Exercise is one of those topics, along with diet, that generates a lot of confusion. And while there is no shortage of advice to be found online, it is rarely based on our best science or on our understanding of the intricacies of human physiology, evolution, and anthropology. 

In Exercised, Harvard professor of evolutionary biology Daniel Lieberman explains that to truly understand exercise science, you must first understand something about human evolution and anthropology and how the body evolved to handle exercise. As Lieberman wrote, “nothing about the biology of exercise makes sense except in the light of evolution, and nothing about exercise as a behavior makes sense except in the light of anthropology.” 

Using this evolutionary/anthropological framework, Lieberman sets out to explain how the body works when at rest (sitting and sleeping), when active (walking, running, lifting, fighting, dancing), and what this means for establishing effective exercise habits in the modern world. Far from being a self-help book or a simple guide to developing an exercise routine, Exercised helps you to understand why exercise is good for you and the science behind when, how, and what types of exercises you should be pursuing, dispelling several myths about exercise along the way. 

The first—and most fundamental—myth is that we evolved to exercise. The truth is the opposite, and there are good evolutionary reasons for why most people wish to avoid it. (Note that by “exercise” Lieberman means voluntary physical activity pursued for no other purpose than to promote health and fitness.)

The first thing to understand is that humans spent most of their 200,000-year evolutionary history as hunter-gatherers, with the invention of agriculture occurring only around 10,000 years ago and the modern industrial revolution beginning only about 200 years ago. The key to understanding our relationship to exercise, therefore, is found in the study of these hunter-gatherer groups. 

As Lieberman explains, modern hunter-gatherer tribes (including the Hadza) are puzzled by any mention of exercise, or voluntary activity with no purpose other than the promotion of health. Because hunter-gatherers spend hours each day sourcing food, they tend to spend the remainder of the day conserving energy. 

You find the same behavior in apes, our closest evolutionary cousins, and in all other animals. Energy is expended on obtaining food, survival, and reproduction, with periods of rest in between. Since every calorie expended in nature counts, it would make no sense to expend needless energy on any activity that does not enhance reproductive fitness. 

What’s unique about modern post-industrial humans is that we’ve flipped this logic on its head. Because most of our jobs are now sedentary and we’re surrounded by labor-saving devices, we have to engage in physical activity for no other purpose. This is both unprecedented in the animal kingdom and in most of our own evolutionary past. There is little wonder, then, that most people lack the motivation to work out. 

That’s the bad news. The good news is that it would take less exercise than you might think for the modern sedentary Westerner to match the energy expenditure levels of a hunter-gatherer. This is because your resting metabolic rate (RMR) (the daily energy required to sustain your body at rest) represents about two-thirds of your energy requirements. If you’re an average adult male that weighs 180 pounds, your RMR is about 1,700 calories, while your total daily energy expenditure (DEE) is approximately 2,700 calories. 

The upshot is that, since both you and a hunter-gather expend most of your energy at rest—and because hunter-gatherers are also sedentary when not sourcing food—“it would take you just an hour or two of walking per day to be as physically active as a hunter-gatherer,” as Lieberman writes. This both eliminates the stigma associated with not wanting to exercise and demonstrates that it doesn’t take all that much effort to get the appropriate amount of exercise—even for those with sedentary lifestyles.

Having outlined our evolutionary aversion to exercise, Lieberman proceeds to explain the physiology and biomechanics of a host of physical activities, dedicating each chapter to one activity or function (walking, running, weight training, etc.). Each chapter provides insightful and fascinating information, but the focus on debunking myths often feels forced and tedious. 

Lieberman decides to open each chapter with a myth, but the reader is left wondering just how prevalent these “myths” really are. Myth #6, for example, is the belief that we evolved to be extremely strong, but you might wonder how common this belief really is. Lieberman’s tendency to present all of his ideas as profoundly opposite of conventional wisdom gets tiresome fast.  

Here’s another example: “Myth” #8, which is the belief that you can’t lose weight by walking, seems to be largely true and not a myth at all. As Leiberman himself writes: 

“It bears repeating that if I power walk five miles, I’ll expend roughly 250 extra calories, as many calories as I’ll acquire from snacking on the granola bar in my backpack.”

If walking five miles equals the calorie content of a granola bar—and walking those five miles makes you hungrier and more likely to eat that granola bar—then that tells me that it is significantly easier to lose weight through diet than exercise, and that it is unlikely that walking is going to result in substantial weight loss over a reasonable amount of time. While there are several benefits associated with walking, weight loss is unlikely to be one of them (without the appropriate diet).

Yes, you can lose weight by walking, but it would be (1) very slow, (2) very time-consuming and inefficient, and (3) impossible without resisting the urge to consume more calories after expending the extra energy. So when you hear that you can’t lose weight by walking, while that statement is not entirely true, I wouldn’t call it a myth either. And this is my biggest problem with the presentation overall; it encourages black-and-white thinking even when the reader probably wasn’t thinking in those terms to begin with. To be fair, Lieberman does present the full complexity of the issues, but I felt that the focus on dispelling myths in every chapter was forced and unnecessary. 

In the final part of the book, Lieberman again reminds us that we did not evolve to exercise. Our ancestors engaged in physical activity out of necessity (survival and reproduction) or pleasure (games, dancing, etc.), but never for the purpose of promoting health and fitness. We are therefore evolutionarily programmed to avoid wasting energy on unnecessary activities.

At the same time, Lieberman also reminds us that because most of our lives are now relatively sedentary, we do require exercise to stay healthy, as study after study demonstrates the various mental, physical, anti-aging, and disease-prevention benefits of exercise. As recommended by several health agencies, a good rule of thumb for adults is a minimum of 150 minutes per week (30 minutes a day for five days) of moderate aerobic exercise with two supplemental sessions involving weights.   

So how can we get ourselves to exercise more? According to Lieberman, because exercise is optional, and, for most people, unpleasant, we should adopt strategies that make exercise either mandatory or more fun. Lieberman recommends things like listening to music or podcasts while working out, working out with friends, exercising outdoors, instituting variety into our routines, rewarding ourselves, and various suggestions for making exercise mandatory through commitments to friends or organizations (physical activity has always had a strong social component for humans). 

His most profound recommendation—one that has the potential for the largest impact on society—is expanded mandatory physical education in K-12 and college education. As Liberman wrote:

“In one study, 85 percent of students who exercised regularly in college continued to exercise later in life, but 81 percent of those who were physically inactive in college remained sedentary as older adults.”

Compare this with the fact that most universities have dropped their physical education/activity requirements altogether. In fact, it is estimated that only a quarter of college students get baseline levels of regular exercise despite high levels of depression and anxiety, and despite the fact that studies suggest that exercise can treat depression and anxiety as well as or better than medication or therapy.

Additionally, only 11 percent of elementary school districts have physical activity breaks during the school day, and that number drops to 2 percent for high schools. By encouraging inactivity, we are training our kids to establish habits of inactivity that last the rest of their lives—all to prioritize standardized testing and academics (even when exercise has been shown to improve cognition and memory).

According to the CDC, only 23 percent of all US adults get the recommended 150 hours per week of exercise. For children ages 6 to 17, less than 24 percent get the recommended 60 minutes of physical activity every day. Not only is this unhealthy in the short term, it sets up lifelong habits of inactivity that increase the risk of developing various diseases including heart disease, diabetes, stroke, and more (some of the leading causes of death in the US). I’d say it’s about time we start reassessing our priorities. 

Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding is available on Amazon.com.

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