The Revolutionary New Science of Exercise and the Brain
John Ratey
Exercise is the single most powerful tool for optimizing brain function — here is the science.
Physical activity literally grows new brain cells. Ratey presents decades of neuroscience showing that exercise elevates mood, combats anxiety, sharpens attention, and protects against cognitive decline — effects no medication can fully replicate.
Everything Ratey wants you to walk away with
A Duke University study showed exercise outperformed sertraline for depression. Exercise has a profound impact on cognitive abilities and mental health. It is simply one of the best treatments for most psychiatric problems.
Exercise elevates serotonin, norepinephrine, and dopamine — the same neurotransmitters targeted by antidepressants and ADHD medications. But unlike drugs, exercise balances the entire system rather than adjusting one chemical in isolation.
Brain-derived neurotrophic factor builds and maintains cell circuitry. When sprinkled on neurons in a petri dish, cells sprouted new branches. German researchers found people learn vocabulary 20% faster after exercise, with the rate correlating directly to BDNF levels.
Students who exercised before class improved reading comprehension by 17%. Exercise spawns new neurons in the hippocampus from stem cells. The body was designed to be pushed — and in pushing our bodies, we push our brains too.
You can't learn complex material during high-intensity exercise because blood shunts away from the prefrontal cortex. But immediately after, your brain is primed for sharp thinking. A lunchtime run before an afternoon brainstorming session is a smart strategy.
Toxic cortisol erodes connections between billions of nerve cells, and the hippocampus shrinks under prolonged stress. Exercise unleashes growth factors that physically bolster the brain's infrastructure and make neurons more resilient.
Because you initiate the action, exercise gives you a sense of mastery and self-confidence. You learn to trust that you can handle stress. The mechanisms are more effective than donuts, medicines, or wine — when you feel less stressed after a swim, you are.
The amygdala overwhelms the hippocampus's attempts to put fear in context. Exercise triggers GABA — the brain's major inhibitory neurotransmitter and the primary target of anti-anxiety medication — and physically enlarges the prefrontal cortex that sends cease-and-desist signals.
Running rats grew new neurons, but acrobatic rats on balance beams and rope ladders had a 35% increase in BDNF in the cerebellum. Choose a sport that taxes both systems — tennis, dance, martial arts — or do a 10-minute aerobic warm-up before skill-based training.
Regular moderate exercise most days changes the brain more than occasional intense effort. Thirty minutes of jogging two or three times a week for twelve weeks improved executive function. The more stress you have, the more your body needs to move.
These notes are inspired by direct excerpts and woven together into a readable guide you can follow from start to finish.
By John J. Ratey and Eric Hagerman
The real reason you feel so good when you get your blood pumping is that exercise makes the brain function at its best. That benefit is far more important—and fascinating—than what physical activity does for the body alone. Exercise is crucial to the way we think and feel: it cues the building blocks of learning in the brain, affects mood, anxiety, and attention, guards against stress, reverses some of the effects of aging, and in women can help stave off the sometimes tumultuous effects of hormonal changes.
Most people don’t know that toxic levels of stress erode the connections between the billions of nerve cells in the brain, or that chronic depression shrinks certain areas of it. Conversely, exercise unleashes a cascade of neurochemicals and growth factors that can reverse this process, physically bolstering the brain’s infrastructure.
If exercise came in pill form, it would be plastered across the front page, hailed as the blockbuster drug of the century. In October 2000, researchers from Duke University showed that exercise is better than sertraline (Zoloft) at treating depression—but the story was buried on page fourteen of the Health and Fitness section.
Your brain is running the show. Right now the front of your brain is firing signals about what you’re reading, and how much you absorb depends on whether there is a proper balance of neurochemicals and growth factors to bind neurons together. If you had half an hour of exercise this morning, you’re in the right frame of mind to sit still and focus, and your brain is far more equipped to remember what you read. To cope with anxiousness, for instance, you need to let certain well-worn neural paths grow over while you blaze alternate trails.
Exercise has a profound impact on cognitive abilities and mental health. It is simply one of the best treatments available for most psychiatric problems. The hope is that if you understand how physical activity improves brain function, you’ll be motivated to include it in your life in a positive way, rather than viewing it as something you merely should do.
A pioneering school program called Zero Hour PE demonstrated the exercise–learning connection in action. Students who exercised before class showed a 17 percent improvement in reading and comprehension, compared to 10.7 percent among students who took standard PE later in the day. When the program expanded into the regular curriculum as a first-period class called Learning Readiness PE, literacy students were split between a second-period class—when they were still feeling the effects of exercise—and an eighth-period class. As expected, the second-period group performed best.
“It’s not my job as a PE teacher to make kids fit. My job is to make them know all of the things they need to know to keep themselves fit. Exercise in itself is not fun. It’s work. So if you can make them understand it, show them the benefits—that’s a radical transformation.”
A key lesson from the program is the importance of helping every student find an activity that lets them feel comfortable excelling. When exercise is framed around understanding and personal success rather than competition alone, the transformation is both physical and academic.
In addition to priming your state of mind, exercise influences learning directly at the cellular level, improving the brain’s potential to log in and process new information. When you learn something—a French word or a salsa step—cells morph to encode that information, and the memory physically becomes part of the brain. The brain is flexible, or plastic in the parlance of neuroscientists—more Play-Doh than porcelain. Your thoughts, behavior, and environment reflect back on your neurons, influencing the pattern of connections. Far from being hardwired, the brain is constantly being rewired.
Synaptic signaling: An electrical signal shoots down the axon (outgoing branch) until it reaches the synapse, where a neurotransmitter carries the message across the gap in chemical form. On the receiving side, the neurotransmitter plugs into a receptor—like a key into a lock—turning the signal back into electricity. About 80% of brain signaling is carried out by two neurotransmitters that balance each other: glutamate stirs up activity, and GABA (gamma-aminobutyric acid) clamps it down. When glutamate delivers a signal between two neurons, repeated activation strengthens the attraction—neurons that fire together wire together—making glutamate a crucial ingredient in learning.
Going for a run is like taking a little bit of Prozac and a little bit of Ritalin, because exercise elevates the same neurotransmitters those drugs target. But the deeper explanation is that exercise balances neurotransmitters—along with the rest of the neurochemicals in the brain.
Beyond neurotransmitters, there is another class of master molecules that has dramatically changed our understanding of how connections develop and grow: a family of proteins loosely termed factors, the most prominent being brain-derived neurotrophic factor (BDNF). Whereas neurotransmitters carry out signaling, neurotrophins such as BDNF build and maintain the cell circuitry—the infrastructure itself. When researchers sprinkled BDNF onto neurons in a petri dish, the cells automatically sprouted new branches, producing the same structural growth required for learning. BDNF is a crucial biological link between thought, emotions, and movement—Miracle-Gro for the brain.
Say you’re learning a French word. The first time you hear it, nerve cells recruited for the new circuit fire a glutamate signal between each other. If you never practice again, the attraction between those synapses naturally weakens and you forget. But repeated activation causes the synapses to swell and make stronger connections—a form of cellular adaptation called synaptic plasticity, where BDNF takes center stage. Eventually new dendritic branches sprout, providing more synapses to further solidify the connections. This discovery earned Columbia University neuroscientist Eric Kandel a share of the 2000 Nobel Prize.
Brain scans show that when you learn a new word, the prefrontal cortex lights up with activity. Once the circuit is established and the word is learned, the prefrontal cortex goes dark—it has overseen the initial stages and can leave the responsibility to capable employees while moving on to new challenges. This is how activities like riding a bike become second nature.
In a 2007 study, German researchers found that people learn vocabulary words 20% faster following exercise, and the rate of learning correlated directly with levels of BDNF. People with a gene variation that robs them of BDNF are more likely to have learning deficiencies. BDNF gives the synapses the tools to take in information, process it, associate it, remember it, and put it in context.
However, you can’t just inject BDNF and become smarter. With learning, you have to respond to something in a different way—but the something has to be there. Exercise sparks the master molecule of the learning process, nailing down a direct biological connection between movement and cognitive function. Among people whose minds hold up best over time, three factors turn up consistently: education, self-efficacy, and exercise.
Environmental stimulation of learning, exercise, and social contact causes synapses to form more connections with thicker myelin sheaths, allowing them to fire signals more efficiently. In rodent studies, simply putting a running wheel in a cage had a profound effect on the number of new cells born in the brain. But in order for a new cell to survive and integrate, it has to fire its axon—exercise spawns neurons, and the stimulation of environmental enrichment helps those cells survive.
The body was designed to be pushed, and in pushing our bodies we push our brains too. Learning and memory evolved in concert with the motor functions that allowed our ancestors to track down food.
Exercise improves learning on three levels: (1) it optimizes your mind-set, improving alertness, attention, and motivation; (2) it prepares and encourages nerve cells to bind to one another, the cellular basis for logging in new information; and (3) it spurs the development of new nerve cells from stem cells in the hippocampus.
One thing scientists know for sure: you can’t learn difficult material while exercising at high intensity, because blood is shunted away from the prefrontal cortex, hampering executive function. College students perform poorly on tests of complex learning while working out at 70–80% of their maximum heart rate. But blood flow shifts back almost immediately after you finish, making the post-exercise window the perfect time to focus on a project that demands sharp thinking and complex analysis. If you have an important afternoon brainstorming session, going for a short, intense run during lunchtime is a smart idea.
As for how much aerobic exercise you need, one scientifically sound study from Japan found that jogging thirty minutes just two or three times a week for twelve weeks improved executive function. But it’s important to mix in activity that demands coordination beyond putting one foot in front of the other. In a comparison study, rats trained on complex motor skills—walking across balance beams, unstable objects, and elastic rope ladders—showed a 35% increase of BDNF in the cerebellum, whereas running rats had none in that area. Aerobic exercise and complex activity have different beneficial effects on the brain.
Choose a sport that simultaneously taxes the cardiovascular system and the brain—tennis is a good example—or do a ten-minute aerobic warm-up before something nonaerobic and skill-based, such as rock climbing or balance drills. Learning tango, for instance, demands reacting to another person, which puts further demands on attention, judgment, and precision of movement, exponentially increasing complexity. Add in the fun and social aspect, and you’re activating the brain and muscles all the way down through the system.
Neurons get broken down and built up just like muscles—stressing them makes them more resilient. This is how exercise forces the body and mind to adapt. If we strip away everything else, our ingrained reaction to stress is about focusing on the danger, fueling the reaction, and logging in the experience for future reference—which can be thought of as wisdom.
The fight-or-flight response calls into action several of the body’s most powerful hormones and scores of neurochemicals in the brain. The amygdala, the brain’s panic button, sets off the chain reaction on receiving sensory input about a possible threat to the body’s equilibrium. Its job is to assign intensity to incoming information, which may or may not be obviously survival-related. It’s not just about fear but any intense emotional state, including euphoria or sexual arousal—winning the lottery or dining with a supermodel can trigger it. Our brains don’t distinguish between “good” and “bad” demands on the system; in evolutionary terms, good fortune and a good date are related to survival—prospering and procreating.
Norepinephrine arouses attention; dopamine sharpens and focuses it. An imbalance of these neurotransmitters is one reason some people with ADHD come across as stress junkies—they have to get stressed to focus. This is a primary factor in procrastination: people learn to wait until the deadline looms and stress unleashes the neurochemicals they need to sit down and do the work.
Cortisol takes over for epinephrine and signals the liver to make more glucose available while blocking insulin receptors at nonessential tissues, shuttling fuel only to areas important for fight-or-flight. The strategy is to make the body insulin-resistant so the brain has enough glucose. Cortisol also restocks energy stores by converting protein into glycogen and storing fat. If this continues unabated, as in chronic stress, the process amasses surplus fuel around the abdomen as belly fat. (Unrelenting cortisol also explains why some marathon runners carry a slight paunch despite all their training—their bodies never get a chance to adequately recover.)
Operating on a fixed budget of fuel, the brain has evolved to shift energy resources as necessary, meaning that mental processing is competitive. If one structure is active, it must come at the expense of another. One problem with chronic stress is that if the HPA axis is guzzling all the fuel to keep the system on alert, the thinking parts of the brain are being robbed of energy.
During stress, beefed-up cells cement survival memories and shield those neurons from other demands. A neuron might be part of any number of memories, but if a potential memory comes along during stress, it has a more difficult time recruiting neurons for its new circuit. This likely explains why memories unrelated to the stressor are blocked during the stress response. Constantly high levels of cortisol—from chronic stress—make it hard to learn new material and explain why depressed people have trouble learning. It’s not just lack of motivation; the hippocampal neurons have bolstered their glutamate machinery and shut out less important stimuli—they’re obsessed with the stress. Excess cortisol can also block access to existing memories, explaining how people can forget where the fire exit is during an actual fire. The neurological point of fire drills is to make those circuits stronger and burn in the memory.
The great paradox of the modern age may be that there is not more hardship, just more news—and too much of it. The 24/7 streaming torrent of tragedy and demands keeps the amygdala flying. It’s no wonder that obesity has doubled in the past twenty years—our lifestyle today is both more stressful and more sedentary.
The stress response is elegantly adaptive behavior, but because it doesn’t get you very far in today’s world, there’s no outlet for all that energy buildup. You have to make a conscious effort to initiate the physical component of fight or flight.
Cellular stress takes two forms. Metabolic stress happens when cells can’t produce adequate ATP because glucose can’t get into the cell or there isn’t enough of it. Excitotoxic stress occurs when there is so much glutamate activity that there isn’t enough ATP to keep up with the energy demand. If this continues without recovery, dendrites shrink back and eventually cause cell death—neurodegeneration, the mechanism underlying diseases such as Alzheimer’s, Parkinson’s, and aging itself. Research into these diseases has revealed the body’s natural countermeasures: mice and rats given a third of their normal calories live up to 40% longer than average, because mild cellular stress unleashes protective molecules—the same ones triggered by aerobic exercise.
The best way to build up your brain’s stress defenses is by bringing mild stress on yourself: using the brain to learn, restricting calories, exercising, and eating your vegetables. The advantage of exercise specifically is that it ramps up growth factors more than other stimuli do.
Sometimes the fight-or-flight switch gets stuck in the on position. It can be genetic: those whose parents suffered from hypertension show elevated cortisol levels twenty-four hours after a stressful event. Or it can be environmental: prenatal rats whose mothers are subjected to repeated stress grow up with a lower stress threshold—they get stressed more easily, both physically and psychologically.
It’s what happens after exercise that optimizes the brain. Exercise increases the efficiency of intercellular energy production, allowing neurons to meet fuel demands without increasing toxic oxidative stress. You get waste buildup, but you also get the enzymes that chew it up, plus a janitorial service that disposes of broken DNA and other by-products of normal cellular use and aging—both of which help prevent cancer and neurodegeneration. While exercise induces the stress response, if the activity level isn’t extreme, it shouldn’t flood the system with cortisol.
The stress of exercise is predictable and controllable because you’re initiating the action—and these two variables are key to psychology. With exercise, you gain a sense of mastery and self-confidence. As you develop awareness of your own ability to manage stress without relying on negative coping mechanisms, you increase your ability to snap out of it. The mechanisms by which exercise changes how you think and feel are far more effective than donuts, medicines, and wine. When you say you feel less stressed after a swim or even a fast walk, you are.
Chronic stress is linked to some of our most deadly diseases. Repeated spikes in blood pressure can damage vessels, leading to plaque buildup and atherosclerosis. An unchecked stress response stockpiles dangerous abdominal fat.
A 2004 study at Leeds Metropolitan University found that workers who used their company’s gym were more productive and felt better able to handle their workloads. Among 210 participants—mostly taking aerobics classes, though some lifted weights or practiced yoga—65% fared better in interacting with colleagues, managing time, and meeting deadlines on days they exercised. They also felt less fatigued in the afternoon, despite expending energy at lunchtime.
In recent years, doctors have started recommending exercise for cancer patients, both to boost the immune response and to fend off stress and depression. Activity is clearly a factor: twenty-three of thirty-five studies show an increased risk of breast cancer for inactive women; physically active people have 50% less chance of developing colon cancer; and active men over sixty-five have a 70% lower chance of developing advanced, typically fatal prostate cancer. Just keep in mind that the more stress you have, the more your body needs to move to keep your brain running smoothly.
When you’re facing an upcoming speech or a confrontation with your boss, anxiety sharpens your attention so you can meet the challenge. Physical symptoms range from feeling tense, jittery, and short of breath to a racing heart, sweating, and—in full-blown panic attacks—severe chest pains. Emotionally, what you feel is fear. In neurological terms, fear is the memory of danger. If you suffer from an anxiety disorder, the brain constantly replays that memory, forcing you to live in that fear.
It all starts when the amygdala sounds the survival call, but unlike the normal stress response, in anxiety the all-clear signal isn’t working properly. Your cognitive processors fail to tell you the problem has passed and you can relax. One correlation scientists have found among people with generalized anxiety disorder is brain scans showing the area of the prefrontal cortex responsible for sending cease-and-desist signals to the amygdala as being smaller than it should be. Left unchecked, the overexcited amygdala tags too many situations as survival challenges and burns them into memory. The fear memories form connections with each other and the anxiety snowballs. Eventually, the amygdala overwhelms the hippocampus’s attempts to put the fear in context. As the snowball grows and more memories become associated with fear, your world shrinks.
A huge part of the problem with social anxiety is that the more you withdraw, the less practice you get interacting, and the scarier the prospect becomes. Just as anxiety can feed on itself, so can courage.
The majority of studies show that aerobic exercise significantly alleviates symptoms of any anxiety disorder, and it also helps reduce normal feelings of anxiousness. Over time, you teach the brain that the symptoms don’t always spell doom and that you can survive—you’re reprogramming the cognitive misinterpretation. Moving the body also triggers the release of GABA, the brain’s major inhibitory neurotransmitter and the primary target for most antianxiety medicines.
While you can’t erase the original fear memory, you can essentially drown it out by creating a new memory and reinforcing it. By building up parallel circuitry, the brain creates a neutral alternative to the expected anxiety, learning that everything is OK. By wiring in the correct interpretation, the trigger is disconnected from the typical response. Scientists call it reattribution. You can force the brain to trade fear memories for neutral or positive ones through cognitive behavioral therapy (CBT). Everyone’s initial instinct in the face of anxiety is to avoid the situation, but doing just the opposite—engaging in cognitive restructuring—uses the body to cure the brain.
Because anxiety brings the sympathetic nervous system into play, rapid, shallow breathing expels too much carbon dioxide, dropping the blood’s pH level and triggering an alarm from the brain stem that makes muscles constrict even more. This is why breathing into a paper bag stops hyperventilation: it forces you to rebreathe the carbon dioxide.
There’s nothing wrong with taking medicine, but if you can achieve the same results through exercise, you build confidence in your own ability to cope—a significant advantage for anyone, not just patients with full-blown anxiety disorders.
For panic disorder, combining medicine with exercise can be a powerful approach. Medicine provides immediate safety, and exercise gets at the fundamentals of anxiety. Because panic disorder is so frightening, starting with medicine helps diffuse the trigger, but it doesn’t necessarily lead to permanent change—the relearning process is needed for long-term relief.
One long-term study followed seven hundred children into adulthood. Of those who suffered from anxiety as children, most grew out of it. But of those who developed a mood disorder, two-thirds of the time the problem started as preadolescent anxiety. What’s tragic is that anxiety is relatively easy to treat but often goes undiagnosed in children—the anxious kids sit quietly at the back of the class, terrified, and nobody notices because they’re well behaved. Meanwhile, negative patterns are wearing into their brains. For anyone who is panicky, exercising with somebody is the number-one thing to do: it offers a sense of safety and increases serotonin immediately just from being around another person.
The farther you get from your last panic episode, the less likely you are to have another one. The same holds for any brand and any degree of anxiety. The more your life changes, the more you engage with the world, the more likely you are to put the anxiety behind you for good.
Depression can be thought of as an erosion of connections—in your life as well as between your brain cells. Endorphins, the body’s morphine-like substances, gave us the expression “runner’s high” when elevated levels were detected in the blood of runners. But the story goes much deeper than endorphins.
Nobody had done a scientifically sound head-to-head comparison of exercise and antidepressants until the landmark SMILE study (Standard Medical Intervention and Long-term Exercise) at Duke University in 1999. Researchers randomly divided 156 patients into three groups: Zoloft, exercise, or a combination of the two. The exercise group was assigned supervised walking or jogging at 70–85% of aerobic capacity for thirty minutes, three times a week. The results: all three groups showed a significant drop in depression, and about half of each group was completely in remission. Another 13% experienced fewer symptoms but didn’t fully recover. Exercise was as effective as medication.
If everyone knew that exercise worked as well as Zoloft, it could put a real dent in the disease. Subsequent research showed that patients who weren’t responding to antidepressants lowered their depression scores by 10.4 points on a 17-point scale—a huge drop—after twelve weeks of exercise.
In 1996, research showed that the hippocampus of depressed patients was up to 15% smaller compared to healthy controls, and the degree of shrinkage was directly related to the length of depression. High levels of cortisol kill neurons in the hippocampus. If you flood a neuron with cortisol, its connections retract, fewer synapses develop, and dendrites wither. This communication breakdown could partly explain why a depressed brain gets locked into negative thoughts—it’s recycling a negative memory because it can’t branch out to form alternative connections.
Depression as a survival instinct: Psychiatrist Alexander Niculescu sees depression as a mechanism to conserve resources in an environment void of hope—“to keep still and stay out of harm’s way.” It’s a form of hibernation: when the emotional landscape turns wintry, our neurobiology tells us to stay inside—except it can last much longer than a season.
Redefining depression as a connectivity issue helps explain the wide range of symptoms. It’s not just feeling empty, helpless, and hopeless—it affects learning, attention, energy, and motivation, involving different parts of the thinking brain. Depression also shuts down the drive to sleep, eat, have sex, and generally look after ourselves on a primitive level.
Exercise boosts BDNF at least as much as antidepressants, and sometimes more, in the hippocampus. One study showed combining exercise with antidepressants spiked BDNF by 250%. Conversely, mice bred to produce 50% less BDNF don’t respond well to antidepressants and are significantly slower to try to escape stress, suggesting BDNF is a necessary ingredient for the drugs to work.
What makes aerobic exercise so powerful is that it’s our evolutionary method of generating the spark. It lights a fire on every level of the brain, from stoking the neurons’ metabolic furnaces to forging the structures that transmit information from synapse to synapse. Part of initial recovery from depression is simply getting moving. Going outside for a walk is the best kind of behavioral therapy—it doesn’t require elaborate planning and doesn’t put you into a negative spin. The physical activity is quickly reinforcing because it proves you can initiate something. If your prefrontal cortex has been offline for a while, exercise reprograms it. You begin to see trees instead of a barren wasteland. When you see yourself moving, that alone is an achievement—proof that you can help yourself.
Because humans are social animals, the ideal is to choose a form of exercise that encourages making connections and takes place outside or in an environment that stimulates the senses. Asking someone to join you and putting yourself in a new setting give newly hatched neurons a powerful reason for being: new connections need to form to represent the sensory stimulation.
In a study dividing eighty depressed patients into groups of varying intensity, the high-intensity groups—burning an average of 1,400 calories (eight calories per pound) over three or five sessions per week—cut their depression scores in half, regardless of frequency. The low-intensity groups (560 calories, three calories per pound) lowered scores by only a third, about the same as the stretching control. Practically, this means: some exercise is good, more is better. The high dose is based on public health recommendations of about thirty minutes of moderate aerobic activity on most days—roughly three hours per week for a 150-pound person.
Giving bipolar patients a stable social routine has been shown to improve long-term outcomes, and exercise is only recently making its way into treatment protocols for bipolar disorder.
In some ways, exercise is even more important for prevention than treatment. One of the first symptoms of depression, even before your mood drops, is sleep disturbance—you can’t get up, can’t get to sleep, or both. Then you lose your energy, then your interest. The key is to get moving immediately and not stop. Set up a schedule for a daily walk, run, jog, bike ride, or dance class. If you can’t sleep, go for a walk in the dawn light and do it every day. Burn those 1,400 calories as if your life depended on it and nip it in the bud.
While it’s true that people with ADHD “just need to get motivated,” motivation is biological. A child who can’t pay attention in class but sits perfectly still for hours playing a video game isn’t simply choosing when to focus. Functional MRI scans reveal distinct differences in activity at the reward center—a cluster of dopamine neurons called the nucleus accumbens—which is responsible for doling out pleasure or satisfaction signals to the prefrontal cortex, providing the drive to focus. The sort of stimulation that activates the reward center enough to capture the brain’s attention varies from person to person.
Attention variability disorder: The ability to hyperfocus is paradoxically a common trait of ADHD, leading many people to miss the diagnosis. The glitch in the attention system isn’t strictly a deficit—it’s an inability to direct attention or to focus on command. The deficit is one of consistency.
It’s easy to get distracted in today’s world. The amount of data is doubling every few years, but our attention system was built to make sense of the environment as it existed ten thousand years ago. Experts estimate that just over 4% of American adults—thirteen million people—have ADHD, but the remaining 96% aren’t completely free of attention problems either. Everyone suffers from fleeting attention to some degree, and there are varying degrees of severity—shadow syndromes that don’t necessarily meet the full diagnostic checklist.
Countless parents observe the same thing about their ADHD children: the child is so much better when doing martial arts, ballet, figure skating, gymnastics, or less traditional sports like rock climbing, mountain biking, whitewater paddling, or skateboarding. These activities require complex movements in the midst of heavy exertion. The combination of challenging the brain and the body has a greater positive impact than aerobic exercise alone. One study found that ADHD boys ages eight to eleven participating in martial arts twice a week improved their behavior and performance on multiple measures compared to those on a typical aerobic exercise program—though both kinds of exercise led to dramatic improvement over nonactive controls.
There is a lot of overlap between attention, consciousness, and movement. The attention circuits are jointly regulated by norepinephrine and dopamine, which are so similar on a molecular level that they can plug into each other’s receptors. These are the chemicals targeted by ADHD medications. The reward center needs to be sufficiently activated before it tells the prefrontal cortex that something is worth paying attention to—this engages the prioritizing aspect of executive function, a central component of motivation. Essentially, the brain won’t do much unless the reward center is responsive. People with ADHD favor immediate gratification over mundane tasks that help them down the road—they are prisoners of the present. A failure of working memory is also why they are terrible at keeping track of time and prone to procrastination; they literally forget to worry about the passing time.
The cerebellum takes up just 10% of the brain’s volume but contains half of our neurons. For decades it was assumed to govern only movement, but it also regulates certain brain systems, updating and managing the flow of information to keep it moving seamlessly. The areas of the brain that control physical movement also coordinate the flow of information—this is where the attention system ties in with exercise.
Dopamine works like transmission fluid: if there’s not enough, as in ADHD, attention can’t easily be shifted or can only be shifted all the way into high gear. This parallel matters for Parkinson’s disease as well—neurologists now recommend daily exercise in the early stages to stave off symptoms. In rat studies, animals forced to run on a treadmill twice daily in the ten days after induced Parkinson’s maintained normal dopamine levels and their motor skills didn’t deteriorate. In one human study, intensive activity improved motor ability and mood, with positive effects lasting at least six weeks after the exercise stopped.
A controversial treatment for dyslexia—which occurs in about 30% of ADHD patients—relies entirely on physical movements to train the cerebellum. DDAT (dyslexia, dyspraxia, and attention treatment) is based on the theory that a disruption in the brain’s ability to coordinate movement might be responsible for eye-tracking problems and thus difficulties in reading and writing. Most children with dyslexia perform worse than average on tests of cerebellar function. DDAT involves practicing simple motor-skills drills twice a day for ten minutes. In 2003, British researchers tested it on thirty-five children with dyslexia and declared the results “astounding”—after six months, students showed significant improvement in reading and writing fluency, eye movement, cognitive skills, dexterity, and balance. Notably, within a large population of prisoners, more than 80% had had serious learning problems as children.
With regular exercise, you can raise the baseline levels of dopamine and norepinephrine by spurring the growth of new receptors in certain brain areas. Exercise also increases norepinephrine, and the more complex the exercise, the better: rats practicing complex motor skills improved BDNF levels more dramatically than those running on a treadmill, suggesting growth is happening in the cerebellum.
Scientists are now characterizing behaviors such as gambling, compulsive shopping, and overeating in the same biological terms used for substance abuse. The common denominator is an out-of-control reward system, which some people are born with and some develop. By studying how dopamine works as the key messenger in the reward system, scientists have drawn a distinction between liking something—the actual experience of pleasure—and wanting it—the motivational state, the willingness to work for rewards. Dopamine is involved in wanting but not in liking.
Typically, when you learn something, the connections stabilize and dopamine levels tail off over time. With addiction, especially drug addiction, dopamine floods the system with each use, reinforcing the memory and pushing other stimuli into the background. Drugs such as cocaine and amphetamine make dendrites in the nucleus accumbens bloom, increasing synaptic connections. These changes can remain months or even years after the drugs are stopped, which is why relapse is so easy. If you continually subject your brain to a dopamine overload, the number of receptors dwindles—so the more drugs you take, the more you need to feel the same rush. The same is true of overeating.
The prefrontal cortex doesn’t fully develop until well into our twenties, which could explain why most people who experiment with drugs and get hooked do so as teenagers or during early adulthood, when their inhibition hasn’t fully developed. They end up with a hypersensitive system that wants drugs, and they make very bad decisions.
Exercise serves as a conduit for shifting focus to a more productive life. It offsets the feelings of hopelessness and uselessness that many drug users experience. The routine and physical activity get the brain engaged and the mind moving in a direction other than toward the drug, reprogramming the basal ganglia to wire in an alternative reflexive behavior. Exercise presents the addict with a compelling alternative: the goals, feeling, challenge, pleasure and pain, accomplishment, physical well-being, and self-esteem that come with it.
Exercise fights the urge to smoke because in addition to smoothly increasing dopamine, it also lowers anxiety, tension, and stress levels—the physical irritability that makes quitting so difficult. Exercise can fend off cravings for fifty minutes and double or triple the interval to the next cigarette. Since one of the withdrawal symptoms of nicotine is impaired focus, the fact that exercise sharpens thinking comes into play as well. People are more impulsive when they feel lousy, and both strength training and aerobic exercise decrease symptoms of depression in recovering alcoholics and smokers who have quit.
Self-regulation is a resource that can be depleted but also recharged like a muscle. The more you use this faculty, the stronger it gets. Exercise is by far the best form of self-regulation we have.
As one woman put it: “The week before my period I have to do an hour of cardio four days a week or I can’t stand myself.” Exercise plays a critical role at every stage of a woman’s hormonal life—from menstrual cycles through pregnancy, postpartum, and menopause.
German researchers tested whether exercise would have any impact on labor pain by bringing a stationary bicycle into the labor suite. Among fifty women who pedaled for periods of twenty minutes and rated their pain levels, 84% said contractions were less painful during exercise than at rest, and their ratings were inversely proportional to endorphin levels. The researchers concluded that exercising during labor is safe for the fetus, a stimulus to uterine contractions, and a source of pain relief.
For 10–15% of new mothers, postpartum depression strikes after everything initially seems fine, and it can stick around for a year or more. Exercise may be even more effective for new moms experiencing depression than for the general population because it normalizes neurotransmitter levels.
Women over sixty-five who reported higher levels of physical activity were 50% less likely than their inactive peers—women and men alike—to develop any form of dementia. The best type of aerobic activity is whatever allows you to build it into your lifestyle.
The advice that surprises people most is that it’s important to keep up exercise during pregnancy—a recommendation now endorsed by the American College of Obstetricians and Gynecologists, which specifies thirty minutes of moderate-intensity aerobic activity every day for healthy pregnant women. It’s important to get clearance from your obstetrician, but it’s safe for most women. Equally important is picking up your routine as soon as possible after the baby is born, ideally within a few weeks. Although it seems contradictory, moving will actually reduce fatigue, and it melts away anxiety and depression.
When women are younger, one of the big motivations to exercise is to stay trim, and that’s fine—use whatever gets you going. But even as your body changes, exercise will keep your mind firm and taut. In this state of mental fitness, you’ll be well equipped to handle the hormonal fluctuations that every woman experiences throughout her life.
The average seventy-five-year-old suffers from three chronic medical conditions and takes five prescription medicines. Among those over sixty-five, most suffer from hypertension, more than two-thirds are overweight, and nearly 20% have diabetes (which triples the chance of heart disease). The leading killers—heart disease, cancer, and stroke—together account for 61% of all deaths in this age group. The same things that kill the body kill the brain, and the latest research confirms how lifestyle influences the mental hazards of aging. The measures you’d take to guard against diabetes also balance insulin levels in the brain and shore up neurons against metabolic stress. Running to lower blood pressure also keeps brain capillaries from collapsing or corroding. Lifting weights releases growth factors that make dendrites bloom. Taking omega-3 fatty acids for mental acuity also strengthens bones. The mental and physical diseases of old age are tied together through the cardiovascular and metabolic systems—which explains why obese people are twice as likely to suffer from dementia and why heart disease puts you at far greater risk of Alzheimer’s.
It’s good that cells be periodically subjected to mild stress because it improves their ability to cope with more severe stress. Exercise is preventive medicine as well as an antidote. Age happens—there’s nothing you can do about the why, but you can do something about the how and the when.
Estrogen in women and testosterone in men decrease with age, leading to shifts in mood or a loss of vigor and interest. Depression is a risk factor for dementia because of its corrosive effects on the hippocampus: if cortisol stays elevated, it eats away at synapses. People who feel lonely are twice as likely to develop Alzheimer’s, and exercise reduces depression—it’s even better than Zoloft at keeping people from relapsing.
The one proven way to live longer (in lab rats at least) is to consume fewer calories: rodents eating 30% fewer calories live up to 40% longer than those eating freely.
The core argument of this book—that exercise is the single most powerful tool you have to optimize your brain function—is based on evidence from hundreds of research papers, most published only within the past decade. Body and brain are connected. Why not take care of both?
The most important thing is to do something, and to start. For the sedentary—especially if inactivity is due to depression—taking that first step may seem impossible. Some people face a catch-22: they can’t start because they don’t have the energy, and they don’t have the energy because they’re not exercising. This is a very real problem, not simply an issue of willpower. The key is to attack the business of starting as a challenge in itself. It’s also crucial to build in recovery time so your body and brain have the opportunity to bounce back.
Human Growth Hormone (HGH): One of the key differences between moderate and high-intensity exercise is that once you get into the anaerobic range, the pituitary gland unleashes HGH—what life-extension groups call the fountain of youth. HGH levels naturally decrease over your life span, dwindling to a tenth of childhood levels by middle age. A sedentary lifestyle—with high cortisol, insulin resistance, and excess fatty acids—exacerbates this decline. HGH is the body’s master craftsman: it burns belly fat, layers on muscle fiber, and pumps up brain volume. Researchers believe it can reverse the brain volume loss that occurs with aging.
High-intensity exercise toughens you up both physiologically and psychologically. Yet you don’t need to go to extremes. A single thirty-second sprint on a stationary bike generated a sixfold increase in HGH, peaking two hours after the sprint. In another study, volunteers who did two three-minute sprints during a forty-minute treadmill run showed significantly higher increases in BDNF and norepinephrine compared to subjects who stayed at low intensity. Doing squats doubled HGH levels compared with running at high intensity for thirty minutes.
Every day is best, but even intermittent exercise works wonders. The upper end of high-intensity exercise is sometimes painful but always powerful territory.
Finding the right social context can be the key to sticking with exercise. For some adults, being part of a team gets them hooked—whether it’s a city basketball program, an adult soccer league, or Masters swimming. Maybe walking with the one you love is the answer, or maybe learning tae kwon do, or discovering a passion for rock climbing. The point is cooperation over competition, and finding the activity that makes you want to come back.