Wintertime Sadness

While most people assume that emotions start in your brain, and then spread into your body as physical feelings, cognitive science has long backed the opposite.  It’s called the attributive theory of emotion, and it posits that you first feel the bodily physical sensations, and then your brain notices, interprets, and labels those sensations as emotions.  In one famous study, subjects held pencils in their mouth in one of two different ways, which surreptitiously used the same muscles as either smiling or frowning. After just five minutes, the subjects rated themselves significantly happier or sadder, respectively, than just before they started with the pencil holds.

But many body feelings are fairly nebulous, and could match up with several different emotions.  So your brain also looks at context cues to try and figure out what you’re feeling, and why.  Fear, for example, is physiologically indistinguishable from excitement.  Which, in fact, is the basis for a great Cognitive Behavioral Therapy trick for dealing with anxiety or phobias: if you feel fear in your body (racing heart, sweaty palms, clenched stomach), but then consciously label that feeling as ‘excitement,’ the feeling matches the label well enough that your brain will play along.  So you’re not nervous about giving a speech – you’re excited to share your message.  You’re not afraid of flying – you’re extremely excited imagining how great the vacation is going to be when you land.  (Try it out – it works surprisingly well.)

Recently, I’ve been thinking about that in the context of Seasonal Affective Disorder, the wintertime blues that many people feel, especially in less sunny climes.  During the winter, people are often tired, slow, and low-energy; they want to stay indoors, huddled up in a blanket on the couch.  Because the physical feelings match, we call that feeling sad and depressed.  And so we treat the feeling, either with drugs, or with exposure to intense daylight-spectrum light and mega-dosing of vitamin D (the latter two of which are often as effective as the drugs, in case you want to Google those options up).

But over the past decades, we’ve increasingly realized that a lot of the ‘negative’ physical reactions your body produces actually serve positive purposes.  So if you get rid of those reactions, or substantially tamp them down, it often comes at a longer-term cost.  Consider inflammation – say, as a child’s fever, or in an athlete’s sore quads and hamstrings after a training run.  Sure, if a fever pitches dangerously high, meds to keep it down saves lives.  And if the athlete’s muscle soreness is bad enough to keep her up all night, the lost sleep may offset any upside from the training.  But, at slightly lower levels, that fever is actually helping the child’s body fight off the infection – something it would do less quickly and effectively if he’s given meds to drop his temperature back to normal.  And while a handful of Advil will make our runner feel better today, it will also interfere with the hormone signaling pathway needed to build muscle; in other words, those NSAIDs negate much of the point of going for the training run in the first place.

Human bodies fluctuate cyclically over a number of time periods, from our daily circadian rhythms, to our yearly circannual ones.  And many of the aspects of these cycles are still a mystery.  Though it takes up a third of our lifetimes, for example, we’re still not sure why people need to sleep, or what, exactly, it does for us.  Similarly, we know that there’s a swing over the course of the year – during the spring and summer, we have more energy, need less sleep, can more easily shed pounds of fat; whereas in the fall and winter, we bulk up, conserve energy, and want to curl up and sleep somewhere warm.  While a bunch of that likely stems from a basic evolutionary fact – it was harder to find sufficient calories in winter back in our hunter-gatherer days, so it made sense to hoard them during that time – I strongly suspect there are other physiological reasons for the swing.  Much as a field needs to lie fallow to recover between harvests, perhaps the winter slowdown allows for longer-term recovery in our bodies and brains, much as sleep allows at the daily level.

So, in short, I’m not sure ‘winter mode’ is something we want to cut out entirely, even if we have the tools to do so.  At the same, time I am also sure that calling that winter mode ‘sadness’ and ‘depression’ is a quick way to feel, well, sad and depressed.  So, take a page from the CBT book, and see if you can make that winter shift seem less terrible by smarter labeling.  I’m done with Seasonal Affective Disorder, and am instead referring to it – in my brain to myself, and in conversation with anyone else – as Happy Hibernation Mode.

Embrace the fact that being low-energy in the winter actually feels good – in other words, it’s nothing to be down about.  Happy hibernating!

It’s a Lie

This morning, I arrived at the gym feeling like crap.  Tired, sluggish, weak; mostly, I just wanted to go home and get back into bed.  Even carrying the empty bar felt hard.  As a friend used to joke, it seemed like a ‘heavy gravity day.’

Despite my own whiny objections, I buckled down, and starting lifting according to plan.  Lo and behold, I still felt like crap.  But I also managed to hit every one of my lifts.

In the bodybuilding world, a lot of gurus push the idea of “instinctive training” – crafting each day’s workout on the fly, based on what your body tells you it needs.  And, indeed, for some small set of experienced professional bodybuilders, that approach (plus a bucket-full of steroids) seems to work wonders.  For pretty much everyone else, it quickly devolves into blindly wandering the gym, randomly doing whatever exercise someone else happened to have just done nearby.

To be sure, there’s real value in listening to your body.  Don’t be stupid, and if something hurts, stop.  (Or, to quote the orthopedic advice of my old friend and famed physical therapist Kelly Starrett: “If it feels sketchy, it is sketchy.”)  But, for the most part, when people skip workouts, reduce the weight on a lift, or cut the speed or distance on a swim, bike, or run, it’s mostly because they just don’t feel like doing it.

That’s one of the best reasons to hire a good coach: with the distance of an outside perspective, it’s easier to craft workouts based on what’s beneficial, rather than on just what you’d like to do.  Even without a coach, you can simulate some of that yourself (as I do the roughly 50% of the time I write my own programming), by separating the planning and doing by at least several days in time; a week in advance, I’ll wisely assign myself something valuable but unpleasant that I’d otherwise never have chosen the day of.

But, however you get there, ideally, when a workout comes around, you should be able to turn off your brain, and power through.  Even if, like me this morning, you’re not sure you can pull it off.  In fact, you might be right.  But, more often, you’ll be surprised by how well things go once you get started.  As the great weightlifting coach John Broz once told me: “just pick up the weight, bro; how you feel is a lie.”

Process, Results

A few days ago, I ran into a friend at the gym. He’s an executive in his mid-50’s, a guy in good shape who takes fitness seriously. When I saw him, he had 315 pounds racked for a back squat. But, he told me, his knees had recently been acting up on heavy squat days. Could I watch the next set, he asked.

I did. And sure enough, my friend’s form was atrocious. Valgus knees and ankles, forward weight shift over his toes, depth about 1/4 to 1/3 of the way to parallel.

“That was a disaster,” I told him.

“Oh, I know,” he replied. “But if I squat with good form, I can’t lift nearly as much weight.”

He was willing to humor me for the sake of his knees, however, so we went back to the basics. Beginning with a 45 pound dumbbell goblet squat, drilling until it looked perfect. Then we went back to an empty barbell, until that looked perfect, too. And then we added weight, ten pounds at a time.

At 135 pounds, his squat looked great.
At 145, it was back to disaster.

“If you want to fix your knee issue,” I told him, “then squat with 135 pounds next time, and only add weight in subsequent sessions, no more than ten pounds from one session to the next, if your squat form still looks this pretty.”

At which point he balked.
“I can’t do that!” he exclaimed. “The guys here will think I can only squat 135 pounds.”
“And they’d be correct,” I told him. “That’s how much you can squat right.”

Still, I understood my friend’s concern. Six months ago, I tweaked my shoulder while bench pressing. For two weeks after, it hurt every time I lifted my arm above my head. And just when I thought it was getting better, concluded I could just power through, I benched again and tweaked it a second time.

So, taking my own medicine, I went back to ground zero. I worked face-pulls, bottom-up kettlebell presses, scapular drills, perfect bench press reps with just the empty bar. And then I slowly built back up, in ten-pound jumps, one workout to the next.

At the end of those six months, I’m now back to using more weight than I was before, and my shoulder feels great. But for the first few months, I dreaded seeing anyone I knew at the gym when I was building back up. Members and trainers I was friendly with would walk past, and I had a nearly irrepressible urge to explain, disclaim.

“Rehab,” I would tell them, gesturing sheepishly at my nearly empty bar.

It’s a hard impulse to fight, and one I see people struggle with all the time. Most people training in any gym are, first and foremost, trying to look cool while they’re training. But there’s a difference between developing a skill, and demonstrating it. Almost by definition, when you’re learning something new, or building strength or endurance, you make progress only when you’re right at your limit, out of your depth, looking terrible and incompetent, but challenging yourself enough to grow.

Which leads to a fundamental choice: you can either impress your buddies in< the gym with your performance, or you can impress the rest of the world later with your results. Put differently, you can look good while you’re working out, or you can look good from your working out.

So choose. Because, in my experience, you can’t really have both.

Type 1

Over the last decade, there's been a bunch of new research around the idea that type 1 diabetes might actually be caused by allergic reaction to food. In short, in certain genetically susceptible individuals, specific foods might be the trigger that kicks off the autoimmune attack on islet cells in the pancreas, the core of the disease.

While that's interesting for discovering ways to prevent new cases of type 1 diabetes in the future, given the very slow regeneration of pancreatic beta cells, researchers long assumed that it didn't really apply to people who are already diabetic. Once those cells were gone, they appeared to be gone for good.

However, a recent set of mouse studies, and a follow-up set of studies with human pancreas biopsies, has shown that intermittent use of the Fast Mimicking Diet led to substantial regeneration of beta cells, even in current type 1 diabetics.

It’s all still preliminary stuff, but it’s certainly suggestive of a route to a cure for current type 1 diabetics, and, even better, a safe and non-invasive one. If you or someone you know has type 1 diabetes, keep an eye on this research going forward.

[And, while we’re on the subject, if you or someone you know has type 2 (‘adult onset’) diabetes, the news is even better: we already know it can be reversed by lifestyle change.]

It’s the Shit

I get asked a lot of questions about gut bacteria these days, and for good reason; over the last decade, research on the importance of the intestinal microbiome for fitness and overall health has exploded.

Take, for example, one particularly persuasive study, which took fecal bacteria samples from pairs of identical twins in which one twin was lean and one was obese, and transplanted the samples into the intestines of germ-free mice. Lo and behold, the mice with transplanted microbiota from the lean twins stayed lean themselves, while the mice with obese twin microbiota quickly piled on weight.

Similar microbiota transplants between humans are already being used very successfully to fight deadly infections like C. difficile colitis, and are being researched for conditions ranging from multiple sclerosis to Parkinson’s disease.

Which leads to the obvious question: will poop transplants for weight loss be the next big fitness craze?

In short, I hope not. While I strongly suspect that managing our microbiome will be an important part of health in the decades to come, at the moment, we just don’t really know what we’re talking about. Clinical data is still scarce, and possible complications are immense. Even if getting microbiota from your skinniest friend did turn out to be a great diet plan, we still have no idea about all of the other effects of that same bacteria down the line.

And, based on historical record, there’s good reason to be concerned. In the 1950’s, for example, doctors began prescribing transplanted Human Growth Hormone to smaller children deficient in HGH. While the treatment proved effective for spurring growth, it wasn’t until decades later that hundreds of cases of the rare and fatal neurodegenerative Creutzfeldt–Jakob disease (colloquially “mad cow disease”) began to crop up in those HGH recipients. Scientists quickly discovered that prions (the cause of CJD) had inadvertently come along for the ride with the transplanted hormone.

So, in short, the microbiome is something we should be keeping an eye on.

And it probably would be wise to start doing the common-sense things that research has begun to show as likely to help your microbiome: eat a whole food diet, and include some pre-biotic (raw garlic, onions, etc.) and pro-biotic (pickled stuff, yogurt, etc.) foods; avoid unnecessary antibiotics; get a dog (seriously!); exercise; manage your stress.

But when it comes to more invasive ideas – whether fecal transplant or even just probiotic supplements (which are currently a bit of a wild west), I’d hold off for now. Whatever the short-term upsides, from my perspective, at least, the long-term unknown risks are just too great.


My parents are in their late 60s, but they remain in very good shape. They’re avid travelers, which regularly requires them to walk 10-15 miles in a day, with stairs and hills climbed, bags toted, etc.

Primarily, they’ve kept fit with ‘cardio’ workouts in their living room, using Leslie Sansone’s solid and much-loved Walk at Home DVDs (or, as my brother calls it, ‘frumping to the oldies.’)

However, recent research has made clear that also focusing on strength training is particularly important as we age. As one recent review paper put it:

Strength-training exercises have the ability to combat weakness and frailty and their debilitating consequences. Done regularly [it] builds muscle strength and muscle mass, and preserves bone density, independence, and vitality with age. In addition, strength training also has the ability to reduce the risk of osteoporosis and the signs and symptoms of numerous chronic diseases such as heart disease, arthritis, and type 2 diabetes, while also improving sleep and reducing depression.

In short, strength training is powerful stuff. And as further research has shown, those benefits are specific to lifting weights; it’s not sufficient to simply maintain a high level of physical activity in general.

So I suggested that my parents also consider hitting the gym once or twice a week. To which my mother replied that they do currently use dumbbells in those Sansone workouts. While that’s great, I clarified that she needed to go to the gym to focus on progressive overload. The health improvements of strength training come from consistently increasing the weight used over time; thus, if you’re using the same ten-pound dumbbells month after month, you’re no longer reaping the same benefits.

To illustrate, here’s an amazing pair of before and after MRI scans showing the increase in leg muscle mass after just twelve weeks of weight training, in a 92-year-old subject. (!!!)

If you want to live longer, healthier, then staying active (in a general, ‘use it or lose it’ sort of way) is hugely important. But adding in weight training, too, is an extremely powerful tool. And, as the scans show, it’s never too late to start.


Right now, the US is facing a terrible, relatively new problem: a surge in chronic disease.

One in two Americans suffers from chronic disease (more than half of those from multiple chronic conditions), which is responsible for more than seven out of every ten deaths annually. We spend more than $2.3 Trillion each year (about 12 percent of our GDP) treating chronic disease, and it’s likely only going to get worse going forward, as the rate of chronic disease in kids has more than doubled in the last twenty years.

Our healthcare system wasn’t built to deal with these kinds of chronic conditions. A century ago, our leading causes of death were acute, infectious disease (the top three: tuberculosis, typhoid, and pneumonia), and most other doctor visits were also for acute problems like appendicitis, gall bladder attacks, etc. For those kinds of issues, the medical system is incredibly effective: go see a doctor, get an antibiotic / have surgery, recover. And with new treatments and technologies coming online, we get better and better at acute treatment every year.

But that same system isn’t well-equipped to deal with chronic disease, where doctors’ current tools are largely focused on suppressing symptoms rather than dealing with underlying causes. If you have high cholesterol or high blood pressure, you can get a drug to take (for the rest of your life) to lower them, but rarely a serious look at why either is high in the first place.

Recent research suggests that more than 85% of chronic disease is caused by environmental factors, like diet, behavior (including movement / exercise), and lifestyle. Dealing with the root causes of those chronic diseases, then, involves helping patients build and sustain new patterns and habits over the long-haul.

Given the heavy load we already place on physicians, it’s not reasonable to expect them to accept responsibility for driving that kind of behavioral change, too. The average primary care provider has about 2500 patients on their roster, and sees each for visits lasting on average just 10-12 minutes. That’s enough time to diagnose symptoms, prescribe medication, and then follow up a few weeks later. But while most people will take a course of antibiotics their doctors prescribe, drastically fewer will make wholesale changes to their lifestyle, without substantial ongoing support.

Currently, the fitness industry is failing equally when it comes to providing that kind of support. Indeed, the vast majority of people who start a diet or join a gym today will be no better off (and often worse) a year from now, having seen little results, given up, and returned to their prior behavior. Roughly, the fitness world today is akin to where medicine was in 1850: a lot of new science is emerging, and a slew of potentially helpful tools and technologies are being developed, but it’s yet to coalesce into an effective standard of care.

Which, in short, is what Composite is really about. Our big, hairy, audacious goal is to bring the rigor of medicine into the world of fitness, to try and develop clinically-demonstrable effectiveness in treating the underlying causes of the majority of today’s chronic disease.

There are a number of other companies, too, living at the intersection of fitness, technology, and medicine, developing new best practices, to whom we look for ideas and inspiration. I strongly believe that, over the next twenty years, we’ll see a whole new fitness industry emerge from those kinds of companies, one that can work hand-in-hand with the existing medical system, to help the US address the problem of chronic disease. And I’m hoping that, with the right team, a bit of luck, and a lot hard work, Composite can help drive that change, can become a leader of that pack.

(Physical) Therapist’s Couch

The human body is pretty miraculous. It evolved to allow a nearly infinite number of movements: running, climbing, jumping, swinging, and more.

But you mostly use it for one thing: sitting down. You sit in your car or on the subway, you sit all day at your desk, you sit to eat lunch and dinner, and you sit on your couch to binge-watch Netflix at night.

That disjoint – between how your body was evolved to be used, and how you’re actually using it – causes all kinds of problems.

Here’s just one: when you sit, your hip flexors are in a shortened position. And after enough sitting, your body starts to treat that shortened position as the new normal. So when you stand back up, there’s not enough slack in the system. Your hip flexors are permanently tight.

That’s a problem by itself, since so many athletic movements – from running and jumping, to throwing a ball or throwing a punch – depend on generating powerful hip extension. Tight hip flexors oppose that extension, reducing the power you can create. It’s like driving with the parking brake on.

But the secondary effects are even worse. Let me explain:

Perhaps, in the past, you’ve bought beef to cook for dinner, and had to cut off the silver-skin.

Your muscles have silver-skin, too. It’s called fascia. In your body, your muscles cells are held together in bundles, and the fascia is what does the holding together.

In recent years, however, we’ve begun to realize that fascia also connects one bundle to the next, in running lines of tension. As the song says, your hip bone’s connected to your thigh bone. And, similarly, your hip muscle’s connected to your thigh muscle. Which, in turn, is connected to your calves, ankles and feet in one direction, and to your lower back, thoracic spine, shoulders and arms in the other.

In fact, there’s a single run of fascia that extends from your toes, up through your entire body, to your elbows. And your tight hip flexors are right in the middle of that fascia run.

When hip flexors get tight, they take slack out of the middle of the system, creating a game of ‘crack the whip’ that causes problems all the way up and down that chain. Now, your tight hip flexors start causing foot pain, or knee pain, or a bad back, or a tweaky shoulder.

Normalizing the length of your hip flexors, getting slack back in the system, has huge and far-reaching impacts.  It will make you a better athlete, prevent future injuries, and knock out a slew of nagging pains you’ve been living with too long.

Fortunately, you can make big inroads on fixing your hip flexors with just one simple stretch, popularized by Dr. Kelly Starrett. He calls it the ‘couch stretch’, because he and his family do it at night, on the front of their couch while they watch TV.

Here’s a demo, pulled from Composite’s 14-day Jump Start for new clients. (I cover similar topics as in this post for the first half of the video; if you just want to see the stretch, hop to about the six-minute mark.)

To recap:

  1. Get on your hands and knees in front of a wall (or, if you can’t peel yourself away from the tube, the arm of a couch).
  2. Put your right shin flat vertically against the wall; your knee should be wedged into the corner where the wall and floor meet, and your foot should be pointed so that your instep is against the wall.
  3. If you’re not bendy, this may be a stretch already. If you’re more flexible, you can put your left foot flat on the ground.
  4. Squeeze your butt. In particular, squeeze your right glute, the side with the foot that’s against the wall. This will help stabilize your low back, and correctly position your hips.
  5. While still squeezing your butt, try to lift your upper body upright. Think about making your spine long, extending the straight line between the top of your head and your tailbone. You want to get upright by opening at the hip, and not just by arching your low back.
  6. For bonus points, you can eventually work towards reaching both hands overhead, so long as you can do so with tight abs and glutes and with your back long and straight. In the beginning, however, you’ll probably want to use your hands on the floor or on your forward knee, to help push yourself upright. You can also put a box in front of your body, and push up on that.

Now hold that stretch for two minutes. (That’s how long it takes for the Golgi tendon organ receptors to give up, allowing you to reach your full stretch and make lasting change.) Then switch to the other side, and do two minutes on the other leg.

I strongly, strongly suggest timing yourself, as two minutes is waaaaaay longer than most people tend to hold a stretch by default otherwise. (Side note: interestingly, dentists similarly recommend toothbrushing for two minutes. There, too, without using a timer, most people average brushing for only a third of the recommended time. If you like having teeth, consider deploying your two-minute timer next to the sink while brushing, much as you do while Couch Stretching.)

The most common problems to guard against while doing the Couch Stretch:

  1. Your rear knee isn’t against the wall. Even if it means you can’t get your opposite foot up on the ground, keep your rear knee / shin / foot all the way up against the wall. That takes all the slack out of the system, making the stretch much more effective.
  2. Your forward foot is too close in. Take a big step forward with that foot, so that your forward shin is vertical, too.
  3. You’re over-arching your lower back. Hyper-extending your lumbar spine is a very common (and not very good for you) habit in general; it’s even more common in something like the couch stretch, where it’s easier to bend at your low back than to actually stretch the hip flexors you’re gunning for. Think about making your spine tall, and about keeping your low back flat, even if that means you can’t get as far towards upright.
  4. You’re making a ‘pain face’. Effective stretching isn’t a relaxing experience. Done right, the couch stretch is hard work! At the same time, it’s important not to grimace while doing it (more technically called ‘facial fixing’), which actually undercuts the neurological effectiveness of the stretch. Breathe, go to your happy place, and try to keep your face serene. It’s zen and the art of stretching!

That’s it.

Try it daily for the next two weeks; I suspect you’ll be pleasantly surprised by the huge positive impact.

Keep it Moving

If you’re an average, 180-pound person, all the capillaries in your body – the smallest blood vessels, where oxygen and other nutrients are exchanged with cells – can together hold about 3 gallons of blood.

But blood, like water, is heavy. So you evolved into a evolutionary compromise. Your body only contains about 1.5 gallons of blood at a time; much lighter to carry, but only half of what you need to provide for your whole body at once. Fortunately, your body also evolved a smart system of hemodynamics, a combination of forces that sends that blood to capillaries as it’s needed.

At the front end, your heart pushes oxygen- and nutrient-rich blood through your arteries.

Then the movement of your muscles pulls that blood from your arteries into your capillaries, to feed individual cells.

In other words, while your heart is circulating blood all the time, the oxygen and nutrients only make it to cells when the muscles around them are moving.

That’s one of the major problems with excessive sitting: without movement, your cells are starving.

But that’s just one problem. After 30 minutes of sitting, your metabolism slows down by 90%. A few hours in, you’ve got increased blood triglyceride and insulin levels, and reduced (good) HDL cholesterol and lipoprotein lipase (an enzyme that breaks down fat in your body).

So perhaps it shouldn’t be surprising that people who sit more are sicker and fatter than people who don’t.

What’s more, that’s independent of exercise. Even between people who work out for the same number of hours weekly, a greater number of hours spent sitting each day correlates with an increase in both body mass and all-causes mortality. Studies have tied sitting to huge increases in everything from type 2 diabetes to cardiovascular disease and cancer.

For example, excess daily sitting increases your risk of lung cancer even more than the second-hand-smoke effects of living with a smoker.

All of which is bad news, because we apparently really love to sit. The average desk worker spends 7-8 hours a day sitting at the office, then comes home to sit down for another 5 hours of daily TV.

Fortunately, the solution is simple: get up frequently and move around.

Research has shown that even short breaks (a couple of minutes) at low intensity (walking to the bathroom, or simply standing up) make a huge difference. One study showed that, the greater the number of breaks taken, the lower the waist circumference and BMI, and the better the blood lipids and glucose tolerance.

Of course, once you get into the flow of work, it’s easy to forget just how much you’re sitting. That’s why you need some gentle nudges:

First, several fitness trackers can provide regular reminders to move. You can make sure those alerts are set up on your Apple Watch (more info here), Jawbone (see “Idle Alerts” here) or Garmin Vivosmart (info on the “Move Alert” here).

Second, as most people carry a smart-phone at all times, a simple hourly chime app (like Chime for iPhone and Hourly Chime for Android) can be a suitable reminder. When you hear a ‘ding’, stand up for a minute or so. If you’re feeling saucy, you can set those apps for more frequent reminders – say, every 30 minutes. (These are particularly handy in the evening. If you’re watching TV, for example, you can keep watching, just stand up and move a bit for a minute or two while you do.)

Third, since people are most likely to sit for extended periods of time while working on their computers, it’s also worth adding in an even more insistent reminder on-screen. Breaktime for Mac or Rest for Windows will take over your screen at whatever interval your select, reminding you to stand up, shake it out, go the bathroom, grab a water or coffee, or similarly get that mini-dose of movement it takes to get your body back on track.

This one’s an even smaller habit than most – again, it just requires getting up and moving briefly throughout the day. But it’s also one of the most effective you can implement in your life.

Knock Your Socks Off

As I’ve written about before, the muscles in your feet are extremely important. When they’re engaged, your arch can absorb a huge amount of force, and the muscles further up the kinetic chain – in your legs and hips – work their best, too.

Whereas, when your arch collapses, every step smashes the small muscles and tendons in your feet. Worse, the navicular bone in your heel collapses inward, torquing your shin, and turning off muscles like your glute medius on the side of your hip. It’s a consistent cause of chronic pain in feet, knees, hips, and low-backs.

That’s why I’m a long-standing supporter of going barefoot: it allows you to use your feet (and, in turn, your legs) they way they’re meant to work.

Obviously, if you run along city streets (like I do here in NYC), you probably don’t want to go totally barefoot, should instead opt for some minimalist, zero-drop shoes. (I’m a big fan of Inov-8.) And if you’re working out in a commercial gym, even if you take off your shoes, you probably still want to keep on your socks, to avoid picking up infections like MRSA or ringworm from sweaty floors.

But when you’re padding around the house, you’re in the clear. And while you may already be taking off your shoes at the front door, there’s a big difference between going barefoot, and going sock-clad mostly barefoot.

First, though socks are more forgiving than shoes, they still squeeze your foot, preventing natural toe splay. Second, socks are slippery. Walking depends on friction – between your foot and the ground – to give you something to push against. Imagine walking on ice: with almost no friction between your shoes and the ground, you automatically start to take small, tentative, penguin-like steps, instead of natural human strides. Sure, socks on wood floor (or even carpet) aren’t nearly as slippery as shoes on ice. But they’re still slippery enough to change the way you walk, and to undercut the skill- and muscle-developing point of walking around barefoot in the first place.

So, in short, make a point to walk around your home without shoes – and without socks. It’s the healthiest thing to do.