Commentaries on Physical Activity and Health
The Physical Activity Guidelines for Americans, 2nd edition
Reflections from Advisory Committee Member David Buchner
What has been your role in the federal physical activity guidelines?
I have had two roles. When I was Chief of the Physical Activity and Health Branch at CDC, I was privileged to chair the writing committee for the 2008 Physical Activity Guidelines for Americans. For the 2018 updated of the Guidelines, I was member of the Physical Activity Guidelines Advisory Committee which drafted the scientific report on which the 2018 Guidelines are based.
Why is it important that the Guidelines are regularly updated?
It is important, even if we do not expect major changes in guidelines. Indeed, a measure of success for guidelines is that major changes are unusual, reflecting the fact that the science on which the guidelines are based is strong and well established. At the same time, the evidence on benefits of physical activity has grown steadily over the decades. We need regular updates to guidelines, so as to review and integrate this new evidence. For example, I see the current evidence on sedentary behavior as sufficient only for qualitative guidance (e.g. “sit less”), but I expect research will eventually allow guidelines to contain quantitative guidance (e.g. “limit sitting to no more than 350 minutes/day”).
How would you describe the connection between the Guidelines and NPAP?
There is a strong connection. The guidelines affirm there is strong evidence of the health benefits of physical activity and lay the basis for federal policy regarding physical activity. Yet the physical activity and public health community is well aware that simply publishing guidelines is insufficient–one needs to take action. The idea for the first NPAP was that a comprehensive plan for increasing levels of physical activity in Americans would be released within a year or two of the 2008 Guidelines (and NPAP was). The 2016 update of NPAP explicitly states “…the Plan focuses on strategies for increasing the types and amounts of physical activity recommended by current public health guidelines.” [p.2]
Was there anything in the 2018 Guidelines or PAGAC report that surprised you?
I continue to be amazed and impressed by the breadth and size of the health benefits of physical activity. Fall prevention exercise programs can lower risk of fall-related injuries by 40% or more?! Risk of at least 8 cancers is reduced by regular PA?! Regular physical activity can lower risk of Alzheimer’s disease by 40% or more?! If I chose to do higher amounts of activity, I can lower my risk of major functional limitations and disability by 50% or more?! Some dose-response analyses show higher amounts of physical activity can reduce risk of premature mortality by 40% in people my age?!
Was there anything in the PAGAC report that disappointed you?
The guidelines recommend an hour/day of physical activity for youth with vigorous activity occurring on at least 3 days a week. At the same time, adults need only do 30 minutes/day on five days a week of moderate-intensity activity to meet the main aerobic guideline—no vigorous activity required. It doesn’t make sense to me that, on a person’s 18th birthday, the recommendation would change so much and so abruptly. I was disappointed that existing research was insufficient to provide more guidance on appropriate levels of physical activity in young adults as they transition from youth to middle age.
How do you predict future versions of the guidelines will change?
I favor research and guidelines based upon the 24 hour activity cycle model 1. Such guidelines would provide quantitative guidance on healthy amounts of sleep, sitting time, light activity and moderate-to-vigorous activity (MVPA). However, I feel much more research is needed before this approach can be operationalized.
What research would you suggest as important for future guidelines?
The PAGAC report makes numerous research recommendations. However, based upon recent research in aging and physical activity, I would emphasize that we need more research on measures of volume of physical activity in older adults. Because of differences in how measures of volume change with age, I believe research studies should include more than one measure. To illustrate this point, suppose an older adult has the same oxygen uptake each week over 20 years between age 65 and 85—essentially the same MET-minutes per week of activity. By this measure of volume, the person’s physical activity level is stable. What will happen to their accelerometer counts? They will go DOWN with age, because energy cost of activity is going up, so less movement is required to achieve the same MET-minutes of activity. What will happen to volume of activity as assessed by relative intensity and heart rate? It will go UP with age. Due to age-related decline in maximum heart rate, the moderate-intensity walking at a heart rate of 110 at age 65 has become relatively vigorous by age 85. Indeed, cross-sectional studies from the Baltimore Longitudinal Study on Aging show that total accelerometer counts go down with age while minutes of MVPA (assessed by heart rate monitors) go UP with age 2, 3. If more studies were to include multiple measures of volume, we could develop a better understanding of how volume and intensity influence health outcomes in older adults.
Any final comments?
I thought the launch of the 2018 Guidelines was highly successful. I would point out that CDC has carefully considered their leadership role in promoting physical activity, and in advance of the launch, proposed an approach called “Active People, Healthy NationSM” emphasizing 5 action steps: program delivery, partnership mobilization, effective communication, cross-sectoral training, and continuous monitoring and evaluation 4.
1 Rosenberger ME, Fulton JE, Buman MP, et al. The 24-Hour Activity Cycle. Medicine & Science in Sports & Exercise. 2019;51(3):454-464. doi:10.1249/mss.0000000000001811.
2 Schrack JA, Zipunnikov V, Goldsmith J, et al. Assessing the “Physical Cliff”: Detailed Quantification of Age-Related Differences in Daily Patterns of Physical Activity. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences. 2013;69(8):973-979. doi:10.1093/gerona/glt199.
3 Schrack JA, Leroux A, Fleg JL, et al. Using Heart Rate and Accelerometry to Define Quantity and Intensity of Physical Activity in Older Adults. The Journals of Gerontology: Series A. 2018;73(5):668-675. doi:10.1093/gerona/gly029.
4 Fulton JE, Buchner DM, Carlson SA, et al. CDC’s Active People, Healthy NationSM: Creating an Active America, Together. Journal of Physical Activity and Health. 2018;15(7):469-473. doi:10.1123/jpah.2018-0249.