According to Shakespeare, there are lessons and stories everywhere in nature鈥攐r, as he puts it, books in the running brooks, tongues in trees, and sermons in stones. I鈥檓 down with that idea. But in case the running brooks aren鈥檛 meeting your educational needs this summer, here are some suggestions for actual books to tuck into your backpack. (You can also look for more top picks on my holiday book list and last summer’s book list.)

Water Borne, by Dan Rubinstein

The tale of an epic wilderness voyage to鈥� New York City?! Rubinstein is a longtime outdoors journalist and avid stand-up paddleboarder, and in 2023 he set out to paddleboard from his home in Ottawa on a 1,200-mile loop via Montreal, New York City, and Toronto. His trip ends up being a fascinating tour through the varied waterways and communities of the Great Lakes region, a deep dive (sorry) into the health-promoting powers of being in and around water鈥攁nd also just an enjoyable and often funny read about a quirky and impressive trip.

Pushing the River, by Frank Bures

My own preferred mode of paddling is in a canoe, and Bures鈥檚 book adds to the surprisingly sparse ranks of canoeing literature. (Don鈥檛 @ me, I know there are some great canoeing books out there鈥攆rom Thoreau to Roy MacGregor to Adam Shoalts鈥攂ut not as many as the world deserves.) The central part of this story collection is a historical account of the 450-mile Paul Bunyan Canoe Derby, but for me the most engaging stories are Bures鈥檚 own adventures and the reflections they inspire: a voyage down the Mississippi from Minneapolis to his hometown, Winona; an unexpected dunk in hypothermic waters. Disclosure: I wrote the intro to this one.

How to Fall in Love with Questions, by Elizabeth Weingarten

In times of upheaval, we get a lot of books about how to handle uncertainty鈥攁nd, in many cases, how to embrace uncertainty. Weingarten, a journalist and behavioral scientist, thinks this advice is too pat. After all, being mired in uncertainty about important questions can be miserable. More worryingly, being too eager to resolve uncertainty鈥攚ith instant answers from AI or overly confident advice from wellness gurus, say鈥攃an lead us astray. This is a nuanced look at a complex topic.

Ballistic, by Henry Abbott

I first encountered Marcus Elliott in Charles Bethea鈥檚 epic 国产吃瓜黑料 story about 鈥渕isogis鈥� back in 2014. He sounded like an interesting dude, but I didn鈥檛 realize at the time what a major figure Elliott is in the world of injury prevention for pro athletes. That鈥檚 the topic of Abbott鈥檚 new book, which is part biography and part injury prevention manifesto. Elliott is a big believer in the importance of ballistic movements like jumping and landing, and also in the power of 3D motion analysis to pick up subtle signs of impending injury. My general take is that injury prediction is somewhere between really hard and impossible, but by the end of the book, I couldn鈥檛 help thinking, 鈥淢an, I鈥檇 like this guy to take a look at my running stride.鈥�

Adaptable, by Herman Pontzer

Pontzer is an evolutionary anthropologist at Duke University, and his new book is basically an account of how our bodies work as viewed through the lens of evolution. You might be familiar with his previous book, Burn, which covered the modern science of metabolism and calorie-burning. What makes both books worth reading is that Pontzer is exceptionally good at explaining science in a clear, rigorous, and entertaining way.

How Economics Explains the World, by Andrew Leigh

If Pontzer鈥檚 credo in Adaptable is 鈥渆verything makes sense when viewed through the lens of evolution,鈥� Leigh鈥檚 is 鈥渆verything makes sense when viewed through the lens of economics.鈥� Leigh is an Australian politician and government minister, as well as an accomplished ultrarunner and former economics professor. The subtitle of his new book is 鈥淎 Short History of Humanity,鈥� which captures its spirit nicely: it鈥檚 basically a fun and fast-paced history of civilization as seen from the perspective of economists.

Win the Inside Game, by Steve Magness

Longtime science-of-running fans will remember Magness as the author of the encyclopedic tome a decade ago. Before that, he鈥檇 been a 4:01 high-school miler and later a coach of college and professional runners. In recent years, though, Magness鈥檚 focus has broadened to performance in its broadest sense. He wrote a couple of performance-focused books with former 国产吃瓜黑料 columnist Brad Stulberg, and then the 2022 bestseller . Magness has always been an exceptional synthesizer, drawing connections across an impressively wide range of domains. His new book is more personal than his previous ones, drawing on his experiences as a whistleblower at the Nike Oregon Project, and seeks to guide the reader not just to performance but to fulfillment.

Out and Back, by Hillary Allen

In 2017, Allen fell 150 feet off a ridge during a mountain race in Norway. Her injuries were horrific. This book is her account of what happened after the accident. Spoiler: contrary to all predictions, she managed to return to the top levels of elite ultrarunning, and in fact her career continues to this day. The story itself, as a straightforward narrative, is fascinating. But what takes it up a notch is her attempts to understand what being an endurance athlete means to her鈥攂ecause you don鈥檛 fight back from an accident like that without a clear understanding of your whys.

North, by Scott Jurek

Jurek鈥檚 second book, after his 2012 bestseller , grapples with some of the same questions Hillary Allen鈥檚 book does. But instead of a mountain accident, he鈥檚 facing a more inexorable foe: aging. He was 41 when he set out to attempt to break the Appalachian Trail record, his career as a legendary ultramarathon champ fading out. Like Allen鈥檚 book, Jurek鈥檚 top-level narrative鈥攊n this case, the record attempt鈥攊s a great story on its own, full of improbable twists and impressive feats. But it鈥檚 the existential angst that kept me turning the pages.

Burke & Wills, by Peter FitzSimons

I spent the last five years writing a book about the science of exploring, which meant I read a lot of exploring stories. Among the most epic was the tale of the Burke and Wills expedition, the first to cross the interior of Australia. It鈥檚 by far the most famous Australian exploration tale, but relatively unknown outside the country. That should change: it鈥檚 a wild saga, a mix of adventure, fortitude, comedy (the first time I heard about the expedition was in a Bill Bryson book), and tragedy. For a long time the definitive account was Sarah Murgatroyd鈥檚 2002 book The Dig Tree, but FitzSimons鈥� 2018 book now holds that mantle.

The Explorer鈥檚 Gene, by Alex Hutchinson

You can also find out about Burke and Wills by reading鈥� my new book! They feature in a chapter that compares the exploration of Australia to the strategies mice use to explore water mazes: thigmotaxis, scanning, incursions, and so on. Burke and Wills used a strategy that鈥檚 very effective for crossing large expanses of unknown territory, but not so good for getting back home again. More generally, the book is about why we鈥檙e drawn to explore, how we do it, and what we get out of it鈥攖he perfect accompaniment for whatever adventures you have planned for the summer. Happy reading!

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If I told you that NASA has developed a radical new way of monitoring and quantifying your workouts, and that that method outperforms all others, you鈥檇 probably assume that it involves bleeding-edge science. There would be AI, and some sort of wearable or perhaps even injectable technology. It would be very expensive.

But you鈥檇 be wrong, for reasons that tell us something important about the quest to transform training optimization from an art into a science. A new study by Mattia D鈥橝lleva and his colleagues at the University of Udine compares different ways of assessing the 鈥渢raining load鈥� of different workouts鈥攁nd finds that a low-tech NASA questionnaire produces the most accurate results. The findings offer a reminder that outsourcing our training decisions to wearable tech algorithms 诲辞别蝉苍鈥檛 always outperform simply listening to our bodies. The research also raises a tricky question: is the workout that makes you most tired also the one that increases your fitness the most?

Why Does Training Load Matter?

The goal of training is to impose a stress鈥攁 training load鈥攐n your body that makes it tired in the short term but triggers adaptations that make it fitter in the long term. Going all-out in one workout isn鈥檛 constructive, even though it imposes a huge training load, because it leaves you too tired to train effectively the next day. The art of training is figuring out what mix of easy, medium, and hard workouts will enable you to accumulate the greatest possible training load over weeks and months without getting crippled by fatigue.

In its simplest form (as I discussed here), the training load of a workout is a combination of how hard you push and how long you push for. But the details get tricky. What鈥檚 the best measure for how hard you鈥檙e pushing? You could use pace, power, heart rate, heart rate variability, lactate levels, perceived effort, or other progressively more esoteric metrics. And how do you combine effort with duration? You can鈥檛 just multiply them together, because effort is nonlinear: running twice as fast for half the distance won鈥檛 produce the same training effect.

The , which is published in the International Journal of Sports Physiology and Performance, compares seven different ways of calculating training load. Four of them are variations on a concept known as TRIMP, which is short for 鈥渢raining impulse鈥� and is based on heart rate measurements, using equations that account for lactate levels, breathing thresholds, and other details. A fifth uses heart-rate variability, and a sixth uses a subjective rating of effort. (Most fitness wearables, by the way, likely use a combination of the above methods, though their exact algorithms are typically proprietary.) The seventh method is the NASA questionnaire, which we鈥檒l come back to.

The gold standard against which all these methods were compared is the 鈥渁cute performance decrement,鈥� or APD. Basically, you do an all-out time trial, then you do your workout, then you do another all-out time trial. Your APD is how much slower the second time-trial is compared to the first one, as a measure of how much the workout took out of you. Obviously this isn鈥檛 a practical way of monitoring training, because you can鈥檛 race before and after every workout. But for researchers, it鈥檚 a way of checking whether various methods鈥攊ncluding the seven they tested in this study鈥� correspond to the reality of how hard a workout is on your body. At the end, they were able to figure out which method was the most reliable predictor of training load.

What the New Study Found

D鈥橝lleva and his colleagues recruited 12 well-trained runners (10 men and 2 women) to test four different running workouts on different days:

• Low-intensity training (LIT): 60 minutes at a pre-determined comfortable pace
• Medium intensity (MIT): 2 x 12:00 at a moderate pace with 4:00 easy recovery
• Long high-intensity (HITlong): 5 x 3:00 hard with 2:00 recovery
• Short high-intensity (HITshort): two sets of 11 x 30 seconds hard, 30 seconds easy

The performance test was running at VO2 max pace until exhaustion. When they were fresh, the runners lasted just under six minutes on average. After the one-hour easy run, their APD was 20.7 percent, meaning they gave up 20.7 percent earlier in the post-workout VO2 max run. After the medium-intensity run, the APD was 30.6 percent; after the long intervals, it was 35.9 percent; after the short intervals, it was 29.8 percent.

So how well were each of the seven training load calculations able to predict this APD? The short answer is: not very well. Here鈥檚 a comparison of APD (on the left) and one of the parameters studied, which is called bTRIMP and is based on heart-rate measurements and lactate curves:

In fact, the relationships are completely reversed: the easiest workout according to bTRIMP produces the biggest APD in reality, and the workout ranked hardest by bTRIMP produces the smallest APD. All except two of the training load calculations the researchers measured have similar upside-down relationships. The two exceptions are heart-rate variability and the NASA questionnaire, which look like this:

The heart-rate variability measures, on the left, don鈥檛 tell us much, because they鈥檙e basically the same after each of the four workouts. (You can see some subtle differences, but they鈥檙e not statistically significant.) The NASA questionnaire, on the other hand, bears a striking resemblance to the APD data, and the statistical analysis confirms that it鈥檚 a good predictor. In other words, it鈥檚 the only one of the seven calculations tested that, according to this study, accurately reflects how exhausted you are after a workout.

So what is this questionnaire? It鈥檚 called the , or NASA-TLX, and was developed in the 1980s. It鈥檚 simply a set of six questions that ask you to rate the mental demand, physical demand, temporal demand (how rushed were you?), performance (how well did you do?), effort, and frustration of a task. You answer each of these questions on a scale of 1 to 100, then the six scores are averaged鈥攁nd presto, you have a better measure of how hard your workout was than your watch or heart-rate monitor can provide.

What the NASA Questionnaire Misses

These results don鈥檛 mean that we should all start recording NASA-TLX scores in our training logs. Questions like how hurried you felt don鈥檛 seem very relevant to running, or to training in general. What鈥檚 more significant about the questionnaire is what it 诲辞别蝉苍鈥檛 include: any measure of how long the workout was.

All the other training load measures rely on a combination of intensity and duration. But the effect of duration swamps the measurement: that鈥檚 why the bTRIMP graph above shows the 60-minute easy run (LIT) as the workout with the biggest training load. It鈥檚 really just telling us that it was the longest workout. The NASA-TLX, on the other hand, just asks (in various ways) how hard the workout felt once it was done. That turns out to be a better way of predicting how much slower you鈥檒l be after the workout.

There鈥檚 an implicit assumption in all of this discussion, though, which is that the workout that provides the biggest training load is the one that will improve your fitness the most. Is APD鈥攈ow much slower you get over the course of a single workout鈥攔eally the best predictor of fitness gains? It鈥檚 easy to come up with scenarios where that鈥檚 not true. If I sprain my ankle, my APD will be enormous, but that 诲辞别蝉苍鈥檛 mean I鈥檓 going to be an Olympic champion next month. Similarly, you can imagine workouts that would inflict a disproportionate amount of performance-sapping fatigue鈥攕teep downhill running, for example鈥攃ompared to their fitness benefits.

Perhaps what we鈥檙e seeing here is not so much 鈥済ood鈥� (NASA-TLX) and 鈥渂ad鈥� (TRIMP) measures of training load, but rather good measurements for two different types of training load. The APD and NASA-TLX mostly reflect how hard/intense/fast the workout was. TRIMPs and other metrics that incorporate duration end up mostly reflecting how long the workout was. There鈥檚 no reason to assume that these two parameters are interchangeable. It鈥檚 not just that you can鈥檛 get the same training benefit by going twice as fast for half as long. It鈥檚 that there鈥檚 no equation that makes fast running produce the same benefits as slow running. They鈥檙e two different physiological stimuli, and the smart money says you need both to maximize your performance.

So where does this leave us? I鈥檓 not anti-data, and I鈥檓 open to the idea that some of the newer metrics provided by wearable tech might reveal useful patterns if you collect them consistently. But if you strip training down to its bare essentials, these results suggest to me that there are two separate parameters that really matter: how long and how hard. And for now, I鈥檓 not convinced that we have any measuring tools that are significantly better than a stopwatch and an honest answer to the question 鈥淗ow did that feel?鈥�

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Back in 1969, naval researchers took blood samples from the crew of a Polaris nuclear submarine over the course of an eight-week patrol. Three-quarters of the sailors were smokers, so carbon monoxide levels were chronically elevated in the sealed confines of the sub. After a few weeks in this toxic miasma, the crew鈥檚 levels of hemoglobin, the crucial protein in red blood cells that ferries oxygen from the lungs to the muscles, had shot up by an average of 4.4 percent. Secondhand smoke had somehow turned the submariners into aerobic superstars.

This finding, along with others like it, was filed away for decades. After all, smoking destroys your lungs, so any performance benefits are outweighed by the harms. But then, last year, the idea exploded. Scientists published fresh data showing that huffing carbon monoxide could boost endurance. Other scientists responded with editorials warning against fooling around with a gas whose nickname is 鈥渢he silent killer.鈥� And headlines around the world trumpeted the news that 鈥攃onfirmation, seemingly, of the clich茅 that elite athletes will accept any risk in exchange for victory. The full story, though, is a bit more complicated.

The quest for endurance is, in part, about hemoglobin. More hemoglobin means more oxygen delivered to your muscles, which means you can run or ride or swim faster, for longer. Starve your muscles of oxygen in training and your body responds by secreting EPO, a hormone that stimulates the production of hemoglobin-carrying red blood cells. That鈥檚 how altitude training works: There鈥檚 less oxygen available, so your body produces more EPO to compensate. (It鈥檚 also why synthetic EPO is the banned drug of choice among endurance athletes.)

Virtually all performance-enhancing drugs are associated with health risks, and that hasn鈥檛 harmed their popularity.

When you inhale carbon monoxide, some of your red blood cells ferry molecules of it (instead of oxygen) around your body. Carbon monoxide attaches to hemoglobin and 诲辞别蝉苍鈥檛 let go, making those red blood cells unavailable to carry oxygen for many hours. It鈥檚 like altitude training in a bottle: Your body will sense the oxygen shortage and respond by producing EPO. But inhale too much and you won鈥檛 deliver sufficient oxygen to your heart and brain鈥攁nd once your hemoglobin is clogged with carbon monoxide, it鈥檚 not easy to reverse. Around 1,200 people die every year in the United States from deliberate or accidental carbon monoxide poisoning.

So carbon monoxide as a performance booster has been understood but mostly unspoken. It wasn鈥檛 until 2018 that the idea got more concrete. An initial study confirmed that deliberately breathing carbon monoxide boosted EPO. The next year, researchers in China, tasked with preparing their country鈥檚 athletes for the 2022 Beijing Winter Olympics, reported that college soccer players who inhaled the gas five times a week increased their hemoglobin levels. A , in which subjects inhaled the gas five times a day, reached similar conclusions. Most recently, a by researchers in Norway combined altitude training with twice-daily carbon monoxide inhalation for a synergistic effect.

But there hasn鈥檛 been a single verified report of an athlete actually using this technique. I reached out off-the-record to contacts in several elite endurance sports, as well as researchers in the field, and none of them had heard even rumors of real-life usage. The risk, so far, is theoretical. The headlines during the Tour de France referred to the use of small doses of carbon monoxide to measure hemoglobin levels. This technique has long been used in elite sport to check how athletes are responding to altitude training, but the doses are too low to boost performance. There is a gray area here: Once you鈥檝e got the carbon monoxide device in the team van, there鈥檚 a temptation to use it. But would elite athletes, these paragons of super-fitness, really take such a dumb risk?

Whether rational or not, we all accept nonzero risks in pursuit of goals.

It鈥檚 a fair question. In the 1980s and 鈥�90s, Chicago doctor Robert Goldman circulated a now-infamous series of questionnaires among elite athletes, asking if they would take an undetectable drug that would make them unbeatable for five years鈥攁nd then die of the side effects. Roughly half the athletes accepted the bargain, he reported. Goldman鈥檚 Dilemma, as it鈥檚 now known, is often cited as evidence of the modern athlete鈥檚 off-the-charts focus on winning, regardless of the costs. And indeed, virtually all performance-enhancing drugs are associated with health risks, and that hasn鈥檛 harmed their popularity. 鈥淵ou have guys who will go to the funeral of a friend who died from this stuff, come home, and inject it again,鈥� an anonymous Olympic runner told Sports Illustrated in a 1997 article about Goldman鈥檚 Dilemma.

But it鈥檚 not clear whether Goldman鈥檚 respondents were taking the question seriously, or whether attitudes have changed. Recent attempts to replicate Goldman鈥檚 results raise doubts. A 2018 study from Duke University estimated the 鈥渕aximum acceptable mortality risk鈥� that nearly 3,000 athletes would accept in exchange for the guarantee of Olympic gold. No one took the deal if it meant certain death. Depending on the sport and the level of competition, athletes were, on average, willing to accept somewhere between 7 and 14 percent risk of a fatal heart attack.

That鈥檚 still a big risk. But it鈥檚 comparable, the researchers point out, to the risks people say they鈥檙e willing to accept in exchange for other life-changing outcomes, like relief from their rheumatoid arthritis. And it鈥檚 not fundamentally different from the types of risk you might encounter on mountain expeditions, in extreme sports, or in the backcountry. Whether rational or not, we all accept some risks in pursuit of our goals. So it seems unlikely that the theoretical possibility of a fatal mishap will be enough, on its own, to dissuade athletes from trying to get a boost from carbon monoxide.

In February, the UCI, cycling鈥檚 international governing body, to boost performance, while the use of single doses to measure hemoglobin will still be allowed. This may seem like one of those wishy-washy compromises that鈥檚 almost impossible to enforce: the substance itself is permitted, but you have to promise you鈥檙e using it for the right reasons. But I think it鈥檚 the right call. Anti-doping agencies should, of course, be trying to catch unrepentant cheaters. But they also have a crucial role to play in setting broader norms about what risks we should or shouldn鈥檛 be willing to accept in pursuit of gold. Motivated athletes will do whatever the rules permit鈥攕o let鈥檚 not ask them to suck on a tailpipe five times a day, any more than we would lock them in a nuclear sub with a crew of chain-smokers.

This piece first appeared in the summer听2025 print issue of 国产吃瓜黑料 Magazine. Subscribe now for early access to our most captivating storytelling, stunning photography, and deeply reported features on the biggest issues facing the outdoor world.

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You鈥檇 have a hard time finding any serious endurance athlete in 2025 who thinks protein 诲辞别蝉苍鈥檛 matter. Gone are the carb-centric days of pasta and Gatorade and nothing else. But figuring out how much protein runners, cyclists, and other endurance junkies actually need鈥攁nd when they need it鈥攔emains a work in progress.

I鈥檝e grappled with these questions a few times recently鈥攊n a piece busting some common protein myths, and in another discussing the idea of maximum protein intake. But now a in Sports Medicine, from a research team led by Oliver Witard of King鈥檚 College London, offers a comprehensive overview of the current state of knowledge. Witard and his colleagues focus on two key questions. First, how much protein do endurance athletes need on a daily basis to stay healthy and optimize long-term training adaptations? And second, what role can the tactical use of protein play in speeding up short-term recovery and boosting performance?

Protein for the Long Term

Government guidelines currently recommend getting at least 0.8 grams of protein per kilogram of body weight (g/kg) each day. For someone who weighs 150 pounds, that works out to 55 grams of protein. For reference, a standard 5-ounce can of tuna has about 20 grams of protein.

There are two main problems with this guideline, however. First, it鈥檚 intended to be the minimum required to stay healthy, not the optimal amount to maximize performance. Second, it was formulated using a measurement technique that involves tracking the amount of nitrogen being consumed and excreted from the body, which some scientists believe underestimates protein needs. A newer approach called the 鈥�,鈥� which involves labeling one specific type of amino acid with a carbon isotope to see how quickly it鈥檚 burned, gives higher numbers and is also more practical for testing specific populations like athletes.

The usual argument for getting lots of protein is that it provides the building blocks鈥攁mino acids鈥攆or building new muscle. That鈥檚 important for strength training, but endurance athletes need it for other reasons. One is that these building blocks are used to repair the muscle damage incurred by hard training: the longer and harder you run, the more damage you incur, and more protein you presumably need for repairs.

During prolonged exercise, your body also starts burning amino acids for fuel. The amounts are generally small, and how much you burn depends on the nature of the exercise and what else you鈥檙e eating, but in some cases 5 to 10 percent of the fuel you need for a given workout is provided by protein. If you鈥檙e training hard, you鈥檒l need to eat extra protein to replace those losses.

There are some more subtle possibilities, too. Muscle isn鈥檛 the only part of the body that鈥檚 built from protein. One of the key adaptations athletes gain from endurance training is an increase in the amount of protein in the mitochondria, where cellular energy is generated. The more protein in the mitochondria, the more efficiently it creates energy. A few studies have sought to听 figure out whether eating more protein boosts the mitochondrial response to exercise. The results so far haven鈥檛 been convincing, but it鈥檚 still an open question.

Witard and his colleagues pooled data from various indicator amino acid studies to assess protein needs for endurance athletes under various conditions. Here are some of the key numbers:

The indicator amino acid data suggests that even untrained people need about 1.2 g/kg of protein per day, 50 percent more than the FDA鈥檚 recommended daily intake of 0.8 g/kg. And endurance athletes need another 50 percent more than untrained people, with a level of 1.8 g/k/g ensuring that 95 percent of people are getting all the protein their bodies can use. In comparison, using the same indicator amino acid method find that resistance-trained athletes need somewhere between 1.5 and 2.0 g/kg per day, raising the possibility that endurance athletes might actually need more protein than lifters.

There鈥檚 an important point to bear in mind, though: endurance athletes also tend to eat a lot more than the average person, which means they automatically get more protein. among American adults averages 1.25 g/kg for men and 1.09 g/kg for women, pretty close to the overall target of 1.2 g/kg for untrained people. In comparison, found that endurance athletes average 1.4 to 1.5 g/kg鈥攏ot quite at the 1.8 g/kg level, but not that far away.

There are some other nuances in that graph. Data on male-female differences is very sparse, but there are some hints that women might require more than men relative to their body weight. That might be particularly true during the luteal phase of the menstrual cycle, since progesterone can affect protein burning. Witard and his colleagues make a blanket recommendation that both male and female endurance athletes should aim for 1.8 g/kg, but they throw in the speculative possibility that females 鈥渕ay consider鈥� upping it to 1.9 g/kg during the luteal phase of their cycle.

Short-Term Protein Tactics

The big surprise in the data above is that endurance athletes seem to use more protein on their rest days than on training days. This finding has popped up in , and it鈥檚 definitely not what the scientists were expecting. It鈥檚 possible that there鈥檚 some quirk of metabolism that鈥檚 skewing the measurements used to assess protein needs when you try to compare exercise and non-exercise days.

But it鈥檚 also possible that the effect is real鈥攖hat when you give your body a break, its repair and adaptation mechanisms kick into overdrive and thus use more protein than usual. If this is true, it鈥檚 an argument for upping your protein intake on rest days: Witard and co. suggest aiming for 2.0 g/kg. And on a more fundamental level, it鈥檚 an argument for including true rest days in your training program periodically, since they seem to trigger recovery processes that don鈥檛 happen on normal training days. At this point, I鈥檇 say the jury is still out on whether the effect is real.

Either way, the researchers suggest aiming for 0.5 g/kg of protein following exercise to help repair any muscle damage incurred during the workout. For a 150-pound person, that鈥檚 34 grams of protein, which is what you鈥檇 get in a substantial meal with a good protein source. How soon is 鈥渁fter exercise鈥�? I don鈥檛 think there鈥檚 any convincing data that says it has to be immediately after. Your next meal is fine鈥攗nless your workout was after dinner and you鈥檙e planning to head to bed, in which case you should make a special effort to get some protein in.

The data also suggests that athletes use more protein when they鈥檙e training in a carbohydrate-depleted state. In this case, we鈥檙e not talking about a consistently low-carb diet, but rather doing certain training sessions in a low-carb state to help the body adapt to burning fat more efficiently. There鈥檚 decent evidence that protein can help power these workouts, and Witard suggests taking in 10 to 20 grams of protein before and/or during this type of session.

This idea of using protein to compensate for low carbs also connects to one of the most hotly debated ideas about protein for endurance athletes. There have been various research-backed claims over the years that adding protein to a sports drink that you consume during a race or training session will enhance your performance, and that taking in some protein in the immediate post-workout window will speed up the rate at which you refill the carbohydrate stores in your muscles.

All these claims, Witard and his colleagues argue, are the result of studies where the subjects didn鈥檛 get enough carbohydrates. If you鈥檙e meeting your carb needs, adding protein to a sports drink will neither boost your performance nor accelerate your muscle refueling. There may be exceptions for ultra-endurance events, which haven鈥檛 been well-studied and have somewhat different metabolic challenges compared to a marathon. But the researchers鈥� final conclusion is a reminder that for endurance athletes, despite protein鈥檚 current popularity, carbohydrate is still king.

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Failure is a big topic in the weight lifting world these days. When you鈥檙e doing an exercise, do you need to push each set to the point that you literally can鈥檛 complete one more rep? Old-school practical wisdom says yes. More recent scientific studies have suggested that training to failure isn鈥檛 necessary, and might actually be counterproductive because it takes such a big toll on both your muscles and your mind.

The truth is probably somewhere in the middle, according to a in Medicine & Science in Sports & Exercise鈥攂ut the results lean toward the idea that failure isn鈥檛 necessary for most of us. The study finds that getting close to failure produces strength gains that are similar to going all the way. That said, training to failure does build a little more muscle mass at some locations. The results of the study also offer some useful clues for those of us seeking the biggest muscle gains from the least amount of time and effort in the gym鈥攏ot because we鈥檙e lazy, I hasten to add, but because we want to spend that time and effort in other ways.

Brad Schoenfeld and his colleagues at City University of New York (CUNY) Lehman College put 42 participants鈥�34 men and 8 women鈥攖hrough an eight-week full-body training program. One group was assigned to complete all their sets to failure while the other was instructed to always stop short of failure. The volunteers were all experienced lifters who had been hitting the gym at least three times a week for more than a year, which means there were no easy gains to be had. And the experimental lifting protocol called for just two workouts a week, with each workout consisting of just one set of nine different exercises. In total, each workout took about half an hour.

This idea of short, single-set workouts isn鈥檛 radical or new. Back in the 1970s, Arthur Jones, the inventor of Nautilus exercise machines, an approach that relied exclusively on single sets to failure. The problem is that pushing to true failure is no joke. It takes a lot of mental focus, and it also takes more time to recover. If your primary interest is another sport like running, you don鈥檛 necessarily want your legs to feel like lead the day after a strength workout. So it would be nice if it were possible to get most of the benefits of a hard workout while stopping short of true failure.

To test that theory, the approach Schoenfeld and his colleagues used is called 鈥渞epetitions in reserve.鈥� The subjects in the non-failure group were instructed to continue each set until they felt they had two repetitions in reserve, meaning that they would be able to squeeze out two more complete reps before failing on the subsequent one. It seems like a much more humane way to train鈥攁nd it also turned out to be fairly effective.

The most surprising result of the study is that both groups got measurably bigger and stronger even though they were working out less often than they were before the study period. That fits with a bunch of previous research on the 鈥�minimum effective dose鈥� for strength training. It 诲辞别蝉苍鈥檛 mean that half an hour, twice a week is sufficient to maximize your gains. But it does mean that those of us for whom strength training is mostly a means to some other end (like staying healthy, avoiding injury, or being able to carry a heavy pack) can make progress with a relatively modest investment of time.

As far as the efficacy of training to failure goes, there were a whole bunch of different outcomes in the study. The simplest were one-rep max in the bench press and squat, as measures of upper and lower body strength. To test explosive power, the researchers used a countermovement jump (CMJ), which simply involves squatting down then leaping as high as possible in a single motion. To test muscular endurance, they had the subjects complete as many reps as possible (AMRAP) on a leg-extension machine lifting 60 percent of their body weight.

The four tests of strength (bench press, squat, CMJ, and AMRAP) are at the bottom. The solid vertical line at 0.0 corresponds to no change after eight weeks of training. Both bench press and squat increased, with no significant difference between groups. For example, max squat increased by 13.2 percent on average in the failure group and 12.4 percent in the reps-in-reserve group. Same with muscular endurance (AMRAP). Power (CMJ), on the other hand, increased more in the group that trained to failure.

The picture was different for muscle size, which is shown in the upper part of the graph above. Researchers used ultrasound to measure various points along the mid and lateral quadriceps (MQ and LQ on the graph) as well as the biceps and triceps. In most (but not all) cases, training to failure produced bigger gains in mass鈥攚hich might be ideal if you鈥檙e working out for aesthetic reasons, but not necessarily if you鈥檙e training for a weight-to-strength ratio sport like cycling or climbing.

There鈥檚 a key caveat here, which is that estimating reps in reserve is an inexact art. To check how inexact it was, the researchers sometimes asked their subjects to keep going after they鈥檇 estimated they had two reps left. The estimates were fairly good and got better over the course of the eight-week study. But these were experienced lifters who had presumably experienced true failure many times before. For newbies, , it鈥檚 probably a good idea to do at least some training to failure so that you know what it feels like. Then, once you have a good internal benchmark, switch to a reps-in-reserve approach.

In some ways, this line of research reminds me of the current debate in the endurance world about Norwegian double-threshold training. The underlying premise of the Norwegian method is that hero workouts that leave you crumpled by the side of the track are counterproductive. Better to push hard enough to stimulate adaptation but not so hard that you can鈥檛 recover for the next workout. Those who hope to win bodybuilding competitions will undoubtedly鈥攁nd wisely鈥攌eep lifting to failure. On the other hand, for those who want muscle and strength but care more deeply about tomorrow鈥檚 run, keeping a rep or two in reserve sounds like a great plan.

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Like all great villains, lactic acid has been misunderstood. We鈥檝e been blaming it for the pain we suffer during intense exercise for more than two centuries. There鈥檚 nothing worse, we say, than the 鈥渓actic burn鈥� that locks our failing muscles into immobility. More recent tellings of the story have tried to rehabilitate lactic acid鈥檚 reputation, insisting that it鈥檚 actually trying to fuel our muscles rather than shut them down. But that version 诲辞别蝉苍鈥檛 capture the full complexity, either.

Into this confusion steps , from veteran physiologists Simeon Cairns and Michael Lindinger. It鈥檚 a dense 35-page doorstop titled 鈥淟actic Acidosis: Implications for Human Exercise Performance,鈥� and the clearest conclusion we can draw from it is that the precise causes of muscle fatigue during intense exercise are still a topic of active research and vigorous debate among scientists. But the sudden popularity of baking soda as an acid-buffering performance aid has renewed conversations about how, exactly, lactic acid works in the body鈥攁nd how we might counteract it. Here are some highlights from the latest research.

The Lactic Backstory

The first scientist to draw the connection between exercise and lactic acid was J枚ns Jacob Berzelius, the Swedish chemist who devised the modern system of chemical notation (H2O and so on). Sometime around 1807, he noticed that the chopped-up muscles of dead deer contained lactic acid, a substance that had only recently been discovered in soured milk. Crucially, the muscles of stags that had been hunted to death contained higher levels of lactic acid, while deer from a slaughterhouse who had their limbs immobilized in a splint before their death had lower levels, suggesting that the acid was generated by physical exertion.

A century later, physiologists at the University of Cambridge used electric stimulation to make frogs鈥� legs twitch until they reached exhaustion, and high lactic acid levels. The levels were even higher if they performed the experiment in a chamber without oxygen, and lower if they provided extra oxygen. That finding helped establish the prevailing twentieth-century view: your muscles need oxygen to generate energy aerobically; if they can鈥檛 get enough oxygen, they switch to generating energy anaerobically, which produces lactic acid as a toxic byproduct that eventually shuts your muscles down.

There are two small problems鈥攁nd one big one鈥攚ith this picture. The first detail is that, while lactic acid can be measured in the muscles of dead deer and frogs, it 诲辞别蝉苍鈥檛 actually exist in living humans. In the chemical milieu of the body, what would be lactic acid is split into two components: lactate and hydrogen ions. That鈥檚 not just being persnickety about terminology: lactate and hydrogen ions behave differently than lactic acid would. In fact, they can have separate and sometimes even opposing effects.

The second detail is that lactate (and hydrogen ions) aren鈥檛 really produced because your muscles are 鈥渞unning out of oxygen.鈥� The chemical reactions that use oxygen to turn food into muscle fuel are efficient but slow, great for powering relatively easy and sustained exercise. But they can鈥檛 provide energy fast enough to supply an all-out sprint. For that, you鈥檒l eventually need to rely on lactate-producing anaerobic reactions, even if you鈥檙e huffing pure oxygen from a can.

The big problem with the old view of lactic acid is the idea that it’s a metabolic villain. It turns out that, far from being an inert byproduct, lactate can be recycled into fuel for your muscles. In fact, one of the key superpowers that well-trained athletes develop is the ability to reuse lactate more quickly. This rehabilitation of lactate鈥檚 reputation has been going on for now (though it still has ), but athletes are still left with an unanswered question: if lactate isn鈥檛 what causes muscle fatigue, what is?

What the New Review Reveals

The first thing that Cairns and Lindinger establish is that, yes, levels of lactate and hydrogen ions increase during intense exercise. This is most obvious during intense exercise lasting between about one and twenty minutes. Longer bouts of exercise are less intense, so they can be mostly fueled by non-lactate-producing aerobic energy, and bouts of exertion shorter than one minute simply don鈥檛 have time to produce much lactate.

The evidence is now clear that lactate itself 诲辞别蝉苍鈥檛 interfere in any significant way with muscle function. But lactate and hydrogen ions are produced simultaneously in exactly the same quantities during anaerobic exercise, which complicates the 鈥渓actic acid is a good guy after all鈥� narrative. Lactate may be great, but it comes with an equivalent helping of hydrogen ions鈥攁nd that may be a problem.

When you increase the concentration of hydrogen ions in a solution, you鈥檙e increasing its acidity. That鈥檚 how the pH scale is defined: it鈥檚 a measure of hydrogen ion concentration. During intense exercise, the pH in your fast-twitch muscle fibers (which seem to be particularly susceptible to hydrogen ion buildup) can drop from around 7.0 to 6.0. That change represents a ten-fold increase in the concentration of hydrogen ions鈥攁 situation that can wreak havoc on muscle contraction.

The idea that hydrogen ions are what cause muscle fatigue isn鈥檛 entirely straightforward either, though. When you start hard exercise, the concentration of hydrogen ions actually decreases for about 15 seconds while you use up another source of fast-acting muscle energy called phosphocreatine. And yet your muscles are already getting fatigued during this initial burst, losing some of their maximal force, while hydrogen ion levels are still lower than normal.

There鈥檚 also a disconnect when you stop exercising, or take a break between hard intervals. Hydrogen ion (and lactate) levels keep climbing for a few minutes, which is why the highest lactate levels are generally recorded several minutes after hard exercise. But you don鈥檛 get weaker after you stop exercising; you get stronger as you recover, despite the rising concentration of hydrogen ions. So hydrogen ions may play a role in muscle fatigue, but they can鈥檛 be the whole story.

Another possibility is that hydrogen ions may interact with other molecules to disrupt muscle contraction. The most prominent candidates are potassium and phosphate, both of which increase during exercise and are associated in some studies with muscle fatigue. What these and other candidates have in common is that there are a ton of conflicting results: they have different effects on muscle fibers depending on the level of acidity, the muscle temperature, and the test protocol. This suggests鈥攏ot surprisingly鈥攖hat there isn鈥檛 a single molecule that causes your muscles to lose their power. Instead, it鈥檚 the whole cocktail of things going on inside your muscles during hard exercise that matters.

What About the Burn?

Most of the research that Cairns and Lindinger describe deals with muscle properties: how quickly are your fibers losing their twitch force, and why? It鈥檚 true that, as a middle-distance runner, I鈥檝e sometimes staggered down the finishing straight of a race with the sense that my legs were literally ceasing to function. It鈥檚 an awful feeling to experience, but satisfying to look back on: you know you left nothing out there.

Far more common, though, is a softer limit. You feel a red-hot burn and spreading numbness in your legs, and you choose to back off a bit. This feeling that we used to describe as 鈥済oing lactic鈥� is significant in its own right. In interviews with athletes who鈥檝e begun using baking soda, a common theme is that they鈥檙e able to push harder for longer before feeling that burn in their legs, which in turn enables them to race faster.

One theory about the feeling of going lactic is that you鈥檙e literally starving your brain of oxygen. If you push hard enough, it鈥檚 not just your muscles that go more acidic; your whole bloodstream follows. Thanks to a phenomenon called the Bohr effect, rising acidity reduces the ability of your red blood cells to ferry oxygen from your lungs to the rest of your body, including your brain. In one study, all-out rowing caused oxygen saturation to drop from 97.5 to 89.0 percent, which is a big drop鈥攂ig enough, perhaps, to slow you down and contribute to the out-of-body feeling at the end of hard races.

We also have nerve sensors that keep the brain informed about the metabolic status of the muscles. These group III/IV afferents, as they鈥檙e known, keep tabs on the real-time levels of molecules like lactate and hydrogen ions. If you block these nerves with spinal injections of fentanyl, exercise feels great鈥攖oo great, in fact, because you鈥檒l lose all sense of pacing, go out too hard, then hit the wall.

The most telling finding about the lactic burn, in my view, was where they injected various molecules into the thumbs of volunteers in an attempt to reproduce that familiar feeling. Injecting lactate didn鈥檛 do it. Neither did injecting hydrogen ions, or ATP, a fuel molecule whose levels are also elevated during hard exercise. Injecting them in pairs didn鈥檛 do it either. But injecting all three at the levels you鈥檇 experience during moderate exercise produced a sensation of fatigue in their thumbs, even though they weren鈥檛 moving them. And injecting higher levels turned fatigue into pain.

That鈥檚 a distinction I try to keep in mind in the late stages of hard workouts, and at the crux of races. That burning feeling is real, and it鈥檚 associated with lactate and acidity and muscular fuel levels. But it鈥檚 just a feeling. The lactate and ATP are actually helping me. The hydrogen ions, in combination with various other metabolites accumulating in my muscles, not so much. They鈥檒l eventually stop me. But until they do, I can keep pushing.

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For a while, it really looked as though beet juice would beat the odds. Most hot new performance-boosting supplements, even if they claim to be backed by science, don鈥檛 hold up to scrutiny. But after making thanks to high-profile adherents like marathon star Paula Radcliffe, the first wave of high-quality studies supported the idea that beet juice really does improve endurance.

After a decade, though, the bloom had partly faded. There were concerns about its gastrointestinal effects (much as there were with baking soda, another popular endurance-booster), questions about the appropriate dosage, and rising suspicion that beet juice only worked in untrained or recreational athletes but not in serious competitors. These days I rarely hear runners talking about beet juice, and the flow of new studies has tailed off. But a new review takes a fresh look at the accumulated evidence, and concludes that we shouldn鈥檛 be too quick to dismiss the potential benefits of the juice.

Why Beet Juice Might Help

The key ingredient in beet juice, from an endurance perspective, is nitrate. Once you eat it, bacteria in your mouth convert nitrate to nitrite. Then the acidity in your stomach helps convert the nitrite to nitric oxide. Nitric oxide plays a whole bunch of roles in the body. That includes cueing your blood vessels to dilate, or widen, delivering more oxygen to the muscles, faster.

In 2007, Swedish researchers that consuming nitrate鈥攖hat nitric oxide precursor鈥攎akes exercise more efficient, enabling you to burn less oxygen while sustaining a given pace. Two years later, a team led by Andrew Jones at the University of Exeter that you could get a similar effect by drinking nitrate-rich beet juice.

In subsequent years, researchers tested the effects of beet juice on various types of exercise. Crucially, Jones鈥檚 group figured out how to strip the nitrate from beet juice to create an undetectable placebo, and found that athletes improved their performance when given regular beet juice but not nitrate-free beet juice. That made the claims much more convincing. Meanwhile, a company called began selling beet juice with standardized nitrate levels, and eventually added to make the doses more palatable.

When the International Olympic Committee put together on sports supplements in 2018, they included beet juice as one of just five performance-boosting supplements with solid evidence. (The others were caffeine, creatine, baking soda, and beta-alanine.)

What the New Review Found

Over the years, scientists have made numerous attempts to sum up the evidence for and against beet juice. The latest attempt, by a group led by Eric Tsz鈥慍hun Poon of the Chinese University of Hong Kong, is an 鈥渦mbrella review鈥� of nitrate supplementation, mostly from beet juice. It pools the results of 20 previous reviews that themselves aggregated the data from 180 individual studies with a total of 2,672 participants.

The problem with lumping that many studies together is that they measure outcomes differently, use different dosing protocols, and have different study populations. Still, the broad conclusion is that beet juice works鈥攁t least for some outcomes. Most significantly, it improves time to exhaustion: if you鈥檙e asked to run or cycle at a given pace for as long as you can, beet juice helps you go for longer.

On the other hand, there was no statistically significant benefit for time trials, where you cover a given distance as quickly as possible. That鈥檚 the type of competition we care about in the real world, so this non-result is concerning. Time-to-exhaustion tests produce much bigger changes than time trials: a common rule of thumb is that a 15 percent change in time to exhaustion corresponds to about one percent in a time trial. So it may simply be that the studies were too small to detect subtle improvements in time trial performance.

Check out the relative effect sizes for time to exhaustion and time trial in these forest plots. Each dot represents an individual study with its error bar; the farther to the right of the vertical line it is, the greater the performance boost nitrate provided.

Taking the time trial data at face value, the results still look pretty encouraging. They鈥檙e all positive; they just need more participants so that the error bars will get smaller and no longer overlap zero. Of course, eyeballing the data like that is risky because it allows us to draw whatever conclusions we want. But I find it difficult to imagine a scenario where improving your time to exhaustion 诲辞别蝉苍鈥檛 also translate into an advantage in time trials. The two tasks are different psychologically, but they both rely on the same underlying physiological toolset.

Poon and his colleagues also run some further analysis to check whether the dose makes a difference. They conclude that the effects are biggest when you take at least 6 mmoL (just under 400 milligrams) of nitrate per day, which happens to be almost exactly how much a single concentrated shot of beet juice contains. The effects are also maximized when you supplement for at least three consecutive days rather than just taking some on the day of a race.

What We Still Don鈥檛 Know

The big open question that Poon鈥檚 review 诲辞别蝉苍鈥檛 address is whether beet juice works in highly trained athletes. Several studies have found that the effect is either diminished or eliminated entirely in elite subjects. This isn鈥檛 surprising. Pretty much every intervention you can think of, including training itself, will have a smaller effect on people who are already well-trained. This ceiling effect is presumably because elite athletes have already optimized their physiology so thoroughly that there鈥檚 less room to improve.

The flip side of that coin is that, for elite athletes, even minuscule improvements can be the difference between victory and defeat. The size of a worthwhile improvement at the highest level is a fraction of a percent, which is all but impossible to reliably detect in typical sports science studies. For top athletes, the decision of whether or not to use beet juice will have to remain an educated guess for now.

There are other unanswered questions, like whether beet juice is better than consuming nitrate straight. There have been several studies suggesting that this is indeed the case. The theory is that other ingredients in beet juice, like polyphenols鈥攚hich function as antioxidants鈥攎ight act synergistically with nitrate to produce a bigger effect. But as pointed out last year, the evidence for this claim is too shaky to draw any reliable conclusions either way.

Probably the biggest risk in the beet juice data is the preponderance of small studies, some with fewer than ten subjects. It鈥檚 easy to get a fluke result with small sample sizes, and it鈥檚 human nature to get unduly excited about positive results鈥攚hich is why positive flukes often get published more often than negative flukes. So we should remain cautious about our level of certainty.

Despite that caveat, my overall impression is positive. I sent the following summary to Andy Jones, the scientist most associated with beet juice research, to see whether he would agree:

鈥淚t works. It probably works less well in elites, like most things, but there may still be an effect. Higher doses taken for at least a few days in a row probably increase your chances of a positive effect.鈥�

Jones thought that sounded reasonable. He pointed out that there鈥檚 a 听of evidence emerging that beet juice also enhances muscle strength and power in some circumstances, an effect that Poon鈥檚 review confirms. For endurance specifically, looking at the totality of evidence, Jones figures there鈥檚 a real effect. And he鈥檚 in good company. 鈥淓liud remains a big believer,鈥� he pointed out. That would be Eliud Kipchoge.

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Inflammation is a major buzzword these days鈥攁nd not just in the context of sprained ankles or itchy insect bites. Much of the discussion instead surrounds the chronic low-grade inflammation that tends to increase throughout your body as you age. This phenomenon is thought to contribute to a wide range of ills, like heart disease, cancer, and chronic pain. It even has a catchy name: 鈥渋nflammaging.鈥� Whether exercise helps or hinders this process has long been a topic of debate.

It鈥檚 clear that exercise causes a short-term surge of inflammation. One of the earliest in sports science, in 1901, tested blood samples from four competitors in the Boston Marathon. The results showed a spectacular surge of inflammatory markers after the race, which was, at the time, interpreted as worrisome evidence that 鈥渢he exercise had gone far beyond physiological limits.鈥�

In the years since then, we鈥檝e come to a more nuanced view of the links between exercise and inflammation. Yes, exercise triggers acute inflammation. But the body responds by deploying its own anti-inflammatory molecules. One theory is that the body鈥檚 defenses against inflammation then get stronger over time, so regular exercise actually protects you from inflammaging. Evidence for this claim is mixed, though, so researchers in Spain recently pooled the available data to investigate the effect of decades of serious athletic training on inflammation.

What鈥檚 the Problem with Inflammation?

Inflammation is a double-edged sword. It鈥檚 part of the body鈥檚 emergency response to stressors like an infection or a twisted ankle, a biochemical cascade that often results in swelling or soreness, but also calls in key molecules that initiate the defense and repair process. That鈥檚 why sports doctors use anti-inflammatory drugs more sparingly than they used to, because shutting down inflammation might delay recovery. In this context, inflammation is good鈥攁s long as it turns off again once the danger is past.

Inflammation becomes a problem when it鈥檚 chronic (meaning that it 诲辞别蝉苍鈥檛 shut off once a threat has been successfully dealt with) and systemic (meaning that it鈥檚 everywhere in the body rather than just at the site of an injury). Chronic inflammation is a characteristic鈥斺�攐f heart disease, cancer, diabetes, and various other conditions. To put it bluntly, if you have high levels of various inflammatory markers when you鈥檙e at rest, you鈥檙e likely to than someone with lower levels.

There are various reasons that you might have chronic inflammation: a lingering infection, high levels of psychological or emotional stress, and so on. Your diet can contribute, although there鈥檚 plenty of debate about which foods help or hinder (fiber, fruit, and vegetables are ; sugar and trans fats, not so much).

The big factor, though, is aging. As you get older, baseline levels of various inflammatory markers creep inexorably upward. It鈥檚 not entirely clear why it happens. is that dead or damaged cells accumulate and keep triggering the immune system at a low level; is that it鈥檚 caused by gradual changes in your gut microbiome. Whatever the cause, it鈥檚 bad news.

How Being an Athlete Affects Inflammaging

The new study, , comes from a joint research team led by I帽igo P茅rez鈥慍astillo of Abbott Nutrition in Spain, along with medical staff from the Real Madrid soccer club and the Real Madrid Graduate School, a sports-focused unit of the European University of Madrid. (Yes, that鈥檚 a real thing. .)

Previous research has shown that if you train for a few months, your baseline levels of inflammation will go down鈥攂ut then if you stop training, the levels go back up. What P茅rez鈥慍astillo wanted to know was whether, if you train at a reasonable level and simply never stop, you can avoid inflammaging altogether. To find out, he and his colleagues pooled the results of 17 studies with 649 participants in total, comparing lifelong masters athletes鈥攑eople over the age of 35 who train and compete regularly in a sport鈥攚ith healthy but untrained people both young and old.

One challenge with studying inflammation is that there鈥檚 no simple measure of it. Instead, there鈥檚 a whole collection of molecules that respond to various types of stimulus in various ways that increase or decrease inflammation. Some do both. Interleukin-6, for example, surges sharply and temporarily after exercise in a way that fights inflammation, but at higher levels during rest can promote inflammation.

This means you have to look holistically at a bunch of markers to get a sense of overall inflammation levels. When you do this, a fairly convincing pattern emerges in the data. If you compare masters athletes with age-matched peers who don鈥檛 train, the athletes have consistently lower levels of baseline inflammation. But if you compare them to young people in their 20s who don鈥檛 train, the young people have even lower levels. Youth trumps training, in this case.

The data isn鈥檛 totally uniform. The strongest results show up in comparisons of C-reactive protein, which is associated with inflammation, and interleukin-10, which fights inflammation. Older athletes have less of the former and more of the latter. Training didn鈥檛 seem to make any difference for tumor necrosis factor alpha, another inflammatory molecule.

For interleukin-6, the results were mixed. Training didn鈥檛 lower baseline levels by a statistically significant margin. But when you break out the data by sport, endurance training did have a significant benefit while resistance training didn鈥檛. That might be because endurance training has unique powers, or it might simply be that there haven鈥檛 been enough resistance training studies to see an effect. At this point, there鈥檚 no way of knowing.

If you were hoping for proof that running is the fountain of youth, you might see these results as a let-down. (I鈥檒l admit, I was hoping for better news.) It鈥檚 possible that we might eventually stop inflammaging entirely by pulling more levers: maybe it鈥檚 lifelong endurance training and eating some yet-to-be-determined mix of vegetables and fish and never raising your voice in anger. The more likely scenario, I suspect, is that nothing can halt the flow of time entirely. If that鈥檚 the case, then I鈥檒l take these results as a win.

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To predict your longevity, you have two main options. You can rely on the routine tests and measurements your doctor likes to order for you, such as blood pressure, cholesterol levels, weight, and so on. Or you can go down a biohacking rabbit hole the way tech millionaire turned did to live longer. Johnson鈥檚 obsessive self-measurement protocol involves tracking more than a hundred biomarkers, ranging from the telomere length in blood cells to the speed of his urine stream (which, at 25 milliliters per second, he reports, is in the 90th percentile of 40-year-olds).

Or perhaps there is a simpler option. The goal of self-measurement is to scrutinize which factors truly predict longevity, so that you can try to change them before it鈥檚 too late. A new study from biostatisticians at the University of Colorado, Johns Hopkins University, and several other institutions crunched data from the long-running National Health and Nutrition Examination Survey (NHANES), comparing the predictive power of 15 potential longevity markers. The winner鈥攁 better predictor than having diabetes or heart disease, receiving a cancer diagnosis, or even how old you are鈥攚as the amount of physical activity you perform in a typical day, as measured by a wrist tracker. Forget pee speed. The message to remember is: move or die.

How to Live Longer

It鈥檚 hardly revolutionary to suggest that exercise is good for you, of course. But the fact that people continue to latch on to ever more esoteric minutiae suggests that we continue to undersell its benefits. That might be a data problem, at least in part. It鈥檚 famously hard to quantify how much you move in a given day, and early epidemiological studies tended to rely on surveys in which people were asked to estimate how much they exercised. Later studies used cumbersome hip-mounted accelerometers that were seldom worn around the clock. The , published in Medicine and Science in Sports and Exercise, draws on NHANES data from subjects recruited between 2011 and 2014, the first wave of the study to employ convenient wrist-worn accelerometers that stay on all day and night.

Sure enough, it turns out that better data yields better predictions. The study zeroed in on 3,600 subjects between the ages of 50 and 80, and tracked them to see who died in the years following their baseline measurements. In addition to physical activity, the subjects were assessed for 14 of the best-known traditional risk factors for mortality: basic demographic information (age, gender, body mass index, race or ethnicity, educational level), lifestyle habits (alcohol consumption, smoking), preexisting medical conditions (diabetes, heart disease, congestive heart failure, stroke, cancer, mobility problems), and self-reported overall health. The best predictors for how to live longer? Physical activity, followed by age, mobility problems, self-assessed health, diabetes, and smoking. Take a moment to let that sink in: how much and how vigorously you move are more important than how old you are as a predictor of the years you鈥檝e got left.

These results don鈥檛 arrive out of nowhere. Back in 2016, the American Heart Association issued a scientific statement calling for cardiorespiratory fitness, which is what VO2 max tests measure, to be considered a vital sign that doctors assess during routine checkups. The accumulated evidence, according to the AHA, indicates that low VO2 max is a potentially stronger predictor of mortality than usual suspects like smoking, cholesterol, and high blood pressure. But there鈥檚 a key difference between the two data points: VO2 max is about 50 percent determined by your genes, whereas how much you move is more or less up to you.

Fitness Trackers Are Key to New Longevity Findings

All this suggests that the hype about wearable fitness trackers over the past decade or so might be justified. Wrist-worn accelerometers like Apple Watches, Fitbits, and Whoop bands, according to the new data, are tracking the single most powerful predictor of your future health. There鈥檚 a caveat, though, according to Erjia Cui, a University of Minnesota biostatistics professor and the joint lead author of the study. Consumer wearables generally spit out some sort of proprietary activity score instead of providing raw data, so it isn鈥檛 clear whether those activity scores have the same predictive value as Cui鈥檚 analysis. Still, the results suggest that tracking your total movement throughout the day, rather than just formal workouts, might be a powerful health check.

The inevitable question, then, is how much movement, and of what type, we need in order to live longer. What鈥檚 the target we should be aiming for? Cui and his colleagues track the raw acceleration data in increments of a hundredth of a second, which 诲辞别蝉苍鈥檛 translate very well to the screen of your smartwatch. The challenge remains about how to translate that flood of data into simple advice regarding how many minutes of daily exercise you need, how hard that exercise needs to be, and how much you should move around when not exercising.

To be honest, though, I鈥檓 not sure the quest to determine an exact formula for how much we should move is all that different from the belief that measuring your urine speed will give you actionable insights about your rate of aging. Metrics do matter, and keeping tabs on biomarkers backed by actual science, like blood pressure, makes sense. But it鈥檚 worth remembering that the measurement is not the object; the map is not the road. What鈥檚 exciting about Cui鈥檚 data is how it reshuffles our priorities, shifting the focus from all the little things our wearable tech now tracks to the one big thing that really works鈥攁nd which is also a worthwhile goal for its own sake. Want to live longer? Open the door, step outside, and get moving.

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The 2022 Tour de France Femmes was decided in the Vosges mountains, during a brutal seventh stage with three category-one climbs. Dutch rider Annemiek van Vleuten attacked on the second climb, then opened up a four-minute gap on the final push of the day, a grueling 3,163-foot ascent of the Grand Ballon. It was the hardest day of the Tour, and with another mountain stage coming the next day, recovery was crucial. But with their legs fried, their cortisol levels soaring, and their nervous systems cranked in fight-or-flight mode, would the riders actually be able to sleep properly?

Surprisingly, the answer was yes鈥攐r at least, mostly. Nine of the Women鈥檚 Tour riders were wearing Whoop bands on their wrists; their data, which was published earlier this year in Sports Medicine鈥擮pen, showed that the riders got an average of 7.6 hours of sleep that night, compared with an overall average of 7.7 hours both before and after the Tour. They did, however, spend a little more time than usual in light sleep and less in restorative REM sleep. Whether that matters in any practical sense is the fundamental question confronting athletes, coaches, and sports scientists as they enter a new era of sleep tracking. The technology is better than ever; we just have to figure out what to do with it.

Tracking Sleep Stages Is Still a Challenge

Sleep is hardly a new biohack, but it has been a hot topic in performance circles ever since neuroscientist Matthew Walker鈥檚 2017 book Why We Sleep. The problem with first-generation sleep trackers, though, was that they relied on accelerometers and basically assumed that if you weren鈥檛 moving, you were asleep. The latest generation of devices is more sophisticated, adding heart-rate measurements and other physiological cues like breathing rate and skin temperature to refine their algorithms, and able to tell the differences between distinct sleep stages. As a result, says Charli Sargent, a sleep scientist at Central Queensland University in Australia and lead author of the Tour de France study, 鈥淭he whole world is becoming a sleep laboratory.鈥�

Companies like Apple, Garmin, Oura, Polar, and Whoop have gotten very good at detecting sleep. Compared with sleep-lab studies, where subjects are wired up to record brain and muscle activity, the latest consumer wearables were typically 86 to 89 percent accurate at determining whether a wearer was asleep or awake, Sargent and her colleagues found. Detecting individual sleep stages, on the other hand, is still a work in progress: the wearables only got it right 50 to 61 percent of the time.

The picture for athletes is more complex. Many of the new sleep-stage algorithms rely on heart-rate variability, or HRV, the subtle fluctuations in timing from one beat to the next. HRV changes with sleep stage, but it鈥檚 also influenced by vigorous exercise. Indeed, Sargent found that HRV was systematically lower after mountain stages in male Tour de France riders. Another new study, led by Marc Poulin of the University of Calgary, had a group of healthy volunteers do a hard interval workout in the early evening, then tracked their sleep with an HRV-based Polar watch as well as collecting gold-standard sleep-lab data. The good news: the accuracy of the sleep tracker was undiminished by the workout.

What Can Athletes Do with the Data?

Overall, then, wearable sleep trackers are already pretty good, and they will likely continue to improve. The next question鈥攖he really hard one鈥攊s what we should do with the data. If cyclists are getting less REM sleep after mountain stages, what should they do differently? 鈥淩ide easier鈥� isn鈥檛 useful advice; and it hardly seems like we need a fancy algorithm to give us the usual sleep-hygiene advice about bedtimes, alcohol, and electronics before bed.

For some people, simply having objective data about when to hit the hay and when to wake up might function as a useful reminder to cover these bases, in the same way a step tracker spurs you to get your 10,000 steps. Athletes might also be interested in seeing how their sleep changes at altitude, as an indicator of whether they鈥檝e acclimatized and are ready for hard workouts. And there may eventually be subtler insights: for example, preliminary data from Poulin鈥檚 lab in older adults suggests that those who don鈥檛 get enough deep sleep are more likely to develop cognitive problems years later. For now, the best approach is to establish a baseline and then look for changes, Sargent says. If you usually get 15 to 20 percent deep sleep and that changes to 10 to 15 percent, you should probably figure out why.

Against these putative benefits, you have to weigh the risks. Poor sleep is not always a problem that can be solved by trying harder and worrying more about it鈥攐r by collecting sleep-tracking data. 鈥淎nxiety related to sleep can be both a symptom and a cause of some types of sleep problems,鈥� Sargent acknowledges. The study that sticks in my mind, from Oxford University in 2018, involved giving subjects bogus feedback about whether they鈥檇 slept well or poorly. Those who were told that they鈥檇 slept poorly the night before reported feeling scattered, fatigued, and cranky. A little bit of data can be a dangerous thing, especially if its accuracy is questionable.

As for the mystery behind the surprising finding that Tour cyclists sleep just fine, thank you very much, even after the physiological disruption of brutal mountain stages, Sargent and her colleagues propose a disarmingly simple explanation. The cyclists prioritized sleep: they went to bed early and consistently, and gave themselves plenty of time there; ergo, they slept well. Earlier studies found that super-intense endurance exercise, especially when repeated day after day, led to diminished sleep鈥攂ut the new generation of athletes are on top of it. There will be plenty to learn in years to come from the new sleep-measurement techniques, combined with robust analytical approaches like machine learning and AI. 鈥淚 consider sleep to be the next frontier in physiology,鈥� Poulin says. But none of it matters if you鈥檙e not putting in your time in the sack.

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