Flashback Friday: 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.