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

by Daniel E. Lieberman

Incessant sitting combined with modern diets and other novelties thus contributes to evolutionary mismatches, defined as conditions that are more common and severe today than in the past because our bodies are poorly adapted to novel environmental conditions.3

What Is the Hypothesized Mismatch?

If mismatches are caused by harmful interactions between genes and environments in which environments rather than genes recently changed, it’s hard to find a bigger example than obesity.

A two-mile walk burns about 100 more calories than sitting, but that refreshing Coca-Cola afterward contains 140 calories.

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.10

Even better is to avoid both risk factors: nurses who are lean and fit have 2.4 times lower mortality rates than those who are obese and unfit.

How Much and What Kind of Exercise Are Best?

This one is easy: cardio is better than weights for obesity.

Metabolic Syndrome and Type 2 Diabetes

Metabolic syndrome and type 2 diabetes are unambiguous mismatch conditions. They are essentially unrecorded among hunter-gatherers, rare among subsistence farmers, and only recently have become epidemic.16

Because too much sugar is toxic to many cells, excess sugar stimulates your pancreas to release the hormone insulin, whose basic function is to cause the body to store energy.

Eventually, the overworked pancreas fails, requiring injections of insulin to avoid death.

In one compelling study, Danish researchers randomized patients with type 2 diabetes into two groups: both were given advice on how to eat a healthy diet, but one group also labored through five or six 30- to 60-minute-long sessions of aerobic exercise a week plus two or three weight sessions per week. After a year, half of those who exercised were able to eliminate their diabetes medications, and another 20 percent were able to reduce their medication levels. Further, the more they exercised, the more they recovered normal function. In contrast, just one-quarter of the dieters were able to reduce their medication, and 40 percent had to increase their medication levels despite receiving excellent, standard health care.24

Like the pipes in a building, arteries are vulnerable to getting clogged with unwanted deposits. This hardening of the arteries, termed atherosclerosis, starts with the buildup of plaque—a gloppy mixture of fat, cholesterol, and calcium—within the walls of arteries.

The average blood pressure in a seventy-year-old San hunter-gatherer is 120/67, no different from a twenty-year-old.

Cholesterol.

Your liver produces these balloon-like molecules to transport fats and cholesterol throughout your bloodstream, but some LDLs have a harmful tendency to burrow into the walls of arteries, especially when blood pressure is high.

The second type of cholesterol is high-density lipoprotein (HDL), sometimes called good cholesterol, because these molecules scavenge and return LDLs back to the liver.

The third type are triglycerides, fat molecules that are floating freely in the bloodstream and a sig...

Blood pressure.

the higher (systolic) number is the pressure your heart’s main chamber overcomes when it squeezes blood throughout your body;

the lower (diastolic) number is the pressure your heart experiences as its main c...

By convention high blood pressure is a reading greater tha...

Inflammation.

Plaques don’t form out of the blue but instead occur when white blood cells in the bloodstream react to the inflammation caused by LDLs and high blood pressure.

It is widely recognized that cardio exercise is best for the cardiovascular system. 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.

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

This evolutionary arms race has been going on for hundreds of millions of years,

but ever since the origins of agriculture, humans have made ourselves vastly more vulnerable to contagious diseases like cholera, smallpox, and RTIs that are passed from one person to another.

The fatigue we experience when fighting a cold is a reminder that the immune system is often energetically costly.

According to this idea, long-term physical inactivity depresses immune competence, moderate levels boost the immune system, and very high doses of physical activity temporarily compromise immune function, thus increasing vulnerability to infection, especially in unfit individuals.60

Chronic Musculoskeletal Conditions

Age is infamously unkind to muscles, bones, and joints. Among those fortunate enough to reach old age, it is not uncommon to be disabled by a trio of infirmities: muscle wasting (sarcopenia), bone loss (osteoporosis), and cartilage degeneration in joints (osteoarthritis).

Sarcopenia is the most obvious beneficiary of exercise.

Osteoporosis is a more complicated disease of disuse only partly prevented by exercise.

In particular, weight-bearing activities that load the skeleton cause bone-growing cells to add more bone when we are young, and they prevent bone-resorbing cells from removing bone as we age.78 Consequently, lifelong weight-bearing exercise helps prevent the disease.

Osteoarthritis is an enigmatic and poorly understood musculoskeletal disease despite afflicting millions of older people in industrialized countries.

Because muscles, bones, and joints primarily function to generate and withstand forces, they maintain and repair themselves principally in response to high forces.

Muscles benefit from all physical activities, but they respond most strongly to weight-bearing activities that require them to contract forcefully without changing length (isometric contractions) or as they lengthen (eccentric contractions). To prevent sarcopenia, do weights.

Bones also need weight-bearing exercises that apply forces of sufficient magnitude and rate to activate bone cells. Some of these forces occur from sudden impacts like a runner’s body hitting the ground, but muscles generally create the highest forces.81 Thus activities like jumping, running, and weight lifting that place demanding loads on bones help develop and maintain a strong skeleton much more than lower-impact activities like swimming or using an elliptical.82

Cartilage degeneration is probably countered by physical activity, but it is unknown how and to what extent different kinds of e...

Probably, the biggest benefit of physical activity is to prevent and reduce obesity, thus limiting inflammation as well as abnormally high pressures.83 Regular loading from activities like walking and maybe even running might als...

Cancer

Cancer scares me more than any other disease. Now the second-leading cause of death worldwide (killing about one in four), cancer is a sort of cellular Russian roulette that seems to strike indiscriminately, most often after the age of fifty.

but right now we need to pay more attention to preventing cancer.

According to one estimate, three to four hours of moderate exercise a week is likely to reduce a woman’s risk of breast cancer by 30 to 40 percent, and both men’s and women’s risk of colon cancer by 40 to 50 percent.94

High levels of physical activity divert energy from cancerous cells in at least four possible ways.

(1) Reproductive hormones. Energy spent on physical activity is energy not spent on reproduction, a trade-off modulated by reproductive hormones like estrogen.

(2) Sugar. Some cancer cells have a sweet tooth. In fact, many cancer cells tend to get their energy directly from sugars, which they burn anaerobically without oxygen.

(3) Inflammation. Inflammation, which goes hand in hand with chronic positive energy balance and obesity, is a risk factor for many cancers.