Exercised: The Science of Physical Activity, Rest and Health

by Daniel E. Lieberman

All things are poison and nothing is without poison; only the dose permits something not to be poisonous.

What does “best” even mean? Best in terms of how many years of life it adds? Best in terms of time efficiency? Best for preventing heart disease? Losing weight? Avoiding injury? Averting Alzheimer’s? Even if there were a way to choose a best plan for one of these goals, would the same plan be best for everyone regardless of age, sex, weight, fitness level, and history of injury?

the relationship between exercise dose and health is confusing.

terms of cardio, there are passionate advocates of running, walking ten thousand steps a day, swimming, or low-impact machines like ellipticals.

some prescribe using our own body weight, others recommend free weights, yet others push weight machines.

least 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity aerobic exercise per week, supplemented by two sessions of weights.

those who were over seventy and exercised the same amount had half the risk of dying in a given year as their inactive classmates.

dose-response relationship between exercise and mortality.

effects of physical activity on longevity become vastly ...

In 1995 and 1996, all three panels published essentially the same advice: to reduce the overall risk of chronic disease, adults should engage in at least 30 minutes of moderate-intensity exercise at least five times a week.

As you can see, the biggest reduction in mortality, about a 30 percent drop, is between sedentary individuals and those who exercise sixty minutes a week.

(Moderate-intensity aerobic activity is defined as between 50 and 70 percent of your maximum heart rate; vigorous-intensity aerobic activity is 70 to 85 percent of your maximum heart rate.)

Finally, they recommended everyone also do some weights twice a week.

but the benefits eventually level off.

the largest benefit came from just ninety weekly minutes of exercise, yielding an average 20 percent reduction in the risk

attain another 20 percent reduction in risk beyond the benefits of ninety weekly minutes, we’d have to exercise another five and a half hours for a total of seven hours per week.

But there is no optimal, most beneficial dose of exercise.

they found that joggers who ran slowly over moderate distances had 30 percent lower death rates than sedentary individuals,

the serious runners who ran the most and the fastest died at the same rate as the non-exercisers.

we are probably adapted for moderate rather than extreme exercise.

“these findings reinforce the notion that light to moderate doses of exercise have a substantial positive impact on health

One long-standing and very legitimate concern is the potential effect of too much exercise on the immune system.

Dr. William Cowles suggested that fatigue from “violent exercise” contributed to higher rates of pneumonia based on his experiences treating the staff and students at the Groton School just outside Boston.

Additional studies found lower levels of disease-fighting white blood cells in the bloodstream and saliva immediately following intense bouts of vigorous exercise.

“open window”

but just how much exercise is too much needs further study.

there is evidence that regular, moderate physical activity can help protect against some contagious diseases,

the extent to which high doses of exercise suppress the immune system’s ability to ward off infections and under what conditions.

low levels of moderate exercise (twenty to thirty minutes of daily running) doubled their rate of survival compared to sedentary mice, but extremely high levels of exercise (two and a half hours of running a day) caused them to die at even higher rates.

an increased likelihood of developing atrial fibrillation,

Aerobic exercise is sustained physical activity fueled by burning oxygen.

Typical aerobic exercises include fast walking, jogging, cycling, or (ever since Jack LaLanne and Jane Fonda) working out at home in front of the TV.

the most obvious benefits are cardiovascular, hence the term “cardio.”

Within muscles, it increases the number of mitochondria, promotes the growth of muscle fibers, and increases their ability to store carbohydrates and burn fat.

terms of metabolism, it burns harmful organ fat, improves the body’s ability to use sugar, lowers levels of inflammation, and beneficially adjusts the levels of many hormones including estrogen, testosterone, cortisol, and growth hormone.

In moderation, aerobic exercise stimulates the immune system,

aerobic exercise increases blood flow to the brain and elevates the production of molecules that stimulate brain cell growth, maintenance, and function.

Short bursts of intense cardio elevate heart rate and oxygen consumption close to their upper limit, usually above 85 or 90 percent of maximum rate.

anywhere from ten to sixty seconds,

regardless of age, fitness, obesity, and health.

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

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.

Most of all, it doesn’t deliver all the diverse benefits of regular aerobic activity.

Resistance exercise can also help prevent bone loss, augment muscles’ ability to use sugar,

enhance some metabolic functions, and improve cholesterol levels.

supplement cardio with weights, especia...

involving all major muscle groups (legs, hips, back, core, sh...

weights, moderate-intensity aerobic exercise, and

HIIT have different, complementary effects on the body.

exercise several hours a week, mostly cardio but also some weights, and keep it up as you age.