On May 29, 1954鈥攋ust 23 days after Roger Bannister entered the history books as the world鈥檚 first sub-four-minute miler鈥攁 21-year-old British woman named Diane Leather notched a similar milestone. At the Midland Counties championship meet in Birmingham, she ran 4:59.6 to become the first woman under five minutes. 鈥淭hank goodness that鈥檚 over,鈥� . 鈥淣ow I can concentrate on my chemistry exams.鈥�

In the seven decades since then, women have edged steadily closer to Bannister鈥檚 mark. The current world record, set by Kenya鈥檚 three-time Olympic 1,500-meter champion Faith Kipyegon in 2023, is 4:07.64. Her corresponding 1,500-meter world record of 3:49.04 is equivalent to a mile in roughly 4:06.5, according to the . The gap is small enough, in other words, that you might start wondering just how fast she could go, and how close to the barrier she could get, in a rule-bending exhibition race modeled after Eliud Kipchoge鈥檚 sub-two-hour marathon events.

That鈥檚 the question 听颈苍 Royal Society Open Science by University of Colorado physiologist Rodger Kram, working with colleagues Edson Soares da Silva, Wouter Hoogkamer, and Shalaya Kipp. Their conclusion: start the countdown.

The Power of Drafting

Once you start bending rules, the tricky part is deciding when to stop. A downhill sub-four mile wouldn鈥檛 be particularly interesting, for example. In their analysis, Kram et al. focus on the potential role of hyper-optimized drafting鈥攔unning behind or between other runners to minimize the effects of aerodynamic drag. These same researchers have previously published research on drafting in marathoners (which I wrote about here), suggesting that getting the drafting right can save between three and five minutes for both elite and mid-pack marathoners.

Back in Bannister鈥檚 day, having pacemakers or 鈥渞abbits鈥� leading the race and blocking the wind for you was considered controversial. The current rules permit pacemakers as long as they start at the beginning of the race. You can鈥檛 have fresh rabbits hopping in at the halfway mark, which was the key rule broken in Kipchoge鈥檚 sub-two attempts. Bannister himself was paced by his training partners for more than 80 percent of the race. Kipyegon, in contrast, was paced just past the halfway mark, and even in the first half of the race she was too far behind her pacers to get the full aerodynamic benefits of their presence. That suggests there鈥檚 still scope for improvement.

Another factor in Kipyegon鈥檚 favor is her size: she鈥檚 reported as 5鈥� 2鈥�, a full foot shorter than Bannister was. You might think that air resistance should matter less to her, since she鈥檚 smaller. But smaller runners actually have to spend a greater proportion of their energy overcoming air resistance, because they have a greater ratio of surface area to volume. Kram and his colleagues calculate that when running at four-minute pace, air resistance takes 13.5 percent of Kipyegon鈥檚 energy compared to just 11.4 percent of Bannister鈥檚. That means she has more to gain from drafting.

How Kipyegon Could Break the Four-Minute-Mile Barrier

Kipyegon ran her mile record on a windless night in Monaco. She ran her first lap of 409.3 meters in 62.60 seconds, and the subsequent 400-meter laps in 62.00, 62.20, and 60.84 seconds. She was three to four meters behind the pacers for the first lap, 2.5 meters behind in the second lap, and 2 meters behind for the beginning of the third lap before the final pacer dropped out. Optimal (but practical) drafting, the researchers suggest, has the runners about 1.2 to 1.3 meters apart.

The key question is: how much of the energy 鈥渨asted鈥� on aerodynamic drag can you save by running close behind another runner? You can estimate this with wind tunnel experiments or computational fluid dynamics calculations, but the answers vary widely. Kram and his colleagues run the numbers with several representative values drawn from these studies.

The most conservative estimate is that you can reduce drag force by 39.5 percent at 1.3 meters behind the leader, with the savings decreasing as you drift farther back. The most optimistic one is that you can reduce it by as much as 75.6 percent with one pacer 1.2 meters ahead and a second one 1.2 meters behind you. Having a pacer behind you seems counterintuitive, but it helps keep air flowing smoothly past by minimizing the turbulence behind you.

You can use these values to estimate how fast Kipyegon would have run with exactly the same effort as her world record race but no drafting: between 4:10 and 4:12. You can also estimate what she would have run with no air resistance at all, for example on a treadmill: between 3:53 and 3:55.

And then you can plug in what she would have run with ideal pacers for the whole race. Using the more conservative 39.5 percent value for drafting effectiveness, you get a final time of 4:03.6. Using the optimistic 75.6 percent value, it鈥檚 3:59.37鈥攑retty much identical to Bannister鈥檚 3:59.4 back in 1954.

Back to Mile-Record Reality?

The calculations suggests that Kipyegon could dip under four only under the most perfect conditions. But how close to perfection can we get in the real world?

For drafting, there are two basic choices: male sub-four milers who pace the entire race, or two teams of female pacers who switch off halfway. Neither would be accepted for official records, and it鈥檚 not easy finding women who can run a half-mile in under 2:00 with an even, controlled pace. The researchers point out that the last two Olympic 800-meter champions, Athing Mu and Keely Hodgkinson, are both capable of running the pace, and happen to be unusually tall, which might increase their drafting effectiveness.

In Kipchoge鈥檚 marathons, they used an arrowhead formation with six pacers (in the first attempt) and a reverse arrowhead formation with seven pacers (in second attempt, which was successful). That鈥檚 nearly impossible to implement on a track, since the arrowhead extends to the right and left of the racer鈥攂ut Kram floats the idea of running at Franklin Field, the iconic home of the Penn Relays. Franklin鈥檚 lane four is 400 meters, meaning that Kipyegon could run in lane four with some of the arrowhead pacers in lanes three and five.

Kipchoge also benefited from hyper-optimized courses that minimized elevation changes and curves. You can鈥檛 make a track any flatter, but there may be ways of making it a few seconds faster. Geoff Burns, a biomechanist who works for the U.S. Olympic and Paralympic Committee, has a couple of great articles on the benefits of and . For a 400-meter track at four-minute-mile pace, Kram figures the optimal angle for banked corners would be 7 degrees around a curve with 36-meter radius.

Finally, you could take another page from Kipchoge鈥檚 playbook and push the envelope on shoe design. Current limit the thickness of spikes to 20 millimeters, but Kram figures a slightly thicker midsole might unlock some extra super-spike benefits.

There鈥檚 one other wrinkle to consider. The original data on Nike鈥檚 Vaporfly supershoes鈥攁 study co-authored by Hoogkamer, Kipp, and Kram, as it happens鈥攆ound that they improved running economy by four percent on average, but with individual results between 1.6 and 6.3 percent. Rumor has it that Kipchoge was on the high end of this range. Surprisingly, there seems to be a similar spread in the benefits of drafting. A study led by da Silva a few years ago found that a standardized drag force burned anywhere between 4.2 and 8.1 percent more energy in different individuals. We know that Kipyegon has once-in-a-generation running ability, but we don鈥檛 know how much she stands to benefit from drafting. A sub-four might require someone who鈥檚 off the charts in both.

All of this, of course, assumes that we believe the calculations on the benefits of drafting. The wide range of calculated values for drafting effectiveness is a sign that there鈥檚 still plenty of uncertainty about the exact numbers. Kipchoge鈥檚 sub-two marathon is generally thought to have been made possible by two key levers: supershoes and drafting. But as marathon world records have continued to fall even with suboptimal drafting, I鈥檝e begun to think that the shoes must be a bigger factor than the drafting. There鈥檚 really only one way to find out for sure, though: we need a Breaking4 Project.

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There鈥檚 tons of evidence, from hundreds of studies with hundreds of thousands of participants, showing that exercise is an effective tool to combat depression and other mental health issues like anxiety. These studies find that it鈥檚 at least as good as drugs or therapy, and perhaps . It鈥檚 now recommended in official guidelines around the world as a or treatment. Still, there鈥檚 an important caveat to consider: is all this evidence of a connection between exercise and mental health any good?

That鈥檚 the question debated in in Medicine & Science in Sports & Exercise, based on a symposium held at the annual meeting of the American College of Sports Medicine. Four researchers, led by Patrick O鈥機onnor of the University of Georgia, sift and weigh the various lines of evidence. Their conclusion is mixed: yes, there鈥檚 a relationship between exercise and mental health, but its real-world applicability isn鈥檛 as clear as you might think.

The Observational Evidence on Exercise and Mental Health

O鈥機onnor and his colleagues assess three main types of evidence. The first is observational studies, which measure levels of physical activity and mental health in large groups of people to see if they鈥檙e connected, and in some cases follow up over many years to see how those relationships evolve. The headline result here is pretty clear: people who are more physically active are less likely to suffer from depression and anxiety now and in the future.

Observational studies also suggest, albeit more weakly, that there鈥檚 a dose-response relationship between exercise and mental health: more is better. is enough to produce an effect, but higher amounts produce a bigger effect. It鈥檚 an open question, though, whether doing too much can actually hurt your mental health. Some studies, for example, have found links between overtraining in endurance athletes and symptoms of depression.

The big problem with observational studies is the question of causation. Are active people less likely to become depressed, or is it that people who are depressed are less likely to be active? To answer that, we need a different type of study.

The Evidence from Randomized Trials

The second line of evidence is from randomized control trials, or RCTs: tell one group of people to exercise, tell another group not to, and see if they fare differently. Overall, the evidence from RCTs lines up with the observational evidence: prescribing exercise improves or prevents the occurrence of depression and anxiety.

For example, here鈥檚 a graph from a 2024 meta-analysis of 218 RCTs with a total of over 14,000 participants, :

Dots that are farther to the left indicate how much a treatment aided depression compared to a control group. Notice that walking or jogging ranks slightly above cognitive behavioral therapy and far above SSRI drugs. That鈥檚 an encouraging picture.

The evidence still isn鈥檛 bulletproof, though. One problem is that it鈥檚 very difficult to avoid placebo effects. Participants who are randomized to exercise know that they鈥檙e exercising, and likely also know that it鈥檚 supposed to make them feel better. Conversely, those who sign up for an exercise-and-depression study and are assigned to not exercise will expect to get nothing from it. These expectations matter, especially when you鈥檙e looking at a difficult-to-measure outcome like mental health.

Another challenge is the timeframe. Exercise studies are time-consuming and expensive to run, so they seldom last more than six months. But a third of major depressive episodes spontaneously resolve within six months with no treatment, which is in part why FDA guidelines suggest that such trials should last two years, to ensure that results are real and durable.

Why Context Matters When Studying Exercise and Mental Health

The third and final body of evidence that O鈥機onnor and his colleagues dig into is the contextual details. Exercise itself seems to matter, they write, but 鈥渨ho we play with, whether we have fun, whether we are cheered or booed, and whether we leave the experience feeling proud and accepted, or shamed and rejected also matters.鈥�

For example, most of the research focuses on 鈥渓eisure time physical activity,鈥� meaning sports and fitness. But there are other types of physical activity: occupational (at work), transportation (active commuting), and domestic (chores around the house). Is there a difference between lifting weights in the gym and lifting lumber on a construction site? Between a walk in the park and a walk down the aisle of a warehouse?

One view of exercise鈥檚 brain benefits is that it鈥檚 all about neurotransmitters: getting the heart pumping produces endorphins and oxytocin and various other mood-altering chemicals. If that鈥檚 the case, then manual labor should be as powerful as sports, and working out alone in a dark basement should be just as good as meeting friends for a run on a sunny day. Both intuition and research suggest that this isn鈥檛 the case.

Instead, some of exercise鈥檚 apparent mental-health benefits are clearly contextual. Doing something that creates social connection and provides a feeling of accomplishment is probably helpful even if your heart rate doesn鈥檛 budge above its resting level. And conversely, an exercise program that leaves you feeling worse about yourself鈥攖hink of the clich茅 of old-school phys ed classes鈥攎ight not help your mental health regardless of how much it boosts your VO2 max.

This is where the big research gaps are, according to O鈥機onnor and his colleagues. It鈥檚 pretty clear at this point that exercise isn鈥檛 just correlated with mental health; it can change it. But the best ways to deploy it in the real world remains understudied. For now, the best advice is probably to follow your instincts. Don鈥檛 stress about what type of exercise you鈥檙e doing, how hard to push, or how long to go. For improving mental health, these variables seem to have surprisingly weak effects. Instead, focus on the big levers: whether you鈥檙e enjoying it, and whether you鈥檒l do it again tomorrow.

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Earlier this month, the Journal of Applied Physiology published a paper with the title 鈥淓vidence on Sex Differences in Sports Performance.鈥� Seems pretty straightforward, but of course it鈥檚 not. The gap between male and female athletes has become a major flashpoint in debates on whether transgender women and athletes with differences of sexual development, like the South African runner Caster Semenya, should be able to compete in women鈥檚 sports.

Three scientists鈥擬ichael Joyner of the Mayo Clinic, Sandra Hunter of the University of Michigan, and Jonathon Senefeld of the University of Illinois Urbana-Champaign鈥攑resent a series of seven statements on the topic of sex differences in sport, along with the evidence to support them. Some of them seem obvious, others less so. Whatever your opinion on the debate, I think it鈥檚 worth considering each of these statements (which I鈥檒l paraphrase) in turn, in order to understand what the current evidence says and where the gaps are. The full paper, including references, is free to read .

A note on terminology: the article deals with differences in sex rather than gender. Although it鈥檚 an oversimplification, I鈥檒l use the terms male and female to refer to people with XY and XX chromosomes, respectively.

1. Males outperform females in events that depend on strength, speed, power, and endurance.

The evidence cited here is primarily performance data from sports like running, jumping, and weightlifting, where outcomes are easily measured. Among elite adults, the male-female gap is typically above 10 percent. The largest gaps are seen in sports that depend on explosive power, like high jump and long jump, where the gap approaches 20 percent. Field sports are harder to measure, but to the extent that they involve running and jumping and lifting, similar conclusions should apply.

Are these gaps biologically determined, or, , the result of social factors like the limited opportunities for women in sport? Elite performance data, on its own, can鈥檛 answer this question. But there鈥檚 no question that the gap exists, and is nearly universal. There may be some exceptions in activities like , where the determinants of performance are more complex. Overall, though, this statement should be uncontroversial.

2. This male-female gap shows up before puberty.

This seems like a significant claim, because it suggests that males may have a performance advantage that isn鈥檛 erased even if a transgender woman has undergone hormone therapy to lower testosterone levels. The evidence, once again, is primarily from performance data. Take a look at this graph of age-group track and field results for boys and girls between 7 and 18 years old:

Between the ages of 7 and 9, boys seem to be ahead, on average, by 4 to 5 percent. The gap narrows between the ages of 10 and 12, presumably as girls start puberty earlier than boys. After the age of 13, male puberty gets going and the gap widens rapidly.

So what gives 8-year-old boys an edge? As Joyner and his colleagues acknowledge, it鈥檚 once again hard to distinguish between biological and social factors. There is a possible hormonal explanation. We undergo a 鈥渕inipuberty鈥� during the first few months of life, with a temporary increase in sex hormones that is associated with a subsequent increase in muscle and decrease in fat accumulation in boys. But it鈥檚 also true that boys tend to spend more time running and jumping in unstructured play, and this may reflect gendered social expectations rather than sex differences.

Overall, the small gap in pre-puberty performance doesn鈥檛 seem like strong evidence of ineradicable differences between males and females. Instead, it鈥檚 the subsequent shape of that curve that, as we鈥檒l see, turns out to be more significant.

3. The gap widens with puberty, along with changes in body structure and function.

In the graph above, male-female differences accelerate dramatically after the age of 13 and continue all the way to adulthood. Now it gets harder to attribute the changes to social factors, because there are a host of other changes that accompany puberty and are associated with sports performance: males see a greater increase in muscle, airway and lung size, heart size, oxygen-carrying capacity of the blood, and so on.

Perhaps the most obvious difference is height: by the age of 20, the average male is taller than 97 percent of women. Differences in lung size or hemoglobin levels are invisible to us; differences in muscle mass could conceivably be because boys are encouraged to work out more. But height? We see it all around us, and accept that it鈥檚 driven by biological sex differences.

4. The main driver of the male-female performance gap in adults is the surge in testosterone during male puberty.

Here鈥檚 when things get more contested. Where, you might ask, is the randomized controlled trial proving that males who go through puberty without testosterone are worse athletes, or that females who go through puberty with male levels of testosterone are better athletes? Such studies haven鈥檛 been done, for obvious practical and ethical reasons.

Joyner and his colleagues argue that we can instead piece together the evidence from studies showing links between testosterone levels and increased physical performance during puberty; the various studies in humans and animals showing testosterone鈥檚 effects on muscle, bone, and blood parameters; doping studies where volunteers took testosterone; and strong circumstantial hints like the graph above showing the widening performance gap during puberty. The evidence here isn鈥檛 perfect, but as a whole it鈥檚 convincing.

5. Body changes during female puberty can have negative effects on sports performance.

This is an angle I hadn鈥檛 thought much about. The discussion usually focuses on the advantages conferred on males by testosterone, but there are a distinct set of changes that females experience during puberty. For example, they accumulate more body fat; their growth plates fuse so they stop growing taller; they develop breasts, which can alter balance and movement patterns; their hips widen, which may increase injury risk; they experience hormonal fluctuations associated with the menstrual cycle that may (or may not!) affect performance; they may eventually miss training time during pregnancy and face increased injury risk when returning to training after childbirth.

There鈥檚 no doubt that all these changes occur, and that they have the potential to influence performance. Whether they collectively make a significant contribution to the gap between male and female athletic performance is less clear. It鈥檚 worth considering, but I鈥檇 classify it as an open question for now.

6. Suppressing male testosterone levels after puberty only partly eliminates the male-female performance gap.

There鈥檚 a smattering of case studies and comparison studies to support this statement. A 2023 U.S. Air Force in Military Medicine, for example, tracked fitness test scores for nearly 400 transgender servicemembers for up to four years after they began hormone therapy. For transgender women, performance on some tests, like the 1.5-mile run, ended up corresponding to average female times by the fourth year of hormone therapy. But for other tests like push-ups, there were still differences.

Here’s how push-up scores evolved in transgender women over the course of four years of hormone therapy. The red band shows the range of male scores within one standard deviation of average; the blue band shows the corresponding women鈥檚 range. Scores are still higher than average even after four years.

One reason for the retained advantage is that some of the changes that occur during puberty are irreversible. Those who go through male puberty will, on average, be taller and have bigger lungs. They鈥檒l lose muscle mass during hormone therapy, but still retain more than the female average. There鈥檚 also evidence for 鈥�muscle memory,鈥� a phenomenon that makes it easier to build muscle if you鈥檝e previously had it.

It’s worth noting that the significance of retained advantages will vary from sport to sport. Greater height and muscle mass matter a lot in sports like basketball and rugby; they may matter less in, say, marathon swimming.

7. Adding testosterone improves female performance, but doesn鈥檛 eliminate the male-female gap.

This claim is the mirror image of the previous one: transgender men improve various facets of sports performance after beginning hormone therapy, but they don鈥檛 gain the full ten percent. This supports the idea that testosterone matters for performance, but that timing also matters: it plays its most significant role during puberty.

These are the seven claims that Joyner and his co-authors make. Some are stronger than others. But even if you take them all at face value, they don鈥檛 tell you what the rules for transgender or intersex athletes should be. That involves a difficult balance between fairness and inclusion. Maybe the male-female differences discussed here are the most important consideration; maybe they鈥檙e outweighed by other factors. I don鈥檛 think there are any easy answers here, but any compromises we reach need to acknowledge that these differences exist and are persistent.

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Researchers in Germany recently published one of those studies that, now and then, make me question my core beliefs. I鈥檓 a supplement skeptic, but I try not to let that identity prevent me from assimilating new data. And if there鈥檚 one supplement whose possible benefits I鈥檝e been on the fence about in recent years, it鈥檚 vitamin D.

The new study, , is part of a major initiative to improve the performance of German elite athletes. A research team led by Sebastian Hacker of Justus Liebig University in Giessen studied 474 athletes on German national teams in a range of sports including hockey, table tennis, and three-on-three basketball. They tested vitamin D levels and measured (among other outcomes) handgrip strength.

Here’s the money shot:

This graph shows handgrip strength as a function of 25(OH)D levels, which is how vitamin D status is assessed in the blood.聽 The two dashed lines indicate the聽thresholds between聽vitamin D deficiency (below 20 ng/mL), insufficiency (between 20 and 30 ng/mL), and sufficiency聽(above 30 ng/mL). There have been long debates on where these thresholds should be set, but that鈥檚 the current thinking. Note that you鈥檒l sometimes see 25(OH)D levels expressed in nmol/L; to get to those units, multiply the values above by 2.5.

The key point: there鈥檚 a clear slope to the line. Higher levels of vitamin D are associated with stronger grip strength, which in turn has been associated with health, longevity, and (less clearly) athletic performance. For every 1 ng/mL increase in 25(OH)D, handgrip strength increases by 0.01 N/kg, which means that going from 20 to 30 ng/mL should boost your strength by about three percent.

The Case for Vitamin D Supplements as a Performance Aid

Vitamin D plays roles in a whole bunch of body systems, including bone health, immune function, and鈥攑erhaps most notably for athletes鈥攎uscle performance. If you鈥檙e truly deficient in vitamin D, there鈥檚 no doubt you should get your levels up. But the evidence in the 鈥渕erely insufficient鈥� range is less clear, even in this data. If you took all the values below 20 mg/mL out of the analysis, would there still be a relationship between vitamin and handgrip strength? It鈥檚 not clear.

This isn鈥檛 the first time researchers have shown a relationship between vitamin D and strength. In fact, pooled data from 28 studies with 5,700 participants and concluded that there鈥檚 a positive relationship between vitamin D levels and quadriceps strength. At least, that鈥檚 the headline result鈥攂ut when you look closer, it鈥檚 less convincing. The positive relationship was for quad strength when contracting the muscle at a specific speed of 180 degrees per second. But there was no relationship at a slower speed of 60 degrees per second. Worse still, there was a聽negative聽correlation for maximal contractions聽against an immoveable force: higher vitamin D levels were associated with smaller max force.

In other words, we shouldn鈥檛 be too quick to assume the new German data is definitive. Instead, it鈥檚 another data point in an ongoing debate. Another review, , finds 鈥渕ixed results鈥� in studies on the relationship between vitamin D levels and muscle mass and strength.

Causation or Correlation?

Even if we eventually conclude that there is a positive relationship between vitamin D levels and strength, it doesn鈥檛 necessarily follow that we should all start popping vitamin D pills. First of all, there鈥檚 the possibility of reverse causation. People who are strong and healthy may choose to spend more time exercising outdoors, which in turn may produce higher vitamin D levels. That鈥檚 actually one of the strengths of the new German study: since all the subjects were elite athletes, we can assume that they have similar levels of general fitness and physical activity.

There may also be confounding factors. Back in 2019, 国产吃瓜黑料 contributing editor Rowan Jacobsen wrote a surprising article in which he argued that the benefits of sunlight extend beyond merely raising vitamin D levels, most notably in triggering the release of nitric oxide from your skin into your bloodstream. If that鈥檚 the case, then taking vitamin D supplements won鈥檛 necessarily fix whatever problems are associated with lack of sunshine.

What we really want are intervention studies, where we give extra vitamin D to people and see if they get stronger. And we don鈥檛 want subjects who already have sufficient levels of vitamin D, because they stand to benefit less; instead we want people with insufficient levels. That鈥檚 what , this one from Estonia, did.

The Estonian researchers took 28 volunteers with 鈥渋nsufficient鈥� 25(OH)D levels in the low 20s mg/mL. Half of them got a placebo, and the other half took 8,000 IU per day of vitamin D, which eventually got their 25(OH)D levels up to a healthy 57 ng/mL. Both groups did 12 weeks of resistance training, but there were no discernible differences in their results, which were published in the journal Nutrients. Here are the gains in one-rep maximum for various exercises for the two groups:

In fact, the further you dig into the literature, the less convincing the data looks for vitamin D as an athletic supplement. For example, there was that found no significant benefit of vitamin D supplementation on muscle strength but a trend in the right direction. But even that weak finding was tainted by 鈥渒ey errors in the analytical approach,鈥� according to : the true effect is close to zero.

Of course, vitamin D鈥檚 merits as an athletic supplement are distinct from its potential for more general health purposes. Might it be that taking vitamin D supplements helps prevent cancer, heart disease, or type 2 diabetes; increases bone density; or reduces your risk of falls? No, no, no, no, and no, according to . More than 60 Mendelian randomization studies, which use genetic data to divide people into pseudo-randomized groups with high or low vitamin D levels, have generally found no difference in health outcomes.

Put it all together and the overall case for taking vitamin D supplements doesn鈥檛 look very compelling to me鈥攁ssuming, that is, that you don鈥檛 have a genuine deficiency. Defining that threshold is the tricky part. Is it below 20 ng/mL, which health authorities consider deficient? Is it below 30 ng/mL which they label insufficient? Is it somewhere higher or lower or in between? I鈥檓 not sure, so for now I鈥檒l hedge my bets: despite all my skepticism, I鈥檓 going to arrange to get my levels tested at my next doctor鈥檚 appointment.

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One of the big debates in endurance sports these days is about 鈥渢raining intensity distribution,鈥� which is a fancy term for how much of your training time you spend going easy, medium, or hard. The dominant paradigm is the polarized distribution, which calls for a lot of easy running, a little bit of hard running, and not much in the middle. But there are various other viewpoints, including the currently fashionable Norwegian training, which puts a heavy emphasis on medium efforts.

One way of exploring which training distribution is best is to look at the training diaries of the best endurance athletes in the world. That鈥檚 how the concept of polarized training was born, and it鈥檚 why Norwegian training is rising in popularity. Of course, this isn鈥檛 as reliable as a randomized trial. Maybe most elite athletes train in a certain way because it鈥檚 popular, not because it鈥檚 objectively better than the alternatives. And even if we figure out the best way for elites to train, it鈥檚 not clear that those insights will apply to the rest of us.

Another option to assess training intensity is to look at how the unwashed masses train: to sift through reams of data looking for the patterns and variables that predict the best race performances. That鈥檚 the approach taken in , from a group of researchers led by Daniel Muniz-Pumares of the University of Hertfordshire and Barry Smyth of University College Dublin. They analyzed 16 weeks of training data leading up to a marathon for 120,000 runners who recorded their training in Strava.

To Run Faster, Run More

Before delving into the nitty-gritty of training intensity distributions, we should start with the elephant in the training room. By far the best predictor of marathon time was how many miles a runner racked up. The researchers divided their sample into half-hour finishing groups: the fastest group was the sub-2:30 marathoners, the slowest group was those between 6:00 and 6:30.

On average, the runners accumulated 28 miles per week over the 16 weeks prior to their goal race. But there were big differences. Sub-2:30 runners ran 67 miles per week, about three times as much as those running slower than 4:30 and 60 percent more than even the sub-3:00 runners. Here鈥檚 the weekly mileage (in kilometers, on the vertical axis) as a function of marathon finishing time (in minutes, on the horizontal axis):

This is the men鈥檚 data; the women鈥檚 data show essentially the same pattern. The four different lines show the average mileage during four different four-week blocks before the race. There are some slight differences鈥攎ileage is highest five to eight weeks before the race, for example鈥攂ut the overall pattern is the same throughout: faster runners run more.

What the Training Intensity Distribution Reveals

You could be forgiven for thinking that this is painfully obvious. But what鈥檚 interesting is how the faster runners ran more. They didn鈥檛 just scale up their training proportionally compared to the slower runners. Instead, the difference was almost exclusively in how much easy running they did.

You can divide the accumulated training into three zones loosely corresponding to easy, threshold, and interval or race pace. (I won鈥檛 belabor the details of how they crunched the training data or defined the zone boundaries, but it鈥檚 based on calculating each runner鈥檚 critical speed using the approach I described in this article.)

When you break out the different training zones, you find that runners of all levels, from sub-2:30 all the way through 6:30 marathoners, did virtually identical amounts of hard zone 3 training. They also did very similar amounts of zone 2 threshold training. There鈥檚 a slight trend toward the faster runners doing a bit more, but it鈥檚 barely noticeable. All the variation鈥攔emember, there鈥檚 a threefold difference in total training volume鈥攊s packed into easy zone 1 running.

The graph below is a little busy (it once again breaks out the results into four-week blocks, even though the trends in each block are similar). The key point is that the red lines (zone 3) are flat, meaning that all the different pace groups accumulated similar amounts of hard running time. The orange lines (zone 2) are nearly flat. But the green lines curve sharply upward on the left side of the graph, showing that the faster runners do more easy running.

So It鈥檚 Polarized Training for the Win?

That depends on what you mean by 鈥減olarized.鈥� There鈥檚 a fairly convoluted debate (which I summed up here) on the meaning of the term, but there are two key elements. One is the idea that most of your running should be easy. That鈥檚 often summed up (as in the title of ) as 80-20 running: around 80 percent of your running should be easy, with the other 20 percent medium or hard. Muniz-Pumares鈥檚 new results support this view.

The second element is the idea that you should avoid medium intensities, since they鈥檙e too slow to give you the benefits of interval training but too hard to recover from if you鈥檙e trying to run big miles. That is where the name 鈥減olarized鈥� originally comes from, since most of your training is supposed to cluster at the extremes of easy or hard. But the new data doesn鈥檛 back this claim up: very few of the runners, whether fast or slow, were doing truly polarized training.

What the runners were doing instead is called pyramidal training. Classic polarized training might involve an 80:5:15 breakdown of easy, medium, and hard. Pyramidal training, instead, might be 80:15:5. Instead of avoiding the middle zone, you do a moderate amount. In practice, though, the distinction between polarized and pyramidal is hazier than it seems. Previous research has found that the exact same training plan might look either polarized or pyramidal depending on whether you calculate the intensity distribution using running speed, heart rate, or even the intended effort.

The bottom line, from my perspective, is that it鈥檚 not worth getting too wound up about the specific nomenclature. This data supports the idea of doing lots of easy running and modest amounts of medium or hard running. It doesn鈥檛 support the idea of avoiding the medium zone. Whether you call that polarized or pyramidal is up to you.

What鈥檚 Lost in Translation

As I noted at the top, this isn鈥檛 a randomized trial. We know that faster runners did more easy running than slower runners. We don鈥檛 know if doing more easy running would have turned the slower runners into faster runners. But even if it did, that assumes that the slower runners have the time or desire to run more鈥攁nd that鈥檚 by no means a safe bet.

The fundamental assumption for elites is that their training is primarily limited by what their bodies can handle. Polarized (or pyramidal) training is supposed to be effective because it鈥檚 an optimal way of racking up the greatest possible combination of training volume and intensity. To max out what your body can handle in a given week, aim for that 80-20 split.

Meanwhile, out in the real world, the key question isn鈥檛 how much my body can handle. It鈥檚 how much training I can squeeze in before work or between picking up the kids and making dinner or whatever. The 3:30 marathoners are putting in about four hours of training per week. It鈥檚 not hard to believe that adding an extra hour or two of easy running on top of what they鈥檙e already doing would make them faster.

The trickier鈥攂ut also more relevant鈥攓uestion is how to make them faster on four hours of training per week. Switching to an 80-20 split would actually mean doing less total mileage, because they would be replacing a big chunk of their medium or hard running with easy running. Sure, they would recover more quickly from each training session. But would they really end up going faster?

This is an open question, and I don鈥檛 think there鈥檚 any firm answer at this point. But my takeaway from all this is that we should think carefully about what constraints we鈥檙e imposing or accepting on our training. If time is really the issue, then spending more of that precious time running hard might make sense for you. But if 鈥淚 don鈥檛 have time鈥� is just another way of saying 鈥淚 don鈥檛 want to,鈥� or if you鈥檝e been held back by the fatigue and injuries that often accompany hard training, then it鈥檚 worth considering doing more easy running. It鈥檚 the easiest and least risky type of training鈥攁nd in this analysis, at least, it鈥檚 the one weird trick that distinguishes faster marathoners from slower ones.

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The more time you spend pursuing a skill, the better you get. So you can bet that an elite skier like 2023 Men鈥檚 Freeride World Tour Rider of the Year has spent a lot of time touring backcountry terrain. That experience has helped the athlete become both a champion skier and an expert at layering and packing for long days with variable conditions. He knows that if you鈥檙e not worried about being too cold, too warm, or too underprepared for remote exploring, you can focus on the things that really matter: technique, scenery, friends, and fun. From fuel and layers for the expedition to cozy slip-on shoes for post-tour comfort, here are some of the essentials Hitzig takes whenever he heads into the backcountry.

Safety and Navigation

Returning safely should always be priority number one. In addition to the critical avalanche safety equipment that every skier should carry when venturing beyond resort boundaries, Hitzig always packs a headlamp and carries his phone, which he uses to plan routes the night before a tour. The tools and tech are great, but, he emphasizes, 鈥渋t鈥檚 important to behave according to the conditions.鈥� Since many of his backcountry pursuits start at dawn and end at dusk, Hitzig is always sure to double-check his headlamp battery before setting out on his route: 鈥淯nexpected things happen in the backcountry鈥攜ou don鈥檛 want to be left in the dark.鈥� And no matter the intensity of your objective, you should always inform someone about your plans.

Skin and Eye Protection

Even on bluebird days, expect exposure to the cold and wind鈥攖here鈥檚 not much shelter from the elements above tree line. That鈥檚 why you need to go prepared with UV protection, goggles, and a neck gaiter to pull over your nose and mouth. Hitzig always protects exposed skin with sunscreen and uses a face covering. 鈥淚t takes time to find the right gaiter, but this is the safest and easiest way to protect your skin,鈥� he says. 鈥淚 also protect my eyes with good ski goggles and rarely take them off.鈥�

Hydration and Fuel

Your body needs fuel and hydration to perform in the backcountry. Skinning up steep terrain and being out in the cold is physically demanding, plus it requires a lot of calories and carbohydrates. That鈥檚 why Hitzig always packs a bottle of water and an energy drink. For food, he keeps it simple with something he enjoys like a sandwich and a sweet treat. And it鈥檚 not enough to pack water鈥攎ake sure you鈥檙e storing it in an insulated bottle. You don鈥檛 want to get caught in the mountains with a solid ice block and no water to drink.

Essential Layers

Base Layer: Xperior Merino 200

Comfort in the backcountry starts with your base layer. That鈥檚 why Hitzig puts his trust in the Xperior Merino 200, made with high-quality 100 percent merino wool. Merino is nature鈥檚 magic fabric, providing insulation while naturally wicking away moisture. This helps regulate your core body temperature during transitions and strenuous activity. Plus, merino naturally resists odor buildup and is soft on skin. 鈥淭he Xperior Merino 200 is very light, it keeps me super warm, and it鈥檚 comfortable,鈥� Hitzig says. 鈥淚f it gets too hot in the sun, you don鈥檛 start sweating immediately, which is what I really like about this long-sleeve.鈥� If you thought this base layer couldn鈥檛 get any better, it鈥檚 also made with renewable materials in an effort to help end plastic waste.

Midlayer: Xperior PrimaLoft Loose Fill Jacket聽

When the temperatures drop and the wind picks up, a lightweight insulated jacket becomes an essential for warmth (and safety). 鈥淭he is the perfect second layer for everyday adventures and backcountry tours,鈥� Hitzig says. 鈥淚f you need to shed a layer, this jacket packs up nice and small into its own pocket for easy storage.鈥� Even if a light rain or wintry mix picks up, the jacket has a water-repellent outer layer for uncompromised warmth in damp conditions, making it perfect for pursuits deep in the backcountry. A midlayer like this is a workhorse, getting pulled on and off countless times, so it鈥檚 made with durable 100 percent recycled nylon fabric designed to hold up in extreme elements.

Shell: Techrock C-Knit Jacket

Whether bombing a descent or skinning in a storm, Hitzig stays dry and warm in the . This reliable three-layer Gore-Tex shell does what it should, promising protection and comfort in the white room鈥攚here the jacket鈥檚 removable inner powder skirt becomes essential. Working hard in wet conditions? Pit vents and waterproof-breathable Gore-Tex C-Knit fabric help keep you moisture-free inside and out. 鈥淭his jacket is tough,鈥� Hitzig says. 鈥淎fter a long season with long days on the mountain, it shows hardly any signs of wear and tear, and the Gore-Tex ePE still keeps the water out.鈥� And like all the layers in Hitzig鈥檚 backcountry kit, his outer layer, made from 100 percent recycled nylon, makes no sacrifices in durability. This shell will work with you on every turn as you make your way back to civilization.

Apr猫s-Ski Comfort

Beacon off, car defrosting, warm drink in hand: It鈥檚 time for a footwear swap and an expedition recap with the crew. The Winter Slip-On Cold.Rdy is a sweet reward for the day鈥檚 efforts. Trading ski boots for comfy apr猫s shoes is something every backcountry skier looks forward to, including Hitzig. This shoe goes a couple levels better than most. It features ultragrippy tread for traveling wintry parking lots or walkways. And the cherry on top is the integrated heel step-down, so you can go from shoe to mule for max comfort and convenience at the end of every ski day.

is a global leader in the outdoor sporting goods industry. With the mission to enable all humans to live a more connected, conscious, and adventurous life, adidas Terrex combines high-performance technologies with fashion-forward designs to weather the forces of nature and inspire every human being to find their own summits.

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For the past decade or so, sports scientists have been obsessed with the benefits of heat training. The extra stress of heat triggers various adaptations that help you handle hot conditions, like more sweating. Some of these adaptations, like increased blood volume, may even give you a boost when competing in cooler conditions. As a result, many top athletes now incorporate elaborate heat protocols into their training.

What if the opposite is also true? At in Montreal last month, a physiologist named Dominique Gagnon presented new data suggesting that cold training might offer some unique metabolic benefits that translate into enhanced health and endurance performance. It鈥檚 just a hypothesis at this point, based on a decade鈥檚 worth of incremental research. But as we head into the darkest, coldest months of the year, it鈥檚 kind of nice to think that our winter training might pack an extra punch.

Gagnon is a Canadian who recently moved from Laurentian University, in northern Ontario, to Finland鈥檚 University of Jyv盲skyl盲, three hours north of Helsinki. He knows cold, in other words. At the annual Canadian Society for Exercise Physiology conference, he presented comparing the training effects of working out in either warm (77 degrees Fahrenheit) or cool (32 degrees) conditions. The goal was to figure out whether training in the cold would boost levels, which is one of the key adaptations that underlies aerobic fitness.

What鈥檚 So Great About Cold?

Gagnon鈥檚 research on exercise in the cold goes back over a decade. Back in 2013, for example, he published showing that cold-weather exercise relies on a different fuel mix than warmer conditions, burning more fat and less carbohydrate. He suspects that this is because when you鈥檙e exercising in comfortable temperatures, there鈥檚 actually some local overheating in the muscles themselves.

Human metabolism is only about 25 percent efficient鈥攃omparable to the internal combustion engine in your car鈥攕o three-quarters of the energy in your food is released as heat in the muscles. That means that the temperature inside your muscles can be high even when the rest of you is cool. The advantage of exercising in the cold, then, is that it prevents your muscle cells from overheating and enables them to keep burning more fat聽for aerobic energy, which relies on the mitochondria in your muscles. In the long run, that should boost mitochondria levels and train聽your body to become more efficient aerobically.

There are various other hints supporting this view. Researchers at the University of Nebraska at Omaha, for example, that exercise in the cold produced a bigger spike in the cellular signals that tell the body to produce more mitochondria, though the difference wasn鈥檛 statistically significant. And have shown that they get a bigger fitness boost from exercise when the air is mildly cold.

The New Findings on Cold Training

In Gagnon鈥檚 new study, 34 volunteers trained three times a week for seven weeks, doing interval workouts on an exercise bike. Before and after the training period, they had muscle biopsies, which involve removing a small chunk of muscle from the leg, in order to analyse how much mitochondria was present. Sure enough, the group that trained in 32-degree air had a significantly greater increase in several different markers of mitochondrial content. Gagnon is still analyzing the VO2 max data, but initial signs are that those training in the cold were more likely to see a significant increase.

Those are encouraging findings. But even if the results (which have not yet been peer-reviewed) hold up, the next big question is whether this approach is practical. How cold do you have to be? Gagnon鈥檚 subjects performed their cold training in the equivalent of shorts and a T-shirt, which is less than I would typically wear at that temperature, but not totally unreasonable. Would the effects be nullified if you wore a long-sleeve shirt and tights? Gagnon鈥檚 not sure yet鈥攂ut he emphasized that the goal isn鈥檛 to be cold, with measurably lower muscle and body temperature. Instead, it鈥檚 to avoid letting your muscles get too hot.

At this point, it鈥檚 worth flashing back to some findings I wrote about earlier this year. Stephen Cheung and his colleagues at Brock University in Canada showed that getting superficially cold, with no drop in core temperature, reduced time to exhaustion in a cycling test by about 30 percent. That involved sitting in a 32-degree room with a light breeze for half an hour before the subjects even started cycling. Staying in the room for longer, so that their core temperature actually dropped by a degree, reduced endurance by another 30 to 40 percent. This is not what Gagnon is aiming for.

Instead, the goal of cold training seems to be to let yourself get just cool enough that your muscles don鈥檛 overheat. Where that threshold is remains to be determined, and the results will need to be replicated before anyone takes them seriously. Gagnon is in discussions with the Finnish military, which has lots of personnel engaging in physical activity in perennially cold conditions, about further studies. Maybe it will turn out to be the next big thing in endurance training. Or maybe not. To be totally honest, I normally wouldn鈥檛 write about such preliminary results鈥攂ut the idea that it might be true will help get me through some cold training runs this winter.

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If you could patent and sell the idea of holding your breath before exercise to boost performance, it would be a bestseller. Not because it works, necessarily鈥攖he jury is still out on that. But because the logic is so good, the physiology is so fascinating, and the technique is so simple.

Instead, without a commercial imperative behind it, the idea has been floating around for years with no clear answers about whether it really works or not. Now , from a team led by Yiannis Christoulas of Aristotle University of Thessaloniki in Greece, offers the most encouraging sign yet that breath-holding might function as a legal form of do-it-yourself blood doping to temporarily enhance your endurance.

The idea is based on the mammalian diving reflex, which is the suite of physiological responses that automatically takes over when you dunk your head underwater. In a whole bunch of different ways, your body switches into oxygen-conserving mode to make sure you don鈥檛 run out while you鈥檙e submerged. For example, your heart rate slows down, and blood-flow to your extremities ramps down.

How Divers Get a Boost in Red Blood Cells

Most relevant here is that your spleen stores an extra reserve of oxygen-carrying red blood cells. When you dive, your spleen contracts, squeezing these extra red blood cells out into general circulation. This is the bit that is 鈥渟imilar to blood doping interventions,鈥� Christoulas and his colleagues explain: instead of giving yourself an IV with fresh red blood cells, you get them from your spleen. Previous experiments suggest that spleen contraction could boost hemoglobin levels and VO2 max by as much as 5 percent.

Nobody is suggesting that you should go freediving a few minutes before your next marathon. But you can elicit some aspects of the diving response simply by holding your breath; and you can ramp up the response by doing it with your face submerged in cold water. This is the idea that prompted by researchers in France suggesting apnea鈥攖hat is, breath-holding鈥攁s 鈥渁 new training method in sport.鈥�

Since then, there have been several attempts to harness the benefits of breath-holding for athletic gain, with different activities (swimming, cycling) and protocols (single breath-holds, repeated breath-holds, various recovery durations). Earlier this year, Jan Bourgois and his colleagues at Ghent University in Belgium an overview of these attempts in Experimental Physiology. The overall picture is that the physiology is real, but the practical effects seem to be too small to measure. Hard exercise makes your spleen contract anyway, so it may be that pre-contracting it with breath-holds doesn鈥檛 offer any additional benefit.

Dunking Your Face in Water May Be the Key to Breath Hold Success

Christoulas鈥檚 new study takes a different view, which is that previous studies haven鈥檛 gotten the protocol quite right. In particular, the failed studies have asked athletes to hold their breath, but haven鈥檛 dunked their faces in water, so they didn鈥檛 fully contract their spleens. The new study had 17 volunteers complete an incremental cycling test to exhaustion, lasting roughly ten minutes, with and without a series of five maximal breath-holds with face submerged in water at 50 degrees Fahrenheit. They took two minutes recovery between each breath-hold and then started the cycling test two minutes after the final hold.

The subjects were recreational athletes with no training in freediving or breath-holding. Their average breath-hold time was 71 seconds鈥攖hough it鈥檚 interesting to note that the duration of each successive hold got longer. The first hold averaged just over 40 seconds; the second one was over 60 seconds; the last couple averaged close to 80 seconds. Here are the average breath-hold times (BHT), plus and minus standard deviations, for the five holds:

This progression is partly a result of the spleen鈥檚 extra red blood cells in action. Sure enough, blood tests showed that hemoglobin and red blood cell count were both up by 4 percent by the end of the last breath-hold.

The key performance result was that the subjects lasted, on average, 0.75 percent longer in the cycling test after the breath-holds, which was a small but statistically significant difference. It also took longer before they hit the second ventilatory threshold, which is the point when your breathing gets really labored.

It鈥檚 More than Just Red Blood Cells Increasing Subjects鈥� Endurance

It鈥檚 worth noting that there are several other mechanisms that might play a role in addition to spleen contraction. Breath-holding raises levels of carbon dioxide in the blood, which in turn (through a mechanism called ) makes it easier for your muscles to unload oxygen from circulating red blood cells. This boosts your aerobic metabolism, and helps explain why the blood tests also showed that resting lactate levels dropped by 15 percent after the breath-holds. The full physiological picture gets quite complicated, but the bottom line is that the subjects in the new study had better鈥�slightly 产别迟迟别谤鈥攅苍诲耻谤补苍肠别.

What does this mean in practice? Personally, I can鈥檛 imagine completing a set of five maximal breath-holds two minutes before a race. But some researchers have suggested that a single hold should be enough to get most of the benefits. If you look back at that graph of breath-hold times, it does appear that the biggest change occurs after the first bout, and there are fewer changes after the second one. Maybe two breath-holds a few minutes before competition is feasible.

The other big question is whether a good, hard warm-up accomplishes the same thing. In the new study, all subjects did a ten-minute warm-up that included jogging and 鈥渄ynamic whole-body stretches.鈥� But it鈥檚 possible that a longer and harder warm-up might trigger spleen contraction on its own. These are questions that future studies will have to answer鈥攁nd I hope they do, one way or the other, because it鈥檚 refreshing to consider a weird and wonderful source of potential 鈥渕arginal gains鈥� that, for a change, is free for everyone.

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Shaun White has been the face of snowboarding for two decades. So what is he doing in retirement? A lot. He鈥檚 launching his own snowboard brand. He鈥檚 raising money to protect public lands. He鈥檚 even starting his own half-pipe competition. In this live interview from The 国产吃瓜黑料 Festival in Denver, former NFL linebacker Dhani Jones talks with White about life after pro sports and how the keys to his past success play a role in his future.

Tickets to the 2025 国产吃瓜黑料 Festival and Summit are on sale now at early bird prices at

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