PDF Summary:Spark, by John Ratey

Do you exercise enough? You know it’s good for your overall health—but do you know it’s also vital for your brain? John Ratey is an associate clinical professor of psychiatry at Harvard, and he’s been convinced by the scientific and clinical evidence—our brains are built to move. He’s seen firsthand how patients struggling with addiction, anxiety, and depression are transformed by exercise.

In Spark, he discusses the evolutionary origins of the mind-body connection and how exercise optimizes brain function and supports mental health. In this guide, we’ll examine these theories as well as Ratey’s recommendations for how to incorporate exercise into your life, exploring which exercise is most beneficial and how you can stick to a routine.

Along the way, we’ll discuss how the theories of other experts align with or differ from Ratey’s ideas, and we’ll update the science where new insights have emerged in the years since the book’s release.

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This is part of the reason soldiers prepare for real battle by being exposed to physically demanding and threatening training regimens. If your neural network is more connected, and you are less apt to feel afraid, your brain’s executive functions will continue to work in the face of potentially fearful situations. This will keep you from entering into a less-controlled reflexive response governed by the amygdala.

Exercise Is a Mild Stress

Ratey contends that exercise, as a form of mild acute stress, is like an inoculant that builds resilience, toning all the machinery of the brain and body and tamping down our trigger-happy stress response system. He points out that this effect is largely a consequence of the way our cells recover after exercise-induced stress—this is part of the activity and recovery process of the body’s stress response. In addition to this recovery mechanism, the broader effects of exercise on the brain condition us to handle stress better.

New Insights Into How Exercise Acts Like an Inoculant

A recent study has added to our understanding of how exercise acts like an inoculant: Exercise increases the amount of galanin in the brain. Galanin is a neuropeptide that exists in animals of all kinds, and not having enough of it has been linked to heightened stress sensitivity and stress-related disorders, such as anxiety and depression. Knowing this, clinicians have tried to raise galanin levels in patients by using medications, but this doesn’t work in many cases.

The new study found that mice made to exercise had more galanin in their brains than those that didn’t exercise—and that those higher galanin levels made them more resistant to stressors they were later exposed to. This finding supports the use of exercise as a treatment for raising galanin levels and increasing stress resilience.

Exercise Improves Our Mental Health

In this section, we’ll explore Ratey’s theories on how and why exercise benefits our mental health. We’ll first discuss neurotransmitters, which are largely responsible for psychiatric well-being, and then we’ll briefly touch on the various mental health conditions Ratey addresses, summarizing the main ways exercise helps. In each case, Ratey refers to the science and to stories from his clinical practice to make his point.

(Shortform note: Defining stress narrowly, in terms of cell biology, positions stress as a through-line in all the mental health concerns Ratey goes on to discuss. He isn’t as explicit about this as he could be, but bear in mind that each condition has some form of stress as a component—whether it’s a cause, a symptom, or some combination of the two. Accordingly, the way exercise combats the negative effects of stress generally applies to the other concerns he explores, such as anxiety, depression, and so on.)

Exercise Balances Neurotransmitters in the Brain

Neurotransmitters are chemicals that regulate the signals passing along the brain’s neural network. When there's an imbalance of neurotransmitters we can experience difficulties such as anxiety, depression, scattered focus, memory loss, and more. Too much glutamate, for instance, leads to a signal overload that can cause excitotoxic stress. Too little gamma-aminobutyric acid (GABA) undercuts your brain’s ability to stop the signals.

The functioning of these two neurotransmitters is further regulated by three other neurotransmitters you may have heard of: serotonin, norepinephrine, and dopamine. The messages that end up getting transmitted throughout the brain are largely regulated by these three chemicals. There’s overlap between their functions, but:

• Serotonin is largely responsible for signals having to do with mood.
• Norepinephrine influences attention and arousal.
• Dopamine works in the realm of motivation.

These are the three chemicals targeted by most psychiatric medications. Selective serotonin reuptake inhibitors (SSRIs) such as Lexapro, for example, are used to regulate the disruptive mood states associated with depression by increasing serotonin levels in the brain.

Ratey supports the use of such medications and is careful not to suggest that exercise should be relied on to the exclusion of drugs in particular cases. Such decisions are best made under the guidance of physicians familiar with the case. Nevertheless, Ratey argues that exercise helps to bring all these chemicals into balance by stimulating the release of each of these neurotransmitters in optimal amounts for mental health.

Exercise as Treatment

A theme of Ratey’s approach to mental illness is that you can influence your mind by using your body—exercise, in this light, is a form of treatment. This diverges with another approach that has been dominant in the field since the 1980s—prescribing medications.

This practice emerged with the idea that common mental disorders were due to chemical imbalances in the brain. It was merely the latest in a series of ideas that prompted treatment strategies: In the era of eugenics (the belief that humans could be improved by selective breeding) poor mental health was seen as a product of genetically inferior brain anatomy—lobotomies (removing parts of the brain) and forced sterilization (to weed out “bad genes” from the human gene pool) were preferred treatments.

Later, in the Freudian era, psychologists believed that thoughts and behaviors came from the subconscious mind, and psychoanalysis became the preferred treatment

The more recent pharmaceutical approach to treatment seeks to restore chemical balance in the brain, but even that approach has proven to be an incomplete treatment for most mental health issues. Some experts are even convinced that the rise of psychiatric medications has contributed to the prevalence of mental health illness today. They cite evidence indicating that the use of psychiatric drugs leads to chronic psychiatric disorders with more severe symptoms for many patients.

Using exercise as a treatment in the way Ratey describes seems to have none of these adverse effects, and, increasingly other clinicians also advocate using it this way.

Anxiety

Anxiety is a component of your brain’s stress-response system; it’s a natural response to legitimate threats. When it becomes overly heightened, turning into an undue fear response to misperceived threats, it becomes a disorder. According to Ratey, exercise alleviates both the symptoms and the state of anxiety by calming our bodies, increasing our sense of autonomy, and retraining our brains to better regulate and reduce fear signals.

Exercise Improves Anxiety Complications of Covid-19

Research has shown that the Covid-19 virus causes physiological changes in the brain that induce anxiety. A recent study has found that physical exercise directly counters this anxiety, and in an unexplained way—it replicates some of the mechanisms by which the virus heightens anxiety, but in doing so, it lowers anxiety.

The virus increases anxiety by attaching itself to a particular enzyme, causing that enzyme to be released in greater amounts. This leads to inflammation, the death of neurons, and heightened anxiety signals in the brains of those infected.

Exercise also causes this enzyme to be released, but the result is the opposite of the virus’s—a general improvement in mental health and less anxiety. The exact reason the outcome is so different when exercise increases this enzyme as opposed to when the virus increases it hasn’t been definitively determined. Regardless, it demonstrates another biological link between exercise and the control of anxiety.

Depression

Ratey argues that depression should be thought of as a breakdown in neural communication. In the depressed brain, the neural network breaks down, disconnecting brain regions from one another. This causes critical parts of the brain to atrophy. A lack of neurotransmitters compounds this state leaving the brain unable to kickstart its attention and motivation tools. The effects of exercise can break this vicious circle by rebuilding neural connections, restoring healthy brain chemistry, powering neurogenesis, and nurturing a sense of hope.

The Current View of Depression

Ratey’s view of depression as a breakdown in neural communication fits with the current consensus about the condition. However, psychologists haven’t always seen depression this way.

It was once thought that depression was primarily caused by a lack of neurotransmitters like serotonin and dopamine. This is part of the picture, but the current understanding is broader: It’s now understood that stress hormones degrade the neural network and atrophy the amygdala and prefrontal cortex in the depressed brain. These parts of the brain are responsible for threat detection and cognitive control, respectively. The result is that the depressed brain has a diminished capacity to respond, make choices, and learn, among other things.

Addiction

Addiction co-opts our attention resources by making the brain focus exclusively on the object of addiction. For the drug addict, for instance, an overload of dopamine in the brain—triggered by the drug of choice—tricks the brain into attending only to that trigger as if it’s a matter of life or death. Exercise breaks this fixation by retraining the brain’s motivation system—weaning it off an unnatural dopamine fix in favor of a balance of healthy neurochemicals.

(Shortform note: Substance abuse and addiction are common markers of trauma. Bessel van der Kolk discusses the unique nature of traumatic memories in The Body Keeps the Score. Such memories alter the makeup of the brain itself and often leave the victim feeling fearful and powerless. A key aspect of Ratey’s insights on exercise and addiction is that exercise can give us a sense of accomplishment that helps to overcome this powerless feeling.)

ADHD

Ratey argues that people with ADHD have functional but poorly regulated attention systems in the brain. This is caused by low levels of dopamine and norepinephrine in the ADHD brain, which undermine its ability to prioritize among distractions, sustain motivation, and combat impulses. Exercise causes brain cells to secrete these key neurotransmitters, builds coordination between the brain’s attention resources, and conditions the systems that support continued attention regulation. In particular, exercises requiring some structure, risk, or coordination (for example, martial arts) seem to be especially effective in harnessing the attention resources of the ADHD brain.

Ratey’s View of ADHD

Ratey has done a lot of work in the field of ADHD, and his 1994 book, Driven to Distraction, co-authored with Edward Hallowell, is often touted as a valuable resource for those dealing with ADHD. Their approach sought to overturn misconceptions about the condition, such as the notion that it only occurred in children or that it was a consequence of laziness or too much sugar. Hallowell and Ratey instead saw ADHD in neurological terms and offered insights into how adults and children with ADHD might manage their distractibility and lean into the strengths of their brain function. His advice here on exercise and ADHD is informed by this history.

Two Special Cases: Aging and Women’s Issues

We’ve seen how exercise helps us learn, regulate stress, and maintain mental health. Two significant consequences of this that Ratey discusses are that exercise protects the aging brain and helps regulate the unique hormonal fluctuations women face over the course of their lives.

Getting Old

For all of us, Ratey contends that the toll a lifetime of stress takes on the brain becomes hard to escape. Characteristic features of aging, such as cognitive decline, depression, and dementia, are at least partially caused by the body’s cells being worn down by the stressors of life.

Ratey argues that as your body becomes equipped to handle stress through exercise, it becomes better able to preserve its resources against the negative effects of aging. For example, as neurons wear out in the brain, the neural network thins—exercise counteracts this loss by supporting neuroplasticity and neurogenesis.

(Shortform note: Researchers have recently found that exercise has a neuroprotective role in staving off cell degeneration caused especially by aging, Parkinson’s, and Alzheimer’s. They advise that exercise should be used as an add-on therapy, together with other forms of treatment, to generate the most benefits.)

Women

Women face unique stressors related to menstruation, pregnancy, and menopause. The hormone fluctuations that attend each of these can lead to anxiety, depression, and attention issues, among other things. During pregnancy, maternal stress can have severe impacts on the fetus.

(Shortform note: A recent analysis found a strong correlation between exercise and the reduction of estrogen. High levels of estrogen have been linked to breast cancer. Subjects who exercised—especially at higher intensities—showed a modest reduction in the total levels of one form of estrogen.)

Ratey contends that exercise has a powerfully stabilizing effect in the midst of all the hormonal fluctuations women face in life. Strikingly, he notes that some data suggest it’s even capable of reversing some of the negative effects fetal alcohol syndrome has on the baby.

(Shortform note: Since the publication of Spark, researchers have continued to examine the impact of exercise on children with executive-function disorders, including fetal alcohol syndrome (FASD). The analysis found that children with FASD who exercised showed major gains in the areas of working memory and response inhibition, and they were also significant for attention. Another noteworthy finding of the analysis is that exercise-induced gains were higher for children with FASD and autism-spectrum disorders than they were for children with ADHD.)

Building a Routine and Making It Stick

We’ve seen numerous ways exercise supports brain health and contributes to our overall well-being—whether we’re facing anxiety, addiction, depression, or simply the desire to grow and learn, exercise helps.

In this final section of the guide we’ll look at the recommendations Ratey offers for building exercise into our life routines.

We’ll see:

• What form of exercise is best for reaping the benefits Ratey explores
• What your maximum heart rate is and how to use it to determine your most effective workout
• Some ideas for incorporating exercise into your daily routine

Aerobic Exercise Is Best

Ratey argues that not all forms of exercise are equally effective for optimizing brain function. Studies show that aerobic exercise is best. This isn’t to say that other forms of exercise aren’t beneficial, it’s just that aerobic exercise is currently understood to be optimal for tapping into the benefits we’ve explored.

(Shortform note: Researchers have demonstrated that both endurance exercise (e.g. running) and resistance exercise (e.g. weight lifting) increased the release of factors such as brain-derived neurotrophic factor and insulin-like growth factor. These proteins are critical for strengthening the neural network and reversing cell deterioration. This more up-to-date information suggests that resistance exercise should be included in your exercise routines.)

The benefits of exercise are distributed among three zones of intensity—the more powerful the workout, the more powerful the body’s response. We’ll take a look at how you can determine the intensity of your workout in the following subsection on heart rate.

• Low-intensity exercises are the baseline. At this level, your body begins releasing the neurotransmitters and factors we’ve discussed, and your body starts improving its metabolic function by burning fat. This helps to restore, maintain, and improve your brain’s function, setting the groundwork for more intense exercise.
• Medium-intensity exercise ramps up these processes and initiates more. At this intensity level, your body is exposed to a good amount of useful stress—the kind that builds resilience in your brain’s systems. New blood vessels are built, the process of neurogenesis is encouraged, your body’s stress response is conditioned and relaxed, and endocannabinoids are released.
• High-intensity workouts are powerful and must be handled with care. At this level, your body can reach a point where it becomes oxygen-deprived and your metabolism enters an anaerobic state. You feel this as muscle burn. Too much time in this state can be damaging for the body, but in moderate doses, it can be extremely beneficial. Accordingly, when you’re in the middle of a high-intensity workout, it’s best to stay just below this point most of the time and occasionally pass it.

(Shortform note: In Awaken the Giant Within, Tony Robbins suggests that you build a routine of exercise first on moderate-intensity aerobic exercise for a period of two to eight months. Laying the groundwork here, he suggests, will prepare you for engaging in more high-intensity anaerobic exercise.)

A reliable description of the sweet spot for a high-intensity workout is when the exercise feels “somewhat hard.” In addition to all the other effects we’ve discussed, during such a workout the body begins releasing human growth hormone (HGH), which burns fat, increases muscle growth, and grows your brain.

Human Growth Hormone Isn’t Always Good

Ratey doesn’t note the fact that human growth hormone (HGH or GH) is damaging to the body in high amounts. This isn’t a relevant risk for most people who get their HGH via exercise, but HGH is also prescribed as a pharmaceutical to reverse muscle loss, reduce fat, strengthen bones, and provide energy.

In most cases, a legitimate doctor’s prescription is judicious and directly effective for treating symptoms of a disease. However, the illicit use of HGH—often sought as a “fountain of youth” drug (a phrase Ratey refers to)—can have serious negative consequences, including heart disease, diabetes, and a shorter life span.

Ratey is careful to remind his readers that doing something is better than doing nothing. Don’t get discouraged if you can’t reach or maintain a high-intensity workout yet. As we’ve seen all along the way, the brain is optimized for movement, so the key is to move.

World Health Organization Guidelines on Physical Activity

The World Health Organization (WHO) echoes Ratey’s sentiment that doing something is better than doing nothing. According to the WHO, a lack of physical activity is a leading contributor to global mortality: They estimate that, as of 2016, nearly a third of all adults and four-fifths of adolescents were not active enough. Physical inactivity is known to increase the risk of heart disease, diabetes, and cancer, in addition to shortening lifespan.

The WHO recommends that adults aged 18 to 64 should get at least 150 to 300 minutes of moderate physical activity during the week. Children and adolescents should get at least 60 minutes per day of moderate to vigorous physical activity.

Determining Your Heart Rate

Because individual fitness levels vary, an exercise that’s intense for one person won’t be intense for another. You can determine the intensity of your workout by measuring your heart rate—the faster your heart is beating, the harder you’re working.

The first step is determining your maximum heart rate—the hardest your heart can work. This varies according to your age and overall health, but Ratey shares a rule of thumb for calculating it: Subtract your current age from 220. The intensity of your exercise is determined as a percentage of that maximum rate. The higher the percentage, the more intense the workout. This is simply calculated by multiplying your maximum heart rate by a decimal equivalent to the percentage you’re looking to achieve.

Let’s look at walking, jogging, and running as templates for intensity. Keep in mind that other forms of aerobic exercise can put your heart rate into these different zones (for example, jumping rope or cycling).

• Walking should put your heart rate between 55% and 65% of your maximum. This is considered low intensity.
• Jogging is 65% to 75%. This is medium intensity.
• Running is 75% to 90%. This is high intensity.

Monitoring Your Heart Rate With a Smartwatch

In Spark, Ratey encourages his readers to buy and use a heart rate monitor to track the intensity of their exercise. In general, these consist of a chest band sensor and a digital receiver of some kind (for example, a watch) that displays a reading.

In the time since Spark was published, new technologies have made monitoring your heart rate even easier. Smartwatches are now typically equipped with heart rate monitors that are generally accurate for tracking your heart rate during exercise. Current readers of the book will likely be inclined to use a smartwatch. While this is generally fine, it’s important to be aware of caveats about their use in order to get the best information possible.

Some experts have pointed out some of the shortcomings of the general smartwatch’s ability to give accurate data about your heart rate. They note that the typical sensors used in smartwatches have a higher error rate when used on darker skin or by those with a higher body mass index and their position on the wrist can lead to inaccurate readings. Bearing these facts in mind, with a little care and cross-checking, smartwatches can be helpful for ensuring your exercise is at the right intensity.

Making Exercise Stick

Determining the best way to get exercise into your life is a personal decision. With that said, there are several tips Ratey suggests throughout Spark that may help augment its effectiveness and make it stick.

Do something you enjoy.

This may sound simple, but if you enjoy riding a bike and despise running, then ride a bike. The more you enjoy it, the more likely you are to do it.

Try new things.

Variety can keep it interesting, and interest can go a long way toward keeping you at it. So go ahead and learn a new skill or try a new routine. You may discover other forms of exercise you like.

Do it with others.

Humans aren’t only built for movement, they’re also built for social interaction. Exercising with others encourages accountability and magnifies the neurochemical effects of the workout–and it can make it more fun.

Exercise Isn’t for Everyone

These first three recommendations are mainly designed to help you enjoy exercise, which some experts have identified as a crucial factor in how beneficial exercise might be.

Neuroscientist Elizabeth Gould believes this. She has played an instrumental role in researching adult neurogenesis and is responsible for some key discoveries in the field.

For instance, she has found that rewarding experiences affect neurogenesis and cell survival: Activities such as mating and running enhance neurogenesis in rats, and stressful experiences reduce it. While rats enjoy running, many humans don’t. As she sees it, if exercise isn’t a rewarding experience for some people it may not confer neurological benefits to them.

Scientists have found that some people are genetically predisposed to enjoy exercise and others are not—a significant implication of this is that some people may have a hard time reaping the neurological benefits of exercise.

Thus, while there’s ample evidence to suggest that exercise is beneficial for the brain, it’s not clear that those findings are complete—a person's enjoyment of exercise, either because of genetics or because of recommendations like these above, might affect how beneficial it is, and mean that not everyone may reap the psychological benefits Ratey discusses.

Keep at it.

Sometimes the best way to stick to a routine is to simply remind yourself that you can’t afford not to. When it comes to your mind and exercising, just remember that your body was built to move—it needs to move. So, whatever you do, keep it up. Don’t berate yourself if you miss a day or two, just get back to it as soon as you can.

(Shortform note: Some experts offer other tips for sticking to an exercise routine that can help you keep at it even when you don’t want to. For instance, they recommend that you set small goals for yourself, make charts of your progress, and give yourself meaningful rewards for achieving your goals.)