This commentary presents Dr. Katzmarzyk’s views on the topic of a research article which he published in the May 2014 issue of Medicine and Science in Sports and Exercise® (MSSE).

Over 60 years of epidemiological, clinical and basic science research support the 2008 Physical Activity Guidelines for Americans, which call for 150 minutes of weekly moderate-to-vigorous physical activity for adults. More recently, scientists have developed an interest in understanding the health effects associated with the low end of the human movement spectrum — namely sedentary behavior. A dozen or more cohort studies from several countries document a positive association between sitting and the risk of premature mortality, even after statistically controlling for levels of leisure-time moderate-to-vigorous physical activity. The results generally support the notion that sedentary behavior and “physical activity” should be considered as distinct, potentially independent behaviors. One could easily imagine a situation where someone is meeting the physical activity guidelines but spending a large fraction of the day sitting.

If physical activity is good and sitting is bad, what about standing? The results of my study, recently reported in MSSE, indicate a significant negative association between time spent standing and the risk of mortality in a large sample of Canadian adults. People who reported standing “almost all of the time” had a 33% lower risk of all-cause mortality over 12 years compared to people who reported standing “almost none of the time”, even after controlling for a number of covariates including leisure-time physical activity. There was a dose-response relationship, such that successively lower mortality rates were observed at successively higher levels of daily standing. The relationship between standing and mortality was significant only among adults who were not meeting the physical activity guidelines. Taken together, the results suggest that standing is a healthy, low-energy expenditure activity among physically inactive adults.

A reasonable question to ask is whether sitting and standing are simply the inverse of one another. In my study, the correlation between sitting and standing was -0.52, indicating that although these behaviors are associated with each other, standing is not simply the inverse of sitting. One might substitute sitting with a range of other movements, such as activities of daily living and leisure-time physical activity. Several studies have begun to find positive associations between “light” activity (< 3 METS) and health, which further extends the paradigm of human movement and health. Thus, the finding of a negative association between standing and mortality adds another piece to the puzzle. Given the established association between sitting and mortality, it seems that beneficial associations with health can be detected even with very low-level energy expenditure activities, such as standing.

Improvements in physical activity monitoring technology (e.g. accelerometers) now allow for the quantification of human movement across the entire movement spectrum from sleep to very vigorous exercise. I predict that the use of this technology will reveal further associations with health across the spectrum of human movement. The challenge that we will face as exercise and sport scientists is in the communication of this research to the public in a way that conveys the importance of avoiding extended periods of sedentary behavior while at the same time not downplaying the importance of moderate-to-vigorous physical activity as a preventive health behavior.