Exercised: The Science of Physical Activity, Rest and Health

by Daniel E. Lieberman

Along the same lines, it is possible that eating lots of carbohydrates during exercise diminishes the body’s anti-inflammatory response.

This kind of “no pain, no gain” philosophy has inspired a dizzying array of self-inflicted hardships thought to ward off aging (an added benefit is their aura of virtue).

Hoping to live longer, people take cold showers, restrict their caloric intake, endure long periods without eating, shun carbohydrates, burn their digestive tracts with spicy food, and more.53 Some of these strategies are downright questionable, and, with the exception of intermittent fasting, none is yet supported by solid evidence as a way to extend human longevity.54

So while physical activities trigger cycles of damage and restoration, selection favors individuals who allocate enough but not too much energy to producing antioxidants, ramping up the immune system, enlarging and repairing muscles, mending bones, and so on. The challenge is to maintain and repair any damage from physical activity just enough and in the right place and the right time.

Evolution’s stingy solution to this problem is to match capacity in response to demand. In this case, the demand is the stress caused by physical activity, especially reactive oxygen species and other damaging processes that stiffen arteries, mutate genes, and gunk up cells. The capacity is the ability to maintain, often through repair, a stable internal environment so we can adequately and effectively perform those functions needed for survival and reproduction.

And, crucially, the maintenance and repair mechanisms activated by physical activity don’t cease to function as we age. Although some become less responsive, they keep on ticking, allowing physically active po...

So just as our species never evolved to diet or cope with jet lag, we never evolved to counter many aging processes to the same degree without physical activity. Absence of regular physical activity thus becomes a mismatch condition as we age by allowing us to senesce faster.

The bad news is that despite impressive advances in preventing and treating infectious diseases, many people today get sick from chronic noninfectious diseases that involve many years of morbidity prior to death.

This shift, in which more of us live longer but die from chronic rather than infectious diseases, thus extending morbidity, is known as the epidemiological transition and widely hailed as medical progress.

By not dying rapidly from smallpox in our youth, aren’t we fortunate to die slowly from heart disease at an older age? This thinking is mistaken. My last book, The Story of the Human Body, made the case that many of the diseases that kill us slowly today are mismatch diseases caused by our bodies being imperfectly or inadequately adapted to modern environmental conditions like smoking, obesity, and physical inactivity.

FIGURE 28 How physical activity affects health span (morbidity) more than life span (mortality).

Simply put, an unhealthy lifestyle affects morbidity twice as much as mortality.

In a nutshell, persistent physical inactivity along with smoking and excess body fat are the biggest three factors that influence the likelihood and duration of the major illnesses that kill most people who live in industrial, westernized contexts.

In sum, running caused a compression of morbidity, thus also extending lives.

As Hippocrates would have predicted, scores of other studies on the effects of physical activity on morbidity and mortality yield similar results.61 That doesn’t mean, however, that physical activity is a surefire Fountain of Youth, and remember it doesn’t delay mortality by preventing aging per se. Instead, physical activity triggers a suite of mechanisms that increase the chances of staying healthy with age by retarding senescence and preventing many chronic diseases that contribute over time to mortality.

First, and most fundamentally, the mortality and morbidity statistics I have been citing are probabilities.

Second, advances in medical care are shifting the relationship between morbidity and mortality.

Finally, many complex environmental and genetic factors contribute to the probability of getting a disease, making it difficult to unravel causation.

In these and other cases, genes help load the gun, but environment pulls the trigger.

We evolved to be physically active as we age, and in turn being active helps us age well. Further, the longer we stay active, the greater the benefit, and it is almost never too late to benefit from getting fit. People who decide to turn over a new leaf and get fit after the age of sixty significantly reduce their mortality rate compared with others who remain sedentary.67

For most of us, however, the problem is not recognizing the benefits of physical activity but overcoming natural disinclinations to exercise at any age and figuring out how much and what kind of exercise to do.

The routine brought to mind the running guru George Sheehan’s observation that “exercise is done against one’s wishes and maintained only because the alternative is worse.”

The resulting paradox is that our bodies never evolved to function optimally without lifelong physical activity but our minds never evolved to get us moving unless it is necessary, pleasurable, or otherwise rewarding.

Henrik says he wants his employees to exercise because he wants them—and by extension his company—to be the best people they can be, and that requires exercise. It’s why, like Quiet Hour and other unusual aspects of Björn Borg culture, Sports Hour is compulsory.

Exercise, moreover, is part of a general fitness culture at Björn Borg. Instead of a boozy Christmas party, the entire company goes sledding and then drinks hot chocolate. Every summer they do a six-mile “fun run” through the streets of Stockholm.

Libertarian paternalists favor nudges over coercion. Instead of forcing people to exercise, libertarian paternalists provide incentives.

And maybe you have been striving unsuccessfully to get yourself

and studies of humans suggest that some of us inherited tendencies to be slightly less inclined to exercise.

The good news is that some of these interventions can and do make a difference.

Comprehensive reviews that have examined hundreds of high-quality studies find that many interventions fail, and those that succeed tend to have only similarly modest effects.

Indeed, studies that try to figure out who does and doesn’t regularly exercise find few factors common to exercisers apart from some really obvious ones: having a prior history of exercising, being healthy and not overweight, having confidence in the ability to exercise, being more educated, and both liking and wanting to exercise.

Like it or not, little voices in our brains help us avoid physical activity when it is neither necessary nor fun.

First, necessity. Everyone, including the billion or so humans who regularly don’t get enough exercise, knows that more exercise would be good for them.

In addition to being unnecessary, exercise takes precious time, keeping us from other, higher-priority activities.

Which brings up fun. Lack of time can be stressful, but even the busiest people I know manage to find time to do things they enjoy or find rewarding like watch TV, surf the web, or gossip. I suspect millions of non-exercisers would succeed in making exercise a greater priority if they found it more enjoyable, but for them exercise is often emotionally unrewarding and physically unpleasant.

Like most organisms, we have been selected to enjoy and desire sex, eating, and other behaviors that benefit our reproductive success and to dislike behaviors like fasting that don’t help us have more babies.

Peer pressure is a powerful motivator.

Because exercise by definition isn’t necessary, we mostly do it for emotional or physical rewards,

So when friends or CrossFitters work out together in the gym, teams play a friendly game of soccer, or several people chat for mile after mile as they walk or run, they are continuing a long tradition of social physical activity.

As a result, we have been selected to enjoy doing activities in groups, to assist one another, and to care what others think of us.

A solitary walk or run can be meditative, and working out while listening to podcasts or watching TV in the gym (a distinctly modern phenomenon) can be diverting. But for most people exercising with others is more emotionally rewarding.

Exercise can also make us feel good, which helps make it enjoyable. After a good workout I feel simultaneously alert, euphoric, tranquil, and free from pain—not unlike taking an opioid. Actually, natural selection did adopt this drug-pushing strategy by having our brains manufacture an impressive cocktail of mood-altering pharmaceuticals in response to physical activity.

Dopamine. This molecule is the linchpin of the brain’s reward system. It tells a region deep in the brain “do that again.” Evolution thus geared our brains to produce dopamine in response to behaviors that increase our reproductive success including having sex, eating delicious food, and—surprise—doing physical activity.

Serotonin. This still mysterious neurotransmitter helps us feel pleasure and control impulses, but it also affects memory, sleep, and other functions.

Elevated levels of serotonin induce a feeling of well-being (the drug ecstasy exaggerates this feeling by boosting serotonin levels sky-high), and we become better at controlling nonadaptive impulses.

Endorphins. Endorphins are natural opioids that help us tolerate the discomfort of exertion.

Although their effects can last for hours, endorphins aren’t produced until after twenty or more minutes of intense, vigorous activity, making them more rewarding for people who are already fit enough to work out that hard.

Endocannabinoids. For years, endorphins were thought to cause the infamous runner’s high, but it is now evident that endocannabinoids—the body’s natural version of marijuana’s active ingredient—play a much greater role in this phenomenon.

I suspect the runner’s high evolved primarily to increase sensory awareness to help hunters track animals during persistence hunting.

It’s a classic mismatch: because few of our ancestors were physically inactive and unfit, the brain’s hedonic response to exercise never evolved to work well in persistently sedentary individuals.