Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding

by Daniel E. Lieberman

exercise today is most commonly defined as voluntary physical activity undertaken for the sake of health and fitness.

And perhaps the most important similarity is that almost all the attendees were bystanders, not runners. While some of the spectators occasionally jumped into the race for a few laps, only a few Tarahumara compete in these races. Most are content to watch rather than run.

To keep going, great athletes must learn to cope with pain, be strategic, and above all believe they can do it.

we tend to think of ourselves and our societies as normal,

FAO scientists decided to measure people’s energy expenditures using the simplest metric possible, the physical activity level, or PAL.20 Your PAL is calculated as the ratio of how much energy you spend in a twenty-four-hour period divided by the amount of energy you would use to sustain your body if you never left your bed.

Here’s another, startling way of thinking about these numbers: if you are a typical person who barely exercises, it would take you just an hour or two of walking per day to be as physically active as a hunter-gatherer.

dictionaries generally define “exercise” as a “planned, structured physical activity to improve health, fitness, or physical skills,” and “play” as “an activity undertaken for no serious practical purpose.”

In sum, even if you are a highly active person, you probably spend more energy maintaining your body than doing stuff.

Effective diets, however, tend to be gradual, helping you lose weight slowly by burning just a little extra fat every day. A more demanding, hence revealing, stress test for your metabolism requires a more extreme reduction in energy intake: starvation.

The key lesson to digest from the starving men’s dramatically lower resting metabolic rates is that human resting metabolisms are flexible. Most critically, resting metabolism is what the body has opted to spend on maintenance, not what it needs to spend.

To appreciate trade-offs between inactivity and activity, it bears repeating that a calorie can be spent only once. In fact, as figure 3 illustrates, you can spend a given calorie in just five ways: growing your body, maintaining your body (resting metabolism), storing energy (as fat), being active, or reproducing.

Stated simply, we evolved to be as inactive as possible. Or to be more precise, our bodies were selected to spend enough but not too much energy on nonreproductive functions including physical activity.

Whether we take the stairs, jog, or go to the gym, we need to override ancient, powerful instincts to avoid unnecessary physical activity, and it should hardly be surprising that most of us—hunter-gatherers included—naturally avoid exercise.

There are three major, related health concerns about long periods of uninterrupted sitting. The first is what we are otherwise not doing. Every hour spent resting comfortably in a chair is an hour not spent exercising or actively doing things. The second concern is that long periods of uninterrupted inactivity harmfully elevate levels of sugar and fat in the bloodstream. Third and most alarmingly, hours of sitting may trigger our immune systems to attack our bodies through a process known as inflammation.

In healthy, normal human adults, including hunter-gatherers, fat constitutes about 10 to 25 percent of body weight in men and about 15 to 30 percent in women.

Put simply, regular movement, including getting up every once in a while, helps prevent chronic inflammation by keeping down postprandial levels of fat and sugar.

Even those who engaged in more than seven hours per week of moderate or vigorous exercise had a 50 percent higher risk of dying from cardiovascular disease if they otherwise sat a lot. Altogether, these and other alarming studies suggest that even if you are physically active and fit, the more time you spend sitting in a chair, the higher your risk of chronic illnesses linked to inflammation, including some forms of cancer.47 If these results are correct, then exercise alone doesn’t counter all the negative effects of sitting.

More truthfully, the problem isn’t sitting itself, but hours upon hours of inactive sitting combined with little to no exercise.

the best predictor of avoiding back pain is having a strong lower back with muscles that are more resistant to fatigue;

“Good posture is primarily a reflection of environment, habits, and mental state and is not a talisman against back pain.”

Calories come and go, but the arrow of time is inexorable.

It doesn’t take a lot of brainpower to realize that sleep is mostly about the brain. Over the last few decades, researchers have spent many sleepless nights to reveal how the neurological advantages of sleep outweigh its costs. One conspicuous benefit is cognitive: sleep helps us remember important things and helps synthesize and integrate them.

from an evolutionary perspective the only benefit of memory is to help us cope with the future.

One novelty of the modern world is our tendency to medicalize certain behaviors by prescribing them in specific doses.

Lack of sleep also wreaks havoc with the hormones that regulate appetite, increasing levels of a hormone called ghrelin that makes us hungry and simultaneously depressing levels of another hormone called leptin that inhibits the desire to eat.

Altogether, sleep deprivation helps promote obesity and its associated conditions like type 2 diabetes and heart disease; it is also associated with cancer.

several studies report that most of the benefits of sleeping pills are placebo effects.

we humans are slow, weak, vulnerable creatures more dependent on brains than brawn.

Although bipedalism has some benefits, it also came with drawbacks. In addition, to making us clumsy in trees, prone to tripping and falling, and more vulnerable to lower back pain, becoming two-legged made us perilously slow.

And therein lies an important reminder: even though the fastest humans have little chance of outrunning hyenas, to survive you sometimes need only be least slow.

But they work. If you keep up a regimen of two sessions a week of HIIT, your muscles will gradually improve their ability to produce high, rapid forces in part by augmenting how many fibers contract simultaneously when stimulated by nerves. In addition, your muscles will change composition. Although HIIT cannot stimulate your body to produce more fast-twitch muscle fibers, the ones you have will thicken, making you stronger and hence faster.

One potential drawback of bulking up too much is sacrificing power. Strength is how much force I can produce; power is how rapidly I produce it. Strength and power are not independent, but there is some trade-off between the two:

most of us are stronger than we think and never achieve our full potential because the nervous system sensibly inhibits us from going all out, thus tearing muscles, breaking bones, and possibly killing ourselves.

by intentionally shredding the muscle a little, you stimulate growth because the microdamage stimulates affected muscle cells to turn on a cascade of genes. Among other things, these genes augment the total number and thickness of muscle fibers, thus expanding the muscle’s diameter, making the muscle stronger.

As we age, muscle fibers typically dwindle in size and number, and nerves degenerate.50 The result is a loss of strength and power. On average, grip strength in industrialized countries like the United States and the U.K. declines about 25 percent from the age of twenty-five to seventy-five.

In fact, skill and attitude appear to be more important determinants of who wins than strength. As the combatants struggle, they must fight with their minds as much as their bodies to overcome pain and fatigue and figure out how to win.

Humans are endurance walkers.

Because life is fundamentally about acquiring and using scarce energy to make more life, those better able to conserve energy would have had a reproductive advantage.

Although far from easy, dieting is unquestionably more effective for shedding many pounds.

It bears repeating that the standard public health recommendation is 150 minutes of moderate exercise every week. This amounts to a paltry 21 minutes a day,

because walking is so energy efficient, it takes months or years for small doses of exercise to add up to substantial weight losses.

How could someone who spent five hundred extra calories a day exercising not have a total energy budget that is five hundred calories higher? The proposed explanation is that people’s total energy budgets are constrained: if I use five hundred extra calories walking, I’ll spend less energy on my resting metabolism to help pay for my exertions.

Known as "constrained energy expenditure hypothesis"

Finally, it truly is faster and it’s often easier to lose weight by dieting because everyone needs to eat but no one has to exercise, and not eating five hundred calories of energy-rich food (four slices of bacon) requires less time and effort than walking five miles a day.

Even more important, regardless of how one initially loses weight, keeping the weight off almost always demands physical activity.

Many experts, including some who study the Hadza, thus blame the obesity epidemic squarely on industrial diets, not activity levels.

We evolved to walk many miles a day in our strange, ungainly, upright, but efficient manner, and the fact that walking doesn’t expend a lot of calories is fundamental, not coincidental.

In essence, running is jumping from one leg to another.

As a shoe’s elasticity deteriorates, the built-in arch support loses effectiveness, putting extra strain on the plantar fascia.

Novice runners, especially first-time marathoners, risk injury because they can increase their mileage or speed (or both) faster than their shins, toe bones, Achilles tendons, IT bands, and other vulnerable tissues can adapt. Many experts thus advocate increasing mileage only 10 percent a week.

most experienced runners and coaches agree on four key, related elements illustrated in figure 25: (1) not overstriding, which means landing with your feet too far in front of your body; (2) taking about 170–180 steps a minute; (3) not leaning too much, especially at the waist; (4) landing with a nearly horizontal foot, thus avoiding a large, rapid impact force with the ground.