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

by Daniel E. Lieberman

Because HIIT stresses the cardiovascular system more acutely than moderate-intensity aerobic exercise, it can yield rapid, dramatic benefits. Done properly, HIIT can substantially elevate aerobic and anaerobic fitness, bring down blood pressure, lower harmful cholesterol levels, burn fat, improve muscle function, and stimulate the production of

growth factors that help protect the brain (more on this in chapter 13).

If you regularly do the same thirty-minute leisurely jog or bike ride several times a week, consider adding a little HIIT to your weekly routine. (But please consult a doctor if you are thinking of trying this.) By some measures, a few minutes of HIIT provides as much benefit as, if not more benefit than, thirty minutes of conventional aerobic exercise, and it has the virtue of improving rather than just maintaining fitness. HIIT is also mercifully short-term, hence less tedious than hours of trudging. A quick HIIT session of sprinting, stair running, or whatever else you can manage is especially useful if you have little time to exercise.

But does this mean you should do only HIIT? I wouldn’t. HIIT done properly requires one to push really, really hard and is seriously uncomfortable as well as potentially inadvisable for individuals who are unfit or have health issues like joint pain or impaired cardiovascular function. In addition, it is unwise to do HIIT more than a few times per week, it doesn’t burn as many calories, and it may increase susceptibility to injury.

Most of all, it doesn’t deliver all the diverse benefits of regul...

All in all, HIIT is a faster way to improve fitness and a key complement to moderate aerobic exercise, but not the only way to get and stay in shape. Furthermore, as a form of intense cardio, many (but...

It bears repeating that when working against substantial loads, muscles can shorten (concentric contractions), but they are more stressed and grow larger and stronger in response to forceful contractions in which they stay the same length (isometric contractions) or stretch (eccentric contractions).

In the eighteenth century it was fashionable to lift church bells that were silenced (made “dumb”) by having their clappers removed, hence the term “dumbbells.”

As a result, every major medical health organization recommends we supplement cardio with weights, especially as we age. A consensus suggestion is two sessions per week of muscle-strengthening exercises involving all major muscle groups (legs, hips, back, core, shoulders, and arms).

Space these sessions several days apart to permit recovery, and they needn’t involve large weights but should include eight to twelve repetitions of

each exercise tiring enough to make you want to stop; two or three sets of exercises are mo...

I take my only exercise acting as a pallbearer at the funerals of my friends who exercise regularly. —Mark Twain

When we are young, physical activity prompts us to develop capacities like strong bones and improved memory; as we grow older, physical activity triggers many key maintenance and repair mechanisms that help us stay vigorous into middle and old age. And so, for countless generations, our ancestors rested as much as possible but also spent many hours a day walking, carrying, and digging, and occasionally they also ran, climbed, threw, danced, and fought. Their lives were challenging, and plenty of them died young, but physical activity helped many of those who survived childhood to become active, productive grandparents.

compendium

This calories-in-calories-out equation, however, is regulated by hormones, which in turn are strongly affected by diet and by other factors including psychosocial stress, the microbes in our gut, and, of course, physical activity.

question. Aside from overloading joints and interfering with breathing, excess fat cells overproduce hormones that alter metabolism, and when swollen, they become invaded by white blood cells that ignite chronic low-grade inflammation, damaging tissues throughout the body. Big deposits of enlarged fat cells in and around organs (so-called visceral, abdominal, or organ fat) are especially hazardous because they react sensitively to hormones and connect more directly to the bloodstream.

According to a few studies, individuals who become a little plump in old age (but not obese or extremely overweight) tend to live slightly longer, perhaps because they have more energy reserves to help them survive serious illnesses like pneumonia.

That is untrue. While overweight people who exercise and are physically fit lessen their risk of chronic disease, if you must choose between being fit and fat or unfit and lean, the evidence overwhelmingly indicates you should gamble on being unfit and lean.

Nurses’ Health Study, a

If so, obesity has nearly twice the effect on death rates as physical inactivity.

This one is easy: cardio is better than weights for obesity. As we will see later, weights help counteract some of the metabolic consequences of obesity, but cardio is better for preventing and reversing excess weight.

An astounding 20 to 25 percent of the world’s adults have metabolic syndrome, and that percentage is projected to double in coming decades.

Altogether, by simultaneously improving the delivery, transport, and use of blood sugar, exercise can resuscitate a once resistant muscle cell to suck up as much as fiftyfold more molecules of blood sugar. No drug is so potent.

Physicians and patients alike have been disappointed by the lackluster results of clinical trials that prescribed modest doses such as 150 minutes a week or less of walking.22 However, trials that prescribed more than 150 minutes a week of moderate-intensity exercise have

been more successful.

and more is better. As for exercise type, because metabolic syndrome and type 2 diabetes are so strongly linked to persistent positive energy balance, cardio remains the bedrock of most treatment plans.

If, however, you think plodding daily on a treadmill a form of torture, it’s heartening to know that you can and probably should mix it up. HIIT cardio is especially efficient and effective for countering metabolic syndrome.25

But atherosclerosis is by far the leading culprit, and chronically high blood pressure, hypertension, is a close second.

The average blood pressure in a seventy-year-old San hunter-gatherer is 120/67, no different from a twenty-year-old. Lifelong low blood pressure also characterizes many subsistence farming populations. My colleagues Rob Shave and Aaron Baggish and I measured more than a hundred Tarahumara farmers of every age and found no difference in blood pressure between teenagers and octogenarians.

Physical activity is also indispensable because the cardiovascular system never evolved to develop capacity and maintain itself in the absence of

demand. Inactivity thus makes us vulnerable to high blood pressure and heart disease.

It is widely recognized that cardio exercise is best for the ca...

Extended periods of aerobic physical activity require the heart to pump high volumes of blood to every corner of the body, stimulating beneficial responses that keep blood pressure low and the heart strong. Cardio also combats other risk factors for ca...

One massive study of nearly ten thousand men found that individuals with good cardiorespiratory fitness had more than a fourfold lower risk for cardiovascular diseases than those with poor fitness, and those who improved their fitness cut their risk in half.

As we have seen before, shorter doses of high-intensity cardio appear to be as good as if not more effective than lengthier doses of low-intensity cardio.44

While cardio unquestionably invigorates and strengthens the cardiovascular system, lifting weights also improves cholesterol levels (raising HDLs and lowering LDLs) and lowers resting blood pressure (although not as much as cardio).45 That said, doing only weights is apparently less protective than only cardio for the cardiovascular system.46

Thus, athletes who exclusively weight train without also doing some cardio appear to be at as much risk as sedentary individuals of developing chronic high blood pressure and cardiovascular disease.

Endurance athletes such as cross-country skiers had a stunning two-thirds lower risk of

heart attacks than average Finns, while power athletes like weight lifters and wrestlers had one-third higher rates of heart attacks.48

Bottom line: weight training isn’t bad, but don’t...

One possibility is that because heading off to the bush to hunt and gather potentially made our ancestors more likely to encounter pathogens, our immune systems evolved to compensate by ramping up our defenses when we are active.

These and other studies showing increased immune activity following moderate exercise but declines in white blood cell counts right after intense exercise have led to the hypothesis of a J-shaped relationship between exercise dose and immune function.

In particular, regular physical activity not only increases white blood cell counts but also appears to distribute preferentially certain cells from the bloodstream

to the places they are most needed, including the vulnerable mucus-covered linings of the respiratory tract and gut.61 Further, some of the most highly redeployed cells are those most effective at fighting viruses (these include natural killer cells and cytotoxic T cells).62 Studies that compare sedentary and active people

For these mice, a little exercise was better than none, but too much was deadly, highlighting the vital importance of rest when fighting a serious infection.

Fortunately, the mechanisms by which physical activity, especially weight-bearing tasks that generate resistance, maintains as well as reverses muscle atrophy remain effective with advancing age. Even octogenarians can bulk up in a gym.

Instead, we get osteoporosis only if we failed to develop enough peak bone mass when we were young, or if we lose bone too rapidly as we age.

One way to avoid osteoporosis is to develop as youngsters strong bones better able to withstand later losses. The other way to avoid the disease is to slow the rate of bone loss as we age. Age-related loss occurs in both men and women but is exacerbated

prevent bone-resorbing cells from removing bone as we age.78 Consequently, lifelong weight-bearing exercise helps prevent the disease.

But most cases of the disease appear to be influenced by inflammation triggered by obesity and possibly also physical inactivity.80