Physical exercise is HUGELY important for both your physical and mental health. This books focuses mostly on the mental side and just from the table of contents of the book we see the wide variety of problems where exercise can help:

  1. Learning
  2. Stress
  3. Anxiety
  4. Depression
  5. Addiction
  6. Hormonal changes
  7. Ageing

While the book focuses on the effects of exercise on the "bad" versions of this problems, it is clear that if exercise can help in the worst cases it can also help in the sub-clinical cases of feeling a bit stressed or sad in our day to day lives.


The book begins by describing the fascinating experiment "Zero Hour PE" carried out to the West of Chicago, in Naperville District 203, involving 19000 students in 2003.

Students were free to come to school one hour earlier than usual and spend that hour exercising. They performed fitness activities such as running rather than team sports, where there can be a lot of waiting around and a much more diluted exercise.

In order to motivate people with bad athleticism genetics, the grading was based on effort rather than absolute goals, by using the at the time futuristic technology of heart rate monitors. The kids where graded based on how much time they stayed in their target heart rate zone. An extremely important feature necessary to make the habit of training more likely to stick for life is to give a wide variety of possible sports to kids, in order to allow them to find something they are good at and associate it with a feeling of proficiency and mastery.

The program brought a slight improvement in the students grades with respect to the control group with 17% improvement for kids participating in the program versus a 10.7% improvement for kids not participating. Think about the massive effect of this change compounded for 10 years of education. We must also remember that the alternative was sleeping, and, considering how often teenagers are sleep-deprived, I would expect that removing an hour of sleep would bring about a substantial decline of academic performance, so, given that here we see the opposite, in my opinion the effect of exercise is quite larger than 6.3%.

But life is not all about books and learning, avoiding jail is also really good. At Woodland Elementary School in Kansas City, expanding PE class from once a week to 5 times a week with a focus on cardiovascular fitness decreased the number of violent incidents from 228 to 95 for the year. Of course we are talking about little children and it is normal for them to fight a little, but, in my opinion, growing up in a violent environment can easily set-up a negative feedback loop of becoming antisocial and being violent yourself and making it more likely both for yourself and your peers to take the wrong path later in life. Releasing the pent-up energy in a productive manner through exercise is very beneficial.

The book holds the thesis that exercise creates BDNF (Brain Derived Neurotrophic Factor) that improves learning by facilitating the creation of new connections, this is outside my area of expertise but I will just underline that in a 2007 study on humans, researchers found that participants learned new words after exercise 20% faster than participants that did not exercise and the rate of learning was linearly correlated with BDNF (Brain Derived Neurotrophic Factor) in the brain, pointing in the direction that this is not just placebo but there is some real chemical effect happening under the hood.


Stress is a threat to the body's equilibrium, a challenge to react and adapt to a new stimulus. Exercise is clearly a form of stress under this definition, with muscles having to repair after being slightly damaged by exercising, the point is that the stress induced by exercise is fully voluntary and adjustable to a challenging but not damaging level. Metaphorically we are inoculating the brain with a small stress to make it better at handling the bigger stresses of life, like a vaccine would inoculate the immune system with a dead virus to make it better at fighting a live one.

On a shorter time-scale, when faced with imminent danger the fight-or-flight response gets activated, a quite complicated cascade of chemical signals leaving you alert and ready to move yourself to get out of that sticky situation. The problem is that in the modern age we have a very strong response, that for other animals can only be had in life or death situations, even for events where the potential loss is tiny when compared to death (e.g. an exam, a job interview). Furthermore, we do not literally need to fight or escape in such situations, the task required is often mental and performed while sitting perfectly still.

Cortisol, the "stress chemical" released during the fight-or-flight response would "normally" (in an ancestral environment when you actually had to run away) get cleared after you put some distance between yourself and the threat and the exercise you did running away would kick-start the cellular recovery process to fix the damage caused by stress. This cycle gets broken in modern life with obligations from work following you at home and a lack of physical exercise. While you probably cannot (or do not want to) stop working, running or doing some aerobic activity after work or a hard job interview or exam will greatly reduce stress. 



Brain scans of people with anxiety disorders show that the area of the prefrontal cortex tasked with stopping the amygdala from giving out fear signals is smaller than in healthy people. Also mice with a gene variation that inhibits the action of BDNF do not get relief from fear given by a scary situation when given Prozac. The book speculates that the BDNF produced during exercise helps the brain form new connections and reduce anxiety (the speculation is about the biological mechanism, the effect of exercise against anxiety has been shown to be there by scientific studies).

In 1997 German psychiatrist Andreas Brooks a ten week trial on 46 patients suffering from panic attacks divided in 3 groups: exercise, clomipramine and placebo. While at the start everyone improved (including placebo), at the end the placebo group got its symptoms back while the clomipramine and exercise had a similar level of improvement.


Depression & Addiction

I grouped this together, because the culprit of these problems is the constant feeling of emptiness. The life of an addict is in very large part dedicated to getting more of the drug, and everything else gets sacrificed, financial stability, family and friends. When the addict tries quitting he must find a way to productively employ the time he previously used trying to get and use the drug. The same can be said for the depression, but the feeling of weakness and emptiness is more generalized and grows with negative feedback loop, when feeling weak and unmotivated you do nothing interesting, getting weaker and less motivated and doing even less and so on and so forth. So the cure for these conditions is exercise! A productive way to spend time becoming stronger and filling in the many hours used destructively either self-commiserating or trying to find and abuse drugs. Exercise also provides the patient with the feeling that he defeated depression/addiction with his own efforts, and that his success was not gifted to him by a medication, improving self-esteem.

As far as depression is concerned, exercise is at least as good as antidepressants and probably much better: in the SMILE study of James Alan Blumenthal at Duke university, 156 patients were randomly assigned exercise, Zoloft or both to treat depression, about half of each group was completely cured of depression. After 6 months only 30% percent of the exercise group remained depressed versus 52% of the medication group and 55% of the group doing both (yes this result is very weird, patients said that the medicine was taking away their pride of defeating depression by working hard with exercising). The relapse rate was 8% in the exercise group versus 38% in the medication group.

Hormonal changes

Exercise has large positive effect on both Premenstrual syndrome and Post Partum Depression. The American College of Obstetricians and Gynecologist suggests at least 30 minutes per day of moderate aerobic exercise for pregnant women, and despite this 23% of women stop exercising when they become pregnant on the false preconception that the dangers outweigh the benefits (I am not a doctor, if you are pregnant ask a doctor to consider benefits and risks of your specific exercise regime given your specific situation). A very small study on 34 women of James Clapp, professor at Case Western Reserve University shows that exercise during pregnancy might improve the health of the newborn.


After some anecdotes and a very general description of the process of aging, the book gives a quite impressive list of the benefit of exercise, especially for slowing down aging:

  1. It strengthens the cardiovascular system
  2. It regulates glucose, a risk factor for Alzheimer's
  3. It reduces obesity
  4. It elevates the stress threshold, so the cells will self repair better
  5. It lifts the mood
  6. It boosts the immune system
  7. It fortifies the bones
  8. It boost motivation, that can be lacking in old age


Exercising (two 60 seconds uphill sprints per day on the bicycle + around 60 minutes of very low intensity pedaling) radically changed my mood and general outlook on life in just a few weeks. I have since stopped that particular kind of exercise but I feel like the benefits persisted.

I could have gone more in depth with my book review but my objective is not filling the poor readers with medical jargon. The evidence that exercise is largely beneficial to both your physical and mental health is rock solid, and, while you, the dear reader, hopefully do not suffer from any of these problems we should always strive to become happier and live longer and better. Tsuyoku Naritai! I want to become stronger! If you are convinced by this review I suggest that you confirm this with appropriate further research and that you take your ideas seriously and start exercising, no procrastinating, there is no need to wait for tomorrow, start today.

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2 comments, sorted by Click to highlight new comments since: Today at 4:34 PM

Thanks for writing this!

Something you might want to consider in the future is going into the claims made by the book slightly more. While I was reading this, I found myself constantly thinking "Yeah, but should I trust this study?". It sounds like you've looked into this and find them convincing, but I personally would have found it useful to include a little bit more information, like "How big was the study?", "Was it observational or experimental?", "Has anyone reproduced the results?".

The part I was most skeptical of is:

Students were free to come to school one hour earlier than usual and spend that hour exercising. They performed fitness activities such as running rather than team sports, where there can be a lot of waiting around and a much more diluted exercise.

It sounds like there's a pretty major confounder here if group A is "kids who chose to go to school an hour earlier" and group B is "kids who chose not to go to school an hour earlier". I would be very surprised if group A didn't do better in school, given that they're being selected for motivation/not being tired/etc.

Anyway, I still found this useful and don't want to be negative; just thoughts on what would make it even better for me in the future.

Thanks for your feedback, in fact correlation is not causation and we must be very careful about self-selection effects. This is not a self-selection effect but still a correlation/causation enigma that I found interesting in recent times: high vitamin D levels were found to be heavily anticorrelated with severe COVID in observational studies, but people of old age are both sensible to severe COVID and have lower vitamin D than average, not only that but people with a healthy lifestyle of many outdoor walks also have higher vitamin D! Is this causation, correlation or both? There is a very interesting article about this on Astral Codex 10 (COVID/Vitamin D, Much More Than You Wanted To Know)