In 2018, I convinced myself my hormones were out of whack. Acne and unusual tiredness are supposedly tell-tale signs that your 鈥擨 had both. So, I scheduled an appointment with my physician and asked him to test my hormone levels.

A quick blood draw revealed that my androgens, a group of hormones produced by the adrenal gland and the ovaries in women and testicles in men (testosterone is the primary androgen), were elevated (and likely causing my skin to flare up).

My doctor聽said my hormones were imbalanced and prescribed me spironolactone, an anti-androgen medication that鈥檚 commonly prescribed to treat acne. He sent me on my way. But I hated the drug鈥攊t made me feel light-headed and dizzy. I later learned that if you have naturally low blood pressure, the drug could lead to faintness and dizziness.

So, after a follow-up convo with my doctor, I stopped taking it and started investigating natural ways to balance my hormones.

According to internet strangers, I could cure my hormonal imbalance by drinking spearmint tea and snacking on ginger. When I asked my doctor for his two cents, he told me this advice was bogus. And even though I was desperate for some type of natural cure that could level out my hormones, I knew鈥攄eep down鈥攖hese solutions were probably (read: definitely) too good to be true.

The experts I interviewed for this story summed up hormone balancing in a few words: a trend that claims you can perfect the amount of hormones in your body through holistic lifestyle changes like tweaking your diet or taking a supplement. 鈥淚t鈥檚 mostly pseudoscience,鈥� says , a gynecologist at Stanford Medicine. Here鈥檚 why attempting to balance your hormones with food is, frankly, complete nonsense.

What Does It Even Mean to 鈥淏alance Your Hormones鈥�?

It鈥檚 well-established that hormones play an important role in many , including sleep, energy levels, digestion, and mood. As such, if you have an imbalance鈥攚hich is officially diagnosed with a blood test鈥攎any aspects of your health can feel off.

People with thyroid abnormalities, for example, may feel too hot or too cold, constipated, or anxious and jittery. And those with polycystic ovarian syndrome (PCOS) may feel lethargic or sluggish.

Treatments for Hormonal Imbalances Have Long Been Scrutinized

Historically, doctors have hesitated to treat hormonal imbalances, says , a registered dietitian and associate professor in the Department of Nutritional Sciences at Texas Tech University. Years ago, certain hormone therapy (HT) treatments were linked to , causing many doctors to stop prescribing HT.

Over the years, has shown that HT can be incredibly , but many physicians, particularly those who are wary about potential side effects, are about prescribing it.

Furthermore, many hormone-related symptoms are poorly understood, tough to treat, or brushed off as psychosomatic by some physicians. So many people have felt gaslighted by their doctors when they complain of symptoms or, like me, don鈥檛 want to take a pharmaceutical drug with nasty side effects. 鈥淲hen doctors aren鈥檛 able to address an issue or when people feel dismissed, they go to other places for information or validation and treatment because they just want to feel better,鈥� says Voedisch.

Cue in: hormone balancing鈥攖he belief that by drinking, say, matcha or swallowing supplements like ashwagandha, you can naturally increase or decrease hormones such as cortisol and, consequently, get rid of whatever annoying symptoms you鈥檙e dealing with. The trend exploded because so many people have symptoms鈥攍ike fatigue, weight gain, sleep problems鈥攖hat they want to get rid of, regardless of whether or not they鈥檙e related to hormones.

It鈥檚 now marketed as a one-size-fits-all solution for anyone who鈥檚 ever felt a little off. 鈥淧eople are saying that everything that is wrong with a person comes down to the endocrine system,鈥� says , an associate professor in the sociology department at Rutgers University who studies hormone imbalances. (Spoiler: That鈥檚 not the case.)

The Hormone Balancing Trend Is Problematic for These Reasons

One of the main issues with hormone balancing is that many of the symptoms people are trying to correct鈥攚hether it be mood swings or cravings鈥攁re often due to factors that are totally unrelated to hormones. You may be stressed out, sleep-deprived, or eating poorly. Or you could have an underlying health issue, such as anxiety, arthritis, or insomnia, that you don鈥檛 want to overlook, as there are proven treatments that can help. 鈥淵ou need to make sure you鈥檙e also evaluating for other conditions鈥� before assuming your hormones are to blame, says Voedisch.

Even if it turns out your hormones are messed up, changing your diet probably won鈥檛 cure them.

You Can鈥檛 Balance Hormones with Food

As Childress told me, the endocrine system鈥攖he network of glands that regulate hormones鈥攈as a lot of physiological processes in place that automatically keep your hormones balanced. You鈥檇 have to eat extremely poorly (think: tons of processed foods, refined grains, and red meat) to override that sturdy system and cause your hormones to go haywire.

On the flip side, adding certain foods to your diet won鈥檛 magically fix a dysregulated endocrine system. Snacking on apples won鈥檛 improve your estrogen levels, says Voedisch, and eating more yams won鈥檛 fix your body鈥檚 progesterone production. The belief you can eat your way to A+ hormones? 鈥淭hat鈥檚 a myth,鈥� she says.

However, some hormonal imbalances can improve with a specialized diet鈥攂ut not in the way you鈥檇 think. Take PCOS, for example, which causes high testosterone, leading to too much insulin in your blood. When you consume fewer foods that cause insulin to spike, such as carbs and added sugars, you can counteract the health effects of excess testosterone, which include excess body hair and, over time, a higher risk of diabetes. 鈥淭hat鈥檒l bring down the insulin, which will help relieve some of the side effects of that disorder,鈥� says Childress. But even then鈥攜our diet can鈥檛 fix the testosterone problem, she adds.

The Majority of Hormone Balancing Content Is Targeted to Women

One of the biggest themes you鈥檒l find is that the bulk of hormone-balancing content is geared toward helping women look and feel better. Such regimens often promise clear skin, youth, endless energy, or slenderness. And they鈥檙e often promoted by thin, white women鈥攕trengthening this idea that you should be or look a certain way, says MacKendrick. 鈥淭hey鈥檙e not representing a range of different types of bodies or races,鈥� she says.

Most hormone-balancing content conveys a damaging and inaccurate message that when your hormones are in balance, you have the energy to be both a career woman and a mother and have a sex drive, according to MacKendrick.聽

This premise discounts the fact that female sex hormones, like estrogen and progesterone, are naturally erratic throughout a woman鈥檚 cycle鈥攖hey鈥檙e supposed to be. 鈥淭here鈥檚 no balancing that needs to happen there,鈥� says Voedisch. But hormone balancing capitalizes off a huge vulnerability鈥攖hat something about you is subpar, and you should try stabilizing your hormones to obtain this ideal physique. The messaging is much like the diet and anti-aging industries, says MacKendrick.

It鈥檚 Pseudoscience

Self-help books and influencers often claim that hormone balancing will relieve your fatigue or build muscle鈥攈ealth claims that are . 鈥淭he things these influencers are claiming are largely bogus,鈥� says Childress.

But if they鈥檙e B.S., why do so many people swear by hormone balancing? Well, they may just be eating healthier鈥攁nd when you add more nutrient-dense foods to your diet, workout regularly, and sleep better, your overall health improves. 鈥淚 think sometimes people may think they鈥檙e balancing their hormones, but they really just feel better because they鈥檙e eating better,鈥� says Childress.

Furthermore, there may be a potent placebo effect, which is a phenomenon that occurs when people鈥檚 health improves after taking a fake or ineffective treatment. You may notice that, after sipping on some hormone-balancing herbal tea for a few weeks, you feel stronger or more energetic for a bit鈥攂ut, eventually, that placebo effect will wear off, adds Voedisch.

Are the Claims That Hormone Balancing Improves Gut Health True? Maybe.

A 2021 review published in the journal suggests the gut microbiome, the community of live organisms that reside in the intestines, is influenced by sex hormones like estrogen, progesterone, and testosterone鈥攁nd vice versa.

For example, some researchers theorize that a poor diet聽may cause bacteria to leak out of your gut, circulate throughout your body, and activate your immune system, thereby causing a spike in insulin, which could cause the ovaries to release androgens. But that鈥檚 just a theory; there鈥檚 still a lot scientists don鈥檛 understand about the gut-hormone relationship. For now, it鈥檚 currently a stretch to say your eating habits can alter your sex hormones via your gut. 鈥淵our diet likely has very little to do with your sex hormones,鈥� says Childress.

Do This Instead of “Hormone Balancing”

Rather than experimenting with a new-age eating plan that promises to enhance your hormones, make an in-person appointment with a physician鈥攍ike an endocrinologist or gynecologist鈥攐r a registered dietitian who can look at your medical history, run diagnostic tests, and based on those results, develop a personalized care plan. They can discuss evidence-based treatments that can help you feel better.

If you do, in fact, have a thyroid disease, they can prescribe medications, such as thyroid replacement therapy, says Voedisch, and if you鈥檙e menopausal and have low estrogen, you can look into hormone replacement therapy.

And, hey鈥攊t鈥檚 always worth taking a look at what and how you eat. If you鈥檙e worried about your hormones, says Childress, it鈥檚 generally a good idea to load up on fruits and vegetables and cut out refined sugars (a la the Mediterranean diet). Prioritize your sleep, manage your stress, and get exercise. 鈥淭hese things matter just as much if not more than diet alone,鈥� she says. If you feel better, that鈥檚 great鈥攋ust know 鈥渋t may or may not have anything to do with your hormones,鈥� says Childress.

When I see a doctor or certified dietitian slinging a hormone-balancing regimen on TikTok, I want to believe they鈥檙e sharing sound medical advice. But you can鈥檛 snack your way to balanced hormones. As Voedisch told me, 鈥淚f someone is trying to sell you something your insurance won鈥檛 cover, and you have to pay out of pocket for it, I would be very suspicious.鈥�

Want more of聽国产吃瓜黑料鈥檚 Health stories?聽.

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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.

For more Sweat Science, join me on and , sign up for the , and check out my forthcoming book .

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In triathlon training, consistency is king. But what if that consistency was a culprit in your latest injury? As all too many of us know, like IT band syndrome, shin splints, and stress fractures often present themselves at the worst times and have been the bane of many great race preparations.

Consistent, repetitive motion with improper running form often causes these injuries. But according to new research out of the University of Florida, you probably don鈥檛 even know your form could use a tune-up 鈥� and your shoes might be the reason why.

The study, published in the journal ,聽consisted of 710 runners from various backgrounds. After asking each runner if they were a heel striker, non-heel striker (mid-foot or forefoot strike) or they 鈥渄idn鈥檛 know,鈥� the researchers examined each runner鈥檚 gait with a high-tech slow-mo motion capture system and analyzed their past running injuries.

The results were abundantly clear. Those runners who 鈥渄idn鈥檛 know鈥� their gait pattern had, by far, the greatest likelihood of sustaining a running-related injury.

The main contributing factor to runners not knowing their foot strike, or how their feet were hitting the ground, was the heel-to-toe drop of their training shoes. A higher drop, as well as higher shoe weight, led to less accurate body awareness and a higher likelihood of injury.

Additionally, those runners who changed their shoe type in the past six months were more likely to sustain a running-related injury.

So if shoes are part of the problem, is the solution simply changing them out? Yes and no. Let鈥檚 look at the takeaways and how can you apply them to reduce your risk of injury.

Shoe Choice Matters

As the study highlights, a shoes with high heel-to-toe drop and greater weight contribute to less awareness of foot strike. Opting for a shoe that has a lower drop and weight is an effective way to become more engaged (literally) with the ground and how your foot is interacting at the impact, loading, and takeoff stages of your run gait. A healthy foot will feel the ground, fully load, then utilize its 鈥渇ree鈥� stored energy to push you forward.

A more minimalistic shoe will let the foot function as it should. Further, a large heel-to-toe drop alters how the force of impact is distributed throughout the body. As shown in 聽on the effect of shoe drop on joint stress, a higher-drop results in much larger stress at the patellofemoral (knee) joint. Opting for a lower-drop shoe allows the body to distribute stress as it was designed to do, reducing excessive loading to individual joints.

Opting for trainers with a mild drop (4-6mm) and not too much 鈥渃lunk鈥� could be an easy way to become more aware of how you鈥檙e running and stay injury-free.

If you鈥檝e been running in a high heel-toe drop shoe and dealing with injury, it might be worth trying a different shoe. Just remember, as with any change, to progress gradually into your new shoes to allow the body time to adapt. Start with one to two runs per week, and slowly progress over four to five weeks until you can wear your new shoes full time.

Self-Awareness Matters More聽聽

Yes, the type of shoes you wear can be a culprit in running-related injury, especially if they blunt the signals your body needs for good running form. This study clearly shows that enhanced body awareness while running, particularly when it comes to foot strike, leads to lowered injury risk.

Becoming more cognizant of how your body is moving and how your foot interacts with the ground is a free way to decrease your risk of injury. Yes, it鈥檚 nice to listen to music or zone out with a podcast during a long run. However, it鈥檚 likely worth it to zone in to the task at hand now and then to ensure you鈥檙e moving well.

One helpful tip is to run in front of a mirror on a treadmill so you can watch yourself run in real time. It鈥檚 easy to adopt poor running mechanics without realizing it, especially when fatigue sets in. Unlike the friendly spectator yelling, 鈥淟ooking good!鈥� at mile 23 of the marathon, the mirror doesn鈥檛 lie.

The best part about working on your running form is that it will help you develop movement patterns that make you stronger instead of more likely to get injured. More importantly, it might even help you actually look good at mile 23!

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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.

For more Sweat Science, join me on and , sign up for the , and check out my forthcoming book .

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When , one of the first things she talked about in her post-race speech was period tracking.

鈥淔or this race, a lot of things were actually coming together,鈥� she said in her finish-line interview after the win. 鈥淪o for example, I was in the first half of my menstrual cycle, and I always told myself, once this happens on a world championship race day, this is the chance. I feel so much stronger than in the second [half].鈥�

It鈥檚 not the first time Philipp called out her menstrual cycle as a factor in her triathlon success. After setting an Ironman record of 8:18:20 at Hamburg in 2022, period tracking was a 鈥済ame changer鈥� in optimizing her training and nutrition.

Does this mean all triathletes with a period should track their menstrual cycles with the same attention to detail as power meter data, nutritional intake, and sleep? Could period tracking really help athletes crack the code for a PR?

If you spend any time on social media, you probably assume the answer is 鈥測es.鈥� Women鈥檚 health and performance 鈥� specifically, as it pertains to hormones, is a hot topic right now. There鈥檚 no shortage of influencers and self-proclaimed experts offering advice on how to use period tracking to optimize athletic performance, but actual credentialed experts proffering detailed advice and protocols? Those are harder to come by. That鈥檚 because the science of period tracking for athletic performance is in its infancy, says Dr. Kelly McNulty, sports physiology researcher at Northumbria University and founder of .

It鈥檚 great that we鈥檝e had this boom in menstrual cycle tracking,鈥� says McNulty. 鈥淢enstrual cycle tracking is more common now, and it鈥檚 advocated for, especially within elite environments, as something athletes should be doing. There鈥檚 a tendency that everyone鈥檚 a female health expert now, but on the flip side of that, the science isn鈥檛 quite there yet. We don鈥檛 want to be giving bad advice off low-quality research.鈥�

That鈥檚 not to say period tracking is a bad idea 鈥� only that athletes should beware of one-size-fits-all advice on how women perform during certain phases of the cycle. Let鈥檚 take a deeper look at how to make period tracking work for you, whether you鈥檙e just starting out in triathlon or an Ironman World Champion.

What the science says about period tracking for athletes

As Triathlete has written about before, . The major contributing factor to this dearth of information is a belief that it鈥檚 simply 鈥渢oo complicated鈥� to study women 鈥� their monthly menstrual cycle and resulting hormonal fluctuations skew otherwise straightforward results. The lack of research on this topic means data collected on males is extrapolated to females, and female athletes usually train based on recommendations made for male athletes.

McNulty was part of a 2021 research team that reviewed more than 5,000 studies across six popular sport and exercise journals, , with as few as 6% of studies focusing exclusively on females. 聽that even fewer studies looked at women by life stage 鈥� a particularly 鈥渋nvisible鈥� cohort is women going through midlife, perimenopause, and menopause. Simply put, the science on women isn鈥檛 that great, and though it is an area of increasing interest for researchers, McNulty says it will still be five to 10 years before there鈥檚 a robust body of high-quality research.

Still, McNulty warns, 鈥淓verybody鈥檚 an expert now. And so everyone鈥檚 coming out saying that they will tailor your training plan to your menstrual cycle, and it sounds too good to be true in a lot of ways. We don鈥檛 want to come in and tell people, 鈥楴o, this is a bad idea,鈥� but we do feel really strongly about making sure that people know that if you鈥檙e paying for someone to do that, and they鈥檙e claiming they鈥檙e an expert, that nobody鈥檚 really fully an expert on that, except for the people who are currently doing the research 鈥� and even they don鈥檛 have all the answers.鈥�

There are, of course, some already-published studies that indicate hormone fluctuations aren鈥檛 a complication; they鈥檙e actually key to understanding and optimizing athletic performance in women. Hormones like estrogen and progesterone rise and fall throughout a woman鈥檚 month-long menstrual cycle, influencing everything from how she performs in training or racing to how she recovers. have found hormones may affect ligament laxity, suggesting injury risk may increase at various stages of the cycle. There is also evidence that when hormones fluctuate, so too does a woman鈥檚 body鈥檚 ability to maintain proper hydration levels, metabolize nutrients, and regulate body temperature 鈥� unique factors critical to female athletic performance.

Should you avoid period-tracking apps for athletes?

These studies, plus a growing demand for women-specific health advice, have led to an influx of period-tracking apps for athletes, which help women monitor where they are in their monthly cycles. Some apps even recommend what kind of training to do (or avoid) and when.

Though such apps can be enlightening for female athletes looking for insights on their individual physiology, that there currently isn鈥檛 enough research to make standard recommendations related to period tracking and sport performance.

That doesn鈥檛 mean that period tracking is a waste of time; only that experts aren鈥檛 at the point to confidently say 鈥渙n X day of the cycle, women are best off doing Y workout and recovering with Z food.鈥� McNulty says the information period-tracking apps give is often generic, and given the variety in menstrual cycle experiences among women, the information presented might not always be suited to the specific athlete. Some with putting highly-sensitive health information into such apps.

While women wait for the scientific community to endorse a substantial body of evidence, there are still things athletes can do, McNulty says: 鈥滻f you are a female athlete or a coach/practitioner supporting a female athlete, then I recommend that you dive into the research and learn all you can about the potential effects hormones can have on women鈥檚 physiology. But do this with a critical eye.鈥�

McNulty also says women can develop their own 鈥渂espoke athlete guidelines,鈥� where each athlete uses her own expertise of her own body to identify patterns in performance. 鈥淲hen you learn more about your own menstrual cycle 鈥� what symptoms you experience and how you perform, train, and recover on certain days 鈥� you can use your knowledge and understanding to determine what bits of the research might apply to you and which don鈥檛. From there you can begin to tweak and adjust things to maximize or manage performance/training depending where you are in your cycle,鈥� she says.

It鈥檚 in these individual experiences of the menstrual cycle 鈥� not the advice of an app 鈥� where the biggest insights lie. 鈥淓very woman is different, and the research is only the beginning from which we can build our individualized content from,鈥� McNulty says. 鈥淏ut this only happens if we understand our bodies first.鈥�

How to track your period as an athlete

Tracking the menstrual cycle can be as simple as circling a day on a paper calendar or marking an X in your smartphone on the first day of your menstrual flow, or period. The menstrual cycle is counted from the first day of one period up to the first day of your next period.

The average menstrual cycle is 28 days long, but each woman is different. Some women鈥檚 periods are so regular that they can predict the day and time that the next one will start. Other women experience menstrual cycles that vary in length. Medically, periods are considered 鈥渞egular鈥� if they usually come every 24 to 38 days.

That menstrual cycle is further divided into four phases:

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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.

For more Sweat Science, join me on and , sign up for the , and check out my forthcoming book .

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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.

For more Sweat Science, join me on and , sign up for the , and check out my forthcoming book .

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One of the funny little details in Eliud Kipchoge鈥檚 attempts to run a sub-two-hour-marathon was the electric pace cars. In Nike鈥檚 Breaking2 race in 2017, they used a Tesla. In the INEOS 1:59 Challenge, where Kipchoge actually broke the barrier, it was an Audi e-tron equipped with a specially built cruise control that was accurate to within less than a meter over the entire marathon distance. 鈥淭here will be no emissions out of the back to upset any of the runners,鈥� one of the INEOS engineers .

Was this just window-dressing, like the strips of aerodynamic tape that the Breaking2 runners pasted to their calves? Or does a bit of exhaust in the air actually slow you down? over the years have attempted to answer this question, but the results have been unclear, in part because it鈥檚 difficult to get accurate readings of air quality on the racecourse itself. But a new study from a research team at Brown University, led by Elvira Fleury and Joseph Braun, offers a more definitive answer: it matters.

The Problem with Particulate Matter

Fleury and Braun used a 鈥渟patiotemporal machine learning model鈥� to produce detailed hyperlocal estimates of exactly how much fine particulate matter was in the air at each mile marker along the courses of nine major marathons in the U.S. for each year between 2003 and 2019. The model integrates readings from nearby air sensors with satellite data, weather, topography, and other inputs.

Fine particulate matter鈥攁lso known as PM2.5 or, more familiarly, soot鈥攔efers to particles that are less than 2.5 microns in diameter, and is produced by internal combustion engines, forest fires, and other sources. It鈥檚 easy to inhale, and can cross from your lungs into your bloodstream, triggering inflammation and oxidative damage that raises the risk of heart disease, diabetes, and other conditions. When you鈥檙e running, you breathe more air than usual, and suck it in through your mouth, which bypasses the nasal filtration (i.e. hairs) that would otherwise catch some of the particles. This triggers a variety of problems, including constricting the blood vessels that supply your muscles with oxygen鈥攂ad news for a marathoner.

The machine learning model showed that PM2.5 levels varied widely from place to place and year to year. Levels in Boston and Chicago were as high as 20 micrograms per cubic meter in some years, and as low as 2 or 3 micrograms per cubic meter in others. Other courses like New York, Houston, and Los Angeles were in a similar range. The study, , combined this pollution data with 2.5 million finishing times, adjusting for other factors like heat and humidity.

How Does Air Pollution Affect Marathoners?

Before digging into the results, it鈥檚 worth pausing to consider what we鈥檇 expect to see. On a superficial level, there are two big trends to consider. The obvious one is that slower runners are out there longer, so we鈥檇 expect the total amount of time lost to increase with finishing time. The other one is that faster runners tend to breathe more heavily, so they suck in more particles per breath and lodge them more deeply in their respiratory systems鈥攕o we might, conversely, expect the effects to decrease with finishing time.

The most important question, though, is whether there are any effects at all. Overall, male marathoners at a given percentile finishing position were 32 seconds slower for each increase of 1 microgram per cubic meter in PM2.5 levels; female marathoners were 25 seconds slower. That may sound like a modest effect, but it seemingly suggests that average Chicago Marathon times in a low-pollution year like 2019 (~3 micrograms per cubic meter), might be around eight minutes faster than in a high-pollution year like 2011 (~20 micrograms per cubic meter). Even if that turns out to be an overestimate鈥擨鈥檝e taken the most extreme comparison I could find鈥攊t suggests that we鈥檙e talking about minutes rather than milliseconds.

Here’s how the effect varied depending on finishing position. The graphs below show finishing percentile on the horizontal axis, with first place on the left and last place on the right. The change in finishing time per microgram per cubic meter of PM2.5 is on the vertical axis. Graph A shows male finishers, graph B shows female finishers.

In both cases, the pattern is roughly the same. The fastest finishers have a relatively small effect; the median (which for most of the races tends to be between 4:00 and 5:00) and slightly-faster-than-median finishers have the biggest effect; and the slowest finishers have a smaller effect.

What explains this curve? It鈥檚 hard to know. It could be competition between the two factors I mentioned above: shorter exposure time protects the faster finishers, less heavy breathing protects the slower finishers, but runners in the middle get hammered. There are also lots of other possibilities. Maybe more well-trained runners are less affected by breathing discomfort. Maybe the anti-inflammatory effects of high aerobic fitness confer some protection from the negative effects of pollution. Maybe you actually adapt to polluted air if you train in it enough. There are glimmers of evidence for all these effects, but they remain speculative.

What These Air Pollution Findings Mean in Practice

The idea that air pollution hurts athletic performance certainly isn鈥檛 new鈥攔ecall when U.S. athletes wore breathing masks to protect their lungs with they arrived in Beijing for the 2008 Olympics. What鈥檚 different here is that the effects are showing up even at very modest levels of air pollution. The for 24-hour exposure to PM2.5 is 35 micrograms per cubic meter, well above the levels seen in any of the races. The full-year standard was lowered last year from 12 to 9 micrograms per cubic meter. Of all the race-years analyzed, 61 percent of them were below this more rigid 9 micrograms per cubic meter standard鈥攁nd yet these pollution levels still impacted race times.

One takeaway, then, is that if you鈥檙e going for a big marathon PR and you have a private pace car guiding you, it might be worth going electric. More generally, add air quality to the long list of factors to consider in choosing a race or evaluating a performance after the fact. If you set your PR at Boston in 2004, or Chicago in 2011, or Philadelphia pretty much any year before 2015, your coulda-shoulda-woulda time just got a few minutes faster.

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In the summer of 1991, Mical Garcia was 19 years old, taking classes at a cosmetology school in the farm town of Manteca, California, when she got an alarming call from her stepdad in Las Vegas. Her mother had run off. He came home from work to find her possessions gone, and a note explaining that she鈥檇 been leading a double life and did not want to be contacted.

Mical, who helps people pronounce her name by saying 鈥渓ike 鈥榤e call you,鈥欌�� was surprised but not overly concerned at the time. Her mother, Linda Sue Anderson, was carefree and a bit wild. 鈥淲e鈥檇 play that song 鈥楧elta Dawn鈥� really loud, sing at the top of our lungs even though we didn鈥檛 have great voices, and dance,鈥� Mical told me recently. Her mom once took her to see the Vegas crooner Engelbert Humperdinck in concert. Linda was beautiful, always had her long blond hair done, her nails and makeup just so. 鈥淪he was never a Betty Crocker stay-at-home mom.鈥�

The flip side was mood swings, which Mical, who is now a nurse, thinks could have been diagnosed as bipolar disorder. Linda would lock herself in her room, leaving Mical to babysit her sister, Dulcenea, and her brother, Ethan, who everyone called Petey. 鈥淚 was in first or second grade, and I was cooking for them. My dad was traveling. She wouldn鈥檛 open the door.鈥� Other times Linda, who worked as a travel agent, would disappear for days.

The family moved around a lot. When their parents divorced, they were living near Lake Tahoe. Their father won full custody and took the family to Manteca. Linda remarried and settled in Nevada. Her new husband was a pit boss at Caesars Palace with a degree from Stanford University. 鈥淗e worshipped the ground she walked on,鈥� Mical said. 鈥淚 never heard they were having problems.鈥�

So when Linda ran off, the Garcia children figured she鈥檇 come back eventually鈥攋ust like she always had.

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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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