Welcome to our 5-part series delving into the fascinating research being performed in the emerging field of sedentary physiology. In Part 1 we discussed the basics of sedentary physiology, and in Part 2 we discussed the relationship between total sedentary time and negative health outcomes. Today we look at the impact of breaks in sedentary time on health.
Yesterday we reviewed the evidence which links total sedentary time with increased risk of both morbidity and mortality. But what about the manner in which you accumulate that sedentary time? For example, does 7 hours of continuous sitting have the same impact as 7 hours of sitting interspersed throughout the day? According to the evidence available so far – probably not.
A recent study by Genevieve Healy examined this issue in participants of the large Australian Diabetes, Obesity and Lifestyle (AusDiab) Study. A total of 168 men and women aged 30-87 years were required to wear an accelerometer (an objective measure of bodily movement) during all waking hours for 7 consecutive days. Total sedentary time was measured as the number of minutes/day during which the accelerometer had a count of less than 100/min – a level of activity associated with reading or typing. A break in sedentary behavior was defined as any interruption of at least one minute during which the accelerometer count rose above 100 counts/min. This level of activity is typical of standing from a sitting position or walking a short distance (i.e. walking to the bathroom).
And what did the study find?
The greater the number of breaks taken from sedentary behavior, the lower the waist circumference, body mass index, as well as blood lipids and glucose tolerance. This was true even if the total amount of sedentary time and physical activity time were equal between individuals – the one who took breaks more frequently during their time at the office or while watching television was less obese and had better metabolic health. Importantly, the breaks taken by the individuals in this study were of a brief duration (<5 min) and a low intensity (such as walking to the washroom, or simply standing).
Unfortunately few other studies have been published in this area, but several interventions are currently underway in the USA and Australia, and I am very eager to see their results and post them here on the blog. In the meantime, what are the practical implications of this epidemiological study?
While we should all be aiming to limit the time spent in sedentary behavior and increasing our time spent performing moderate-intensity physical activity, for many of us working in front of computers, countless hours of sedentary time are inevitable. However, according to this study, simply taking frequent short breaks from being lazy may have significant implications on our health. For example, while writing this post (total time of approximately 1 hour) I have counted myself getting up from the computer 3 times – some of these ‘breaks’ were a mere 30 second walk to the kitchen to get a drink. Thus, getting out of your chair at work once every hour to walk to the washroom, or to fill up your bottle of water, or to chat with a co-worker may be a good way to get your ‘breaks’ in. Similarly, while watching TV, why not get up and move around during the commercial break – by doing so you will give your body a break from doing nothing, which could have real health benefits.
As we’ve discussed so far this week, the available evidence suggests that both the total amount of sedentary time and the manner in which it accumulates are related to negative health outcomes, regardless of how physically active we are. But what physiological mechanisms are at play, especially given that these relationships appear to be independent of physical activity? For the answer(s), be sure to check back for Part 4 in our series tomorrow (now online here).
Travis & Peter
Healy, G., Dunstan, D., Salmon, J., Cerin, E., Shaw, J., Zimmet, P., & Owen, N. (2008). Breaks in Sedentary Time: Beneficial associations with metabolic risk Diabetes Care, 31 (4), 661-666 DOI: 10.2337/dc07-2046