Exercised: The Science of Physical Activity, Rest and Health

by Daniel E. Lieberman

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.

The problem, of course, is that physical activity helps slow aging and promotes fitness and health. So those of us who no longer engage in physical labor to survive must now weirdly choose to engage in unnecessary physical activity for the sake of health and fitness. In other words, exercise.

Philosophers like Plato, Socrates, and Zeno of Citium preached that to live the best possible life, one should exercise not only one’s mind but also one’s body.

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.

If you are sitting while reading this, for every five breaths you take, one pays for your brain, another for your liver, a third for your muscles, and the last two pay for the rest of your body.

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.

Laziness, the disinclination to carry out an activity because of the effort involved, has become today’s version of sloth, but it shouldn’t carry the same spiritual overtones. Saving a few calories by parking in a prime location is hardly preventing me from fulfilling my duties to anyone. It’s just an instinct.

Rather than blame and shame each other for taking the escalator, we’d do better to recognize that our tendencies to avoid exertion are ancient instincts that make total sense from an evolutionary perspective.

Instead, the best predictor of avoiding back pain is having a strong lower back with muscles that are more resistant to fatigue; in turn, people with strong, fatigue-resistant backs are more likely to have better posture.

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

If, as some religions teach, we are made in God’s image, then God must be a slow runner.

Yet consensus isn’t truth.

The benefits of regular HIIT go well beyond its effect on muscles. Among other payoffs, HIIT increases the heart’s ability to pump blood efficiently by making its chambers larger and more elastic. HIIT also augments the number, size, and elasticity of arteries and increases the number of tiny capillaries that infuse muscles. HIIT further improves muscles’ ability to transport glucose from the bloodstream and increases the number of mitochondria within each muscle, thus supplying more energy.54 These and other adaptations lower blood pressure and help prevent heart disease, diabetes, and more.

bodies primarily sense if we are gaining or losing weight rather than how much excess fat we have. Whether you are skinny or stout, negative energy balance—including dieting—causes a starvation response that helps us restore energetic equilibrium or, better yet, gain weight so we can shunt more energy toward reproduction.35 It’s unfair, but losing ten pounds elicits food cravings and the desire to be inactive regardless of whether one is skinny or obese.

According to this theory, hardworking and helpful grandparents who looked out for others and who were blessed with genes that favored a long life had more children and grandchildren, thus passing on those genes.15 Over time, humans were evidently selected to live longer to be generous, useful grandparents.

many of the mechanisms that slow aging and extend life are turned on by physical activity, especially as we get older. Human health and longevity are thus extended both by and for physical activity.

the best advice for staying healthy as we age hasn’t changed in centuries: don’t smoke, avoid obesity, eat and drink sensibly, and of course stay physically active.

“exercise is done against one’s wishes and maintained only because the alternative is worse.”

For generation after generation, our ancestors young and old woke up each morning thankful to be alive and with no choice but to spend several hours walking, digging, and doing other physical activities to survive to the next day. Sometimes they also played or danced for enjoyment and social reasons. Otherwise, they generally steered clear of nonessential physical activities that divert energy from the only thing evolution really cares about: reproduction. 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.

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.12 That list of attributes is about as illuminating as figuring out that people who go to art museums tend to be people who already like art.

Be social: exercise with friends, a group, or a good, qualified trainer.27 Entertain yourself: listen to music, podcasts, or books, or watch a movie. Exercise outside in a beautiful environment. Dance or play sports and games. Because variety is enjoyable, experiment and mix things up. Choose realistic goals based on time, not performance, so you don’t set yourself up for disappointment. Reward yourself for exercising.

Every time I plan to exercise, I first struggle to prevail over instincts to not exercise. Afterward, I never regret it, but to overcome my inertia, I usually have to figure out how to make it seem necessary.

Exercise is no panacea, but the more you exercise, the longer you are likely to live, and the effects of physical activity on longevity become vastly greater as we age.

As my wife points out, the biggest risk of exercising too much is ruining your marriage, to which I would add that the biggest risk of exercising too little is not being around long enough to enjoy your marriage.

Putting it all together, I know gym rats who avoid cardio like the plague, and devotees of aerobics who wouldn’t touch a barbell if you paid them. Yet everyone benefits from mixing it up because weights, moderate-intensity aerobic exercise, and HIIT have different, complementary effects on the body.

Make exercise necessary and fun. Do mostly cardio, but also some weights. Some is better than none. Keep it up as you age.