In Booth’s analysis of all of this, there is a simple sentence that greatly adds to the urgency. We are not just talking about sick people or physical debilitation. He writes: “Sedentary lifestyle is associated with lower cognitive skills.” Stated more bluntly still, our inactivity is making us dumber. If anything, this conclusion can now be stated even more confidently, given the wealth of research in the decade since Booth made it. Both epidemiology and neuroscience have described the biochemistry that makes it so.
The definitive statement about this comes from a group of researchers headed by J. Eric Ahlskog from the Department of Neurology at the Mayo Clinic. Prompted by some inconclusive work by the National Institutes of Health, Ahlskog and his group undertook a comprehensive review of all the research they could find on the relationship between cognition and exercise. They used the keywords “cognition” and “exercise” to search the massive PubMed database of medical research. The search returned 1,603 published research papers on the topic, a number that in itself gives us some idea of how thoroughly this issue has been examined. And the researchers read every one of those papers and compiled conclusions in a paper of their own published in 2011.
Their emphasis was on dementia, in its severe form as Alzheimer’s disease but also as evidenced in problems like the memory loss and decline of mental acuity that we think of as a sign of aging. Their results are sweeping and speak to all of us, not just the elderly. First, the preponderance of those 1,603 studies showed that exercise delivered marked improvements for people suffering all the cognitive impairments examined, from minor memory loss to full-on Alzheimer’s. Further, the studies that examined middle-aged people who exercised regularly found a substantial preventive effect of all forms of impairment later in life. Exercise helps the afflicted but also prevents the affliction. Cognitive impairment is not so much a consequence of aging as it is a consequence of our sedentary lives.
Yet the consequences of dementia in our society are huge and getting much worse. A 2013 study by the Rand Corporation showed that now about 15 percent of people older than 71—3.8 million people—suffer from dementia. But the aging of baby boomers along with the way we live will nearly triple that number by 2040, to 9.1 million people. In addition, another 5.4 million people, 22 percent of those older than 71, suffer mild cognitive impairment, as opposed to full-on dementia. Current social costs of treating dementia alone in the United States are $109 billion, more than we spend treating either heart disease or cancer.
One might think the reason for this decline during old age is obvious. We have long thought that many of the late-life neurological problems of aging stem directly from the decline of the cardiovascular system, that poor circulation robs the brain of oxygen. The group at the Mayo Clinic did indeed follow this trail and did indeed find what they called a “vascular” effect. But interestingly, the weight of the evidence caused them to conclude this was secondary. The main benefit of exercise, they wrote, was improved neuroplasticity and neurogenesis. Specifically, they traced this to the key neurotrophic factors of exercise, the Miracle-Gro effect with BDNF that we have talked about, but also to a group of parallel biochemicals, especially IGF-1, or insulin-like growth factor.
To take this line of reasoning one step further, the researchers were able to find a number of papers in the pool that looked at brain growth—actual, physical, measurable brain growth—as a result of exercise and found that seniors who exercised developed “significantly larger hippocampal volumes,” and because the hippocampus participates in memory processing, they had improved memory as a result. They found that exercise also prevented a loss of gray matter overall (a loss common in aging) and, additionally, improved brain function as measured by functional magnetic resonance imaging, showing better and more robust connections throughout.
But now consider the word “aging,” which doesn’t just refer to old people. We are all aging, and as is the case with gravity on the rest of our bodies, the downward forces on our brains begin early and extend through life. This research is therefore relevant to all of life. We may well notice the loss of memory at age seventy-one, but it began a lot earlier. Which means there is every reason to start looking at this issue at the other end of life.
ALL EDUCATION IS PHYSICAL EDUCATION
There is an emerging and every-bit-as-robust body of research on the effects of exercise on young brains. Maybe the best example is not a research paper (although the project certainly has spawned its share of publications) but the long-running educational experiment that was the centerpiece of John Ratey’s book Spark. If you haven’t read the details of that case or the rest of the evidence presented in Spark, it’s worth doing so to see this issue unfold. But we can encapsulate it here by citing the experiment in the Naperville school district, which demonstrates unequivocally how exercise builds brains at the beginning of life. The Naperville school district became the national leader in recognizing this by integrating a comprehensive program of aerobic workouts into the daily routine for its students. The program has paid off handsomely in stunning improvements in academic performance, improvement at the level that would in and of itself benchmark the sort of education reform that the nation needs and never seems able to accomplish.
But as is the case with research on aging, the body of evidence regarding exercise has only grown since. To date, no one we know of has gone so far as to compile in meta-analysis all the research on exercise and young people, as was done with the Mayo Clinic study. Nonetheless, there are some large and compelling data sets that prove the point. One of our favorites is a result in California, where state officials looked at eight hundred thousand fifth-, seventh-, and ninth-grade students, ranking their performance on a series of six physical fitness standards against their scores on standardized math and language tests. The result was a clean, stair-stepped relationship: the more fitness standards a student met, the better the test scores.
Meanwhile, Sweden has assembled a massive database looking at 1.2 million boys who entered military service between 1950 and 1976, measuring both cardiovascular fitness and muscle strength against IQ and cognitive abilities when all the subjects were fifteen years old and again at eighteen. Cardiovascular fitness did indeed demonstrate the same positive relationship with both intellectual measurements. This study, however, went further and tracked the subjects into adulthood, finding that those with better fitness scores wound up with better education, more life satisfaction, and higher socioeconomic standing.
But there is an even more intriguing pattern in the Swedish case. The data set included 270,000 brothers and 1,300 identical twins and showed that cardio fitness and not familial relationship turned out to be the better predictor of both cognitive ability and IQ. That is, despite the popular assumption that IQ is genetically determined, fitness and not genes held the greater sway over these tests of intellect.
All of this traces to a thread of this idea that John has been following since the 1970s, when he first noticed that marathon runners suffered depression when they quit running. Stopping running was like stopping effective medication. This phenomenon goes beyond cognition to tie in the element of mental health.
Lately, and since John detailed these issues in Spark, there continues to be an ever-widening use of exercise in treating mental issues. We are seeing paper after paper showing positive results in treating anxiety, addictions, attention deficit disorder, obsessive-compulsive disorder, schizophrenia, and, lately, bipolar disorder, but nowhere has there been as much work done as with depression. In 2010, the American Psychiatric Association issued new guidelines for treating depression, and for the first time, exercise was listed as a proven treatment. Thus, the APA finally caught up with Hippocrates, who recommended that all people in a bad mood should go for a walk—and if it did not improve, walk again. The APA’s change of heart was fostered by a lot of this convincing new evidence.
Psychologist James Blumenthal of Duke University has been leading the charge. He conducted trials lookin
g at the effects of exercise on sedentary patients with anxiety or depression, and his research culminated in a seminal report in 1999. In this study, 156 sedentary depressed patients were assigned to one of three groups. One used increasing doses of sertraline, or Zoloft (a popular antidepressant), another began exercising three times a week for forty minutes each day, and the third received both the drug and the exercise regimen. At sixteen weeks there was no difference in their depression scores, but at the end of a ten-month follow-up, those still exercising were better off than those on pills alone.
Blumenthal was criticized by prominent psychopharmacologists for not having a placebo group, and so he completed another study, published in 2007, with 202 patients, showing similar positive results for those doing exercise. Since then there have been many other studies looking at both aerobic exercise and strength training, and both interventions show positive effects. Movement regimens such as yoga and tai chi also help, but not as much.
But looking at this impressive body of evidence—evidence largely absent in the public discussion of issues like education and health care—it’s easy enough to miss the most significant accomplishment of the research. The evidence begins with what we will call the epidemiological case, that is, a statistical examination of outcomes for people who exercise. This can take us only so far; it steers us toward the pitfall that scientists understand when they warn us that correlation is not cause. This is the very pitfall that allowed, say, tobacco companies to wriggle out of responsibility when early epidemiological studies showed that smoking was associated with lung cancer. But years later, science was able to delineate and prove the biochemical linkages that made this so. They described how smoking caused lung cancer, and now there is no doubt. Not many people have noticed, but we are well past that point now with brain health and exercise. Sedentary behavior causes brain impairment, and we know how: by depriving your brain of the flood of neurochemistry that evolution developed in order to grow brains and keep them healthy.
WILD MOTION
So we’ve made the case and now you see the next step coming, the directive to pay up the gym membership, squeeze into the Lycra, load yourself onto a treadmill or stationary bike six days a week, set the timer for thirty minutes, punch up the iPod workout playlist, and slog your way to health. You know the drill, but if you think this is it, then you haven’t been paying attention. The regimen described above is to movement what processed fast food is to a full-on feast. The gym drill may get you by—and we’re not against it—but this is about going wild, about getting better, being as good as you can be. There is a better way to move.
We hope to entice you out of the gym and, toward that end, invite you on a run with us, a late spring day of the sort that pulls you outdoors, the first day this year without gloves and a jacket, cold at first, but sun and a few hundred yards of warm-up make light dress just right. We’re in the Rocky Mountains. The path winds out from the trailhead through a short stretch of flat ground, a gentle warm-up, and then the climb begins, a short uphill that catches you pushing a bit too hard and then your clean, aerobic heart rate spikes past the red line. You hold your pace for as long as you can, pitting will against slope, and then you’re light-headed and winded and the quadriceps signal fatigue. Too soon for this. You’re busted, and you walk. Heart rate recovers as you climb, head clears in a few hundred yards, and then you notice the hill has flattened at ridgetop to deliver a sweeping vantage of the valley below. You take it in, recover, and now trot. You measure your pace, tune it to the incline, and then again you are running. You don’t let up but aim a steady climb for the first little summit you spot a hundred yards on. Now there’s mud, and the trail becomes a trench, catching the melt of a winter’s retreating snowdrift just above. More distress messages from quads and lungs, but you’ve got the pace right and hold it, light head be damned. And then you make that bit of a summit in a rush and a slight little giggle of triumph—first of the day—and then almost immediately sweep down the back side of the hill, shift gears, take it a bit too fast in skippy, quick steps, but it feels right, hopping rocks and roots, rocking off banked turns with a quick roll of the foot, vaulting puddles and little stubborn slicks of ice. The trail steepens and winds to a bend. You careen around the curve, bracing off rocks, and then spot a quick four-foot stair-step drop through a wall of rocks, step it, tick, tick, tick, splash in the mud below, then another bend and just beyond, the light signals the trail’s bend into tree cover, where sun does not penetrate this early in the year. Now you’re moving a bit too fast for control, and the next step places you on the high end of a foot-wide luge course of ice that ends in a bend above a rock-face cliff. Your feet look for grit and gravel of any kind, anything to slow your mad sliding scramble down. By all means do not panic now. Do not lock up and brake. Easy does it. Balance. Control. And just then your dog, who has been following you in all of this, decides, as she always does, that being behind you is not good enough, and she goes in for a quick pass on your cliff side by ducking between your feet, a canine foul of clipping. You get a half second to debate whether she goes over the cliff or you do, but then you notice you have bent one leg 90 degrees from the knee, just right, and the dog makes a quick move to expertly snake her way around your other leg, no foul. (Every animal knows way more than you do.) And you carry on, another grin, another little victory over the trail. And so on.
We’ve just given you a little slice of life, a description of maybe ten minutes of running on a mountain trail. In contrast, consider how we might describe ten minutes of running on a treadmill: Get on the treadmill, take a step, left foot, right foot. Repeat. Even the vicarious experience on the mountain trail, even reading along, invited more of your brain to come for the ride. With luck, our description of the mountain run engaged some of your mirror neurons, your sense of empathy. Even in the telling, it is information-rich and, as a result, engaging. So it is with the real thing.
This is not to say we are writing a prescription for mountain running as the single true and only heaven. Nonetheless, mountain running provides a great path to understanding an important element of productive exercise, and it may, in fact, be time to do away with the idea of an exercise routine. The term “exercise” is an artifact of our industrialized, regimented, domesticated lives. If the brain is to take full advantage of what we now understand about the importance of movement, then you don’t have to exercise; you’ve got to move. You’ve got to be nimble.
SMARTER MOVES
The argument that humans were born to run in many ways makes running the ideal subject to serve as a doorway into a better understanding of motion and brain development in general. Running lies at the core of the human experience, but that deep connection has also, in recent years, produced a flurry of investigation and research across disciplines that give this topic a better platform than most for launching the broader discussion of the importance of movement. This is especially true because the general line of thinking got a huge leg up into the popular discussion with the work of Christopher McDougall and his groundbreaking book, Born to Run, which encourages barefoot running on evolutionary grounds.
Ask any physical therapist who practices in a running town, and you’ll hear about McDougall’s influence. Such clinicians are fond of claiming a real affinity for his work, simply because barefoot running has delivered so many injuries and thus ensured a steady flow of income. Barefoot running is their business model. Press them further, though, as we have, and you will find out this is not so much a critique of McDougall’s work or the idea behind it. The injuries accrue from a narrow reading of that research, particularly the assumption that barefoot running is all about, well, bare feet. It’s not. But more tellingly, some physical therapists report that the injuries are accruing disproportionately to road runners, people who adopt minimalist shoes and then run serious mileage on consistent, flat, even terrain, the same surface and motion, step after step. Further, many people make the change too quickly and do not give their feet
time to overcome a lifetime of bad form. The resulting injuries, then, are not a contradiction of the whole idea; they are a confirmation.
The rationale behind minimalist or barefoot running is this: humans evolved without shoes but also evolved running. A lot of it, on the order of a 10K every day. This dictated a body and movement built around what is called a midfoot or forefoot strike. The foot does not reach out ahead of one’s body to land on its heel but, rather, tucks in under the body in a shorter, gentler stride. The long, heel-striking stride prevalent in competitive running became possible only with the introduction of heavily cushioned shoes. More important, that change in stride and shoes, while protecting the heel, shifted forces through ankles, knees, and hips, places not meant to take those forces, and as a consequence, runners become more, not less, injured in the long term—injuries that result from the shift in form allowed by artificially padded shoes.
This is an important principle that goes straight to the core and founding idea of this book: that shortsighted, simplistic, single-factor fixes—especially those that ignore the evolutionary design of our bodies—often create more problems than they solve. To some, this was the end of the story. Shoe companies, even the very ones that developed the heavily padded clunkers of the late twentieth century, got into the business of offering minimalist shoes: lightly padded, low-to-the-ground, slinky, lightweight bedroom slippers. Our culture, being what it is, thought this was the answer, that you fix a problem by buying a single product, be it shoe or pill, and people did buy them and made minimalist running shoes the fastest-growing category in the industry. And then many of these runners did nothing to change their running stride, but went straight out and started pounding pavement and treadmills and then lined up for physical therapists to fix a new set of problems. This is a cautionary tale for all of us, not just runners. A deeper reading of this idea is in order, and therein we might find some exquisite and marvelous detail to guide us through subjects beyond running.
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