Released in 2018, the Second Edition of the Physical Activity Guidelines for Americans highlights the importance of physical activity for improving a number of health outcomes. These recommendations were largely based upon decades of observational and experimental studies documenting the health effects associated with moderate and vigorous intensity physical activity. However, a new twist in the recommendations and the accompanying 2018 Physical Activity Guidelines Advisory Committee Scientific Report is the consideration of sedentary behavior (i.e. sitting) as having a potential role to play in the association between physical activity and health.

A recent ACSM Pronouncement published in Medicine and Science in Sports and Exercise summarized the evidence for an association between excessive levels of sedentary behavior and negative health outcomes such as type 2 diabetes, cardiovascular disease, and premature mortality. While the evidence is still accumulating, it appears as though the effects of sedentary behavior on health may not be completely independent of physical activity (and vice versa). Therefore, in formulating the questions to be examined by the 2018 Physical Activity Guidelines Advisory Committee, there was considerable interest in understanding whether the amount of time spent sitting modifies the association between physical activity and health. One potential impact of such an interaction could be the refinement of physical activity recommendations based on the amount of sedentary time that a person experiences, for example based on their occupational requirements.

In order to address this question, the Committee turned to a large pooled meta-analysis of over one million people studying the joint associations between physical activity, sedentary behavior and mortality. The results indicated that those who were the most sedentary experienced the greatest relative reductions in mortality risk associated with increases in moderate-to-vigorous physical activity. Furthermore, individuals who were the most sedentary required even higher amounts of physical activity to achieve the same level of absolute mortality risk as people who are less sedentary.  

It is clear that moderate-to-vigorous physical activity should be part of everyone’s daily routine, especially for those who sit for large portions of the day. The new guidelines emphasize that for substantial health benefits, adults should accumulate at least 150 minutes to 300 minutes a week of moderate-intensity, or 75 minutes to 150 minutes a week of vigorous-intensity aerobic physical activity (or an equivalent combination of moderate and vigorous activity). These recommendations highlight that substantial health benefits accrue within a range of activity. In my opinion, people who spend a large part of their day sitting should aim for the higher end of the range (i.e. 300 minutes per week) in order to help negate the effects of excessive levels of sedentary behavior.

Learn more about the Physical Activity Guidelines for Americans 2nd Edition

Peter Katzmarzyk, PhD, FACSM is Professor and Associate Executive Director for Population and Public Health Sciences at the Pennington Biomedical Research Center in Baton Rouge, LA. He recently served on the 2018 U.S. Physical Activity Guidelines Advisory Committee for the U.S. Department of Health and Human Services.