s like 1953 all over again, when Edmund Hillary and Tenzing Norgay scaled Everest for the first time using supplemental oxygen, and Roger Bannister just missed running the first sub-four (he’d do it a year later) with the aid of a lapped teammate pacing him all the way to the finish. I wrote about this historical echo, and what it tells us about the changing role of competition in our society, for The Atlantic (gift link here).
 
In the Globe and Mail, I wrote about why I’m trying to swear off turn-by-turn GPS directions from my phone: “On a superficial level, I was worried that the navigational centres of my brain were at risk of withering away. But the ubiquity of GPS also felt emblematic of a deeper shift in how we interact with the world and with each other these days: more passive, more automatic, more forgettable.” Read the whole thing here.
 
Finally, here are my recent Sweat Science columns for Outside:
 
Can You Get the Same Gains Without Lifting to Failure?
According to new research, keeping two repetitions in reserve is almost as good as maxing out every set of your strength routine.
 
New Research Says Endurance Athletes May Need as Much Protein as Weight Lifters
It’s not just about big muscles: scientists now believe that protein is also a recovery aid and even a fuel.
 
Inhaling Carbon Monoxide Could Boost Athletic Performance—But At What Cost?
A new approach to endurance training involves inhaling carbon monoxide—and is reviving old debates about dying to win.
 
Thanks for reading—and if you haven’t already, you can find links to order The Explorer’s Gene from various retailers around the world here.
 
- Alex Hutchinson

I’m currently on a train to Ottawa for a talk at the Royal Canadian Geographical Society’s Can Geo Talks series. It’s tomorrow (Wednesday, May 14) at 7pm, and tickets are free – come say hello! Next up is an evening at The Runner’s Shop in Toronto on Tuesday, May 20; details and tickets here. After that, it’s on to the Outside Festival in Denver on May 31 and June 1, where I’ll be leading on-stage conversations with legendary runners Scott Jurek and Hillary Allen. Details on further events here.
 
In my latest Globe and Mail column, I wrote something that you might think runs against my personal brand—an admission that running isn’t always best. It’s a column about new research on the cognitive benefits of “open-skill” versus “closed-skill” sports. Open-skill sports are those like soccer and hockey that require quick decisions in fast-moving and constantly changing environments. Closed-skill sports, on the other hand, tend to provide more repetitive and predictable challenges: think golf and, yes, running. The gist of the research is that kids who play open-skill sports score better than those who play closed-skill sports or no sports at all on cognitive tests, particularly in executive function: attentional control, working memory, resistance to distractions.
 
Of course, the boundaries between open-skill and closed-skill activities aren’t as rigid as you might think. Trail-running is much more unpredictable and cognitively engaging than, say, running on a treadmill. And there’s a separate body of evidence that aerobic exercise has other benefits for brain health. But I do think there’s something worth thinking about here about the benefits—and pleasures—of activities that engage brain and body at the same time. My column (behind a paywall) is here; the study abstract is here.
 
The Globe also ran a nice review by Emily Donaldson of The Explorer’s Gene, noting “expert storytelling” along with “a dizzying amount of multidisciplinary (anthropological, biological, neuroscientific, historical) research.” On the podcast circuit, I made an appearance on Chris Williamson’s Modern Wisdom show. I also had a really delightful conversation with Zoë Rom and Brendan Leonard (a.k.a. semi-rad, awesome cartoonist and author of books including I Hate Running and You Can Too) on The Trailhead Podcast, where I achieved a lifelong goal of slipping in not one but two T. S. Eliot references, which Zoë expertly volleyed.
 
On that note—thanks for bearing with me through all the book promo stuff. It’s a really important part of the book-publishing process: if I don’t sell books, I don’t get to write another one! That said, the initial burst of promo should be settling down soon, and I’ve got some great Sweat Science columns on tap. In the meantime, you can find links to order The Explorer’s Gene from various retailers around the world here.
 
Thanks for reading!
- Alex Hutchinson