How Much Should You Exercise?

“How Much Should You Exercise?”
Researchers who accept grants from the Coca-Cola Company may call physical inactivity “the biggest public health problem of the 21st century.” But actually, physical inactivity ranks down at number five in terms of risk factors for death in the United States and number six in terms of risk factors for disability. And, inactivity barely makes the top ten globally. As we’ve learned, diet is by far our greatest killer, followed by smoking. Of course, that doesn’t mean you can just sit on the couch all day.

Exercise can help with mental health, cognitive health, sleep quality, cancer prevention, immune function, high blood pressure, and lifespan extension. If the U.S. population collectively exercised enough to shave just 1 percent off the national body mass index, 2 million cases of diabetes, one and a half million cases of heart disease and stroke, and 100,000 cases of cancer might be prevented. Ideally, how much should we exercise? The latest official physical activity guidelines recommend adults get at least 150 minutes a week of moderate aerobic exercise, which comes out to be a little more than 20 minutes a day.
That’s actually down from previous recommendations from the Surgeon General, and the CDC, and the American College of Sports Medicine, which recommended at least 30 minutes each day. The exercise authorities seem to have fallen into the same trap as the nutrition authorities, recommending what they think may be achievable, rather than simply informing us what the science says and letting us make up our own mind.

They already emphasize that any physical activity is better than none; so, why not stop patronizing the public and just tell everyone the truth? It is true that walking 150 minutes a week is better than walking 60 minutes a week. Following the current recommendations for 150 minutes appears to reduce your overall mortality rate by 7 percent compared to being sedentary. Walking for only 60 minutes a week only drops your mortality rate about 3 percent. But, walking 300 minutes a week drops overall mortality by 14 percent. So, walking twice as long— 40 minutes a day, compared to the recommended 20— yields twice the benefit. And, an hour-long walk each day may reduce mortality by 24 percent! (I use walking as an example, because it’s an exercise nearly everyone can do, but the same goes for other moderate-intensity activities, such as gardening or cycling.) This meta-analysis of physical activity dose and longevity found that the equivalent of about an hour a day of brisk, 4 miles per hour walking was good, but 90 minutes was even better. What about more than 90 minutes? Unfortunately, so few people exercise that much every day that there weren’t enough studies to compile a higher category.

If we know 90 minutes of exercise a day is better than 60 minutes, is better than 30 minutes, why is the recommendation only 20 minutes? I understand that only about half of Americans even make the recommended 20 minutes a day; so, the authorities are just hoping to nudge people in the right direction. It’s like the dietary guidelines advising us to “eat less candy.” If only they’d just give it to us straight.