Americans Fail to Heed Physical Activity Guidance, Sitting More

Patrice Wendling

August 01, 2019

Americans did not lean in; they sat down. A new NHANES analysis concludes that adherence to aerobic activity recommendations remained flat after the release of the first Physical Activity Guidelines (PAG) for Americans, while sedentary time increased by nearly an hour a day.

The 2008 guidance recommends that adults participate in at least 150 minutes a week of moderate-intensity or 75 minutes of high-intensity aerobic activity and 2 or more days a week of muscle-strengthening activities of at least moderate intensity.

After examining data from 27,343 participants in the National Health and Nutrition Examination Surveys from 2007 to 2016, researchers found that adherence to the aerobic activity recommendations was 63.2% in 2007/08 and 65.2% in 2015/16, a nonsignificant difference (P = .15 for trend).

The time spent on sedentary behavior, however, increased significantly from a weighted mean of 5.7 hours per day to 6.4 hours per day over the same period (P < .001 for trend). The increase was consistent across subgroups, but highest among people with a college education or above (peak, 8.2 hours in 2013/14) and those with obesity (peak, 8.0 hours in 2013/14).

"Of course this study itself cannot tell us why, but I think the major reason for these results is the society is becoming more and more sedentary," senior author Wei Bao, MD, PhD, University of Iowa, Iowa City, told | Medscape Cardiology. "The life we are having is more convenient than we used to be. It means there are fewer and fewer opportunities for us to do any labor."

He noted that people used to spend significant amounts of time shopping for groceries and other items or cleaning their homes, but now turn to online shopping, in-home deliveries, and robotic cleaners. "This kind of automation is a wonderful intervention. We save a lot of time and for some people the saved time may be spent exercising," Bao said. "But for a lot of other people, they will spend that time in the couch or spend it sitting down for TV or just to look at our smartphones."

Another possible explanation is that evidence and public awareness about the harms of sedentary behavior was just emerging when the first PAG was published, observed Bao. Recommendations on sedentary behavior subsequently found their way into Australian physical activity guidelines in 2014 and the Canadian 24-hour movement guidelines for children and youth in 2016.

The updated PAG, released late last year, retains the 2008 physical activity recommendations but also calls on adults to "move more and sit less throughout the day."

Preventive cardiologist Gina Lundberg, MD, clinical director of Emory's Women's Heart Center in Atlanta, said the study had a nice 50-50 mix of men and women, but also noted that for much of the study period, more than 60% of participants were college educated or above, suggesting white-collar jobs spent in front of a computer.

"Many people in that group aren't just working 40 hours a week and then having time to exercise, shop healthy, and get a good night's sleep," she said. "In fact, that's a big thing I hear from my patients. My practice is on the north side of Atlanta, and most of my patients have not just college degrees but advanced degrees, and the thing I hear constantly from them is, 'I'm at work by 7 AM, I don't get home till 7 or 8 PM. When do you want me to exercise, Dr Lundberg?' "

Both Lundberg and Bao suggest that although technology may be tipping the scale toward more sedentary time, it may also keep Americans exercising at work through new products like under-desk bikes and ellipticals, treadmill and standing desks, and stability ball chairs. Fitbits, Smartwatches, and phone apps are also useful to track time spent exercising, sitting, or on social media.

"When you get a report that tells you you spent 8 hours on your phone this week, that's when I tell myself you've gotta cut back, Gina," Lundberg said from experience. "I will say that I use my phone text for work to contact other doctors, to set up consultations with other patients, so it's not all just doing social media, but it's still a lot of time on the phone. So I think the app that notifies you of your weekly phone usage is actually a good reminder to keep you out of trouble."

The finding that Americans spent an extra hour a day of sedentary behavior is in line with previous work, but what's unique about this study is that it measured not only leisure-time physical activity but also work-related and transportation-related physical activity, Katrina L. Piercy, PhD, RD, US Department of Health and Human Services, Rockville, Maryland, emphasizes in a related editorial.

This led to an adherence rate of 65.2% for aerobic exercise, which is higher than estimates of 54.1% from the 2017 National Health Interview Survey (NHIS) and 44.6% from 2015/16 NHANES leisure-time physical activity data.

The study, however, focused exclusively on aerobic activity and did not include the muscle-strengthening component, she noted. This is important because overall adherence to PAG tends to be "markedly lower" because of lower rates of muscle-strengthening activity. For example, 2017 NHIS data show 54.1% of adults met the aerobic component, 27.7% the muscle-strengthening component, and only 24.7% both components.

Although adherence targets are important, Piercy points out that the updated PAG removes the "10-minute bout" requirement, which states that exercise needs to be at least 10 minutes. "Ideally, people should meet the PAG targets to obtain the most of the health benefits, but considering that currently 25% of adults do no leisure-time physical activity, any increase in physical activity is good," she said.

Further nationwide efforts appear to be warranted to not only promote physical activity but also reduce sedentary time in the United States, the authors conclude in the study, published in the July issue of JAMA Network Open.

"It would be great if there were campaigns from the leading medical organizations," Bao said. "I think the scientific evidence has emerged to support this kind of campaign, so now is the right time for action."

National campaigns, such as those currently featuring former smokers, can be powerful, but "the message needs to be crafted in a sensitive way," cautioned Lundberg. "A positive message is hard to do because two out of three people in America are overweight or obese. We want people to get healthy. We don't want to body shame."

The authors, Lundberg, and Piercy report having no relevant conflicts of interest.

JAMA Netw Open. 2019 Jul 3;2(7):e197597 and e197575. Full text, Editorial

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