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, in Part 2 and Part 3 we looked at the association of sedentary time with both death and disease, and in Part 4 we looked at the mechanisms underlying these relationships. Today we will look at where future work in the field of sedentary physiology is heading.
Given the research that we have reviewed this week, I personally find the evidence pretty convincing that too much sedentary behaviour is bad for your health. But as several readers have pointed out, what qualifies as “too much” sedentary behaviour? And as others have asked, what can be done to reduce or prevent the negative impact of excess sedentary behaviour? Is simply standing every few minutes enough, or do we need to be exercising at a relatively high intensity? Or is the only option to simply cut down dramatically on the amount of sitting that most of us perform on a daily basis? Unfortunately, no one knows the answers to any of these questions, but as I have mentioned earlier, several lab-based studies are going on in Australia and the USA which will hopefully be published in the next year and shed light on these issues.
However, regardless of the findings of the studies that are currently ongoing, there is a need for many more studies in this emerging field. With this in mind, I thought it would be worth pointing out a number of important issues and possible directions for future research, should anyone feel inclined to take the advice of a lowly grad student working in this area. Here are some of the issues that I feel are important to consider, in no particular order (as always, I’d love to hear other suggestions in the comments!):
1. Think twice before you define an individual as “sedentary”.
Are they really “sedentary” (e.g. they sit too much) or are they just insufficiently physically active? When most exercise physiology papers refer to an individual as being “sedentary”, it simply means that they are not meeting physical activity guidelines. But as we discussed Monday, sitting too much (e.g. being sedentary) is not the same as being insufficiently physically active, and it is important that we differentiate between these two distinct behaviours. This may seem like a trivial issue, but from personal experience I can tell you that it is incredibly difficult to stay up-to-date on research in the field of “sedentary physiology” when everyone defines “sedentary” in a different way. I think that the definition that we outlined in this recent paper makes a lot of intuitive sense, but we really need to ensure that everyone starts using a common terminology, whatever that may be.
2. Don’t just ask about sedentary behaviour – measure it directly.
As you may have noticed this week, a lot of the research on sedentary behaviour has used self-report data. For example, the most common “assessment” of sedentary behaviour simply involves asking people how much TV they watch. Since TV watching typically involves sitting, this is thought to be a reasonable proxy for sedentary behaviour. And while this is better than nothing, a recent paper using a nationally representative sample of more than 5700 Americans suggests that self-reported TV watching is only weakly associated with directly measured sedentary time using accelerometers. This is not a huge surprise since self-reported data is generally less accurate than direct measurement, especially for socially desirable behaviours like TV watching. And even if people could accurately recall how much time they spend watching TV every day, this is still only one of several common sedentary behaviours. So while I would strongly suggest that people use direct measures of sedentary behaviour (such as accelerometers) whenever possible, it is also important that we develop questionnaires that are valid and reliable at assessing sedentary behaviours other than simply TV watching (driving, computer time, etc).
3. We need more lab-based studies
As readers have also pointed out in the comments earlier this week, several of the studies that I have discussed in this series have been cross-sectional epidemiological studies. These studies are interesting, but they can’t really explain whether excess sedentary behaviour causes health problems, or whether health problems cause people to engage in more sedentary behaviour. There have been a few notable longitudinal studies examining the relationship between sedentary behaviour and mortality (as discussed in Part 2 of this series), as well as a number of interesting lab-based studies in animals and humans (as discussed in Part 4). And yet there seems to be an almost unending flood of papers reporting cross-sectional relationships between body weight and TV watching, despite the relationship already being well characterized by numerous studies and reviews (seriously – we know there’s a relationship between TV watching and BMI… it’s time to move on to bigger and better things!).
If we are to advance our understanding of sedentary physiology, it is time that we focus our efforts on understanding the mechanisms underlying these relationships, which will require lab-based interventions that examine the physiological impact of controlled doses of sedentary behaviour. In other words, it is time that we apply the exercise physiology paradigm of lab-based interventions to this new field of sedentary physiology. Along with longitudinal observational studies, and randomized trials which aim to reduce sedentary behaviour among free-living individuals, these studies will dramatically improve our understanding of the relationship between sedentary behaviour and chronic disease.
4. We need a better understanding of the determinants of sedentary behaviour
While it is now reasonably clear that sitting “too much” is bad for your health, we don’t really know what factors influence the amount of time that you spend sitting. And until we understand the determinants of sedentary behaviour, it is obviously difficult to implement public health interventions that will help reduce sedentary time. Just as ecological models have been used to help us improve our understanding of the determinants of physical activity, we now need to develop similar models that can be applied to sedentary behaviour. And once we know the determinants, we can attempt to modify them and assess whether there is a noticeable impact on sedentary behaviour and/or health outcomes.
And that brings us to the end of this series of sedentary physiology! As I mentioned earlier in the week, several colleagues and I recently published a review paper on the field of sedentary physiology, which is what led me to write this series in the first place. The publication of this paper has been a pretty exciting moment for me since it was my first peer-reviewed publication with my current lab group here in Ottawa, and also because the paper was a collaboration with two members of the AusDiab study team in Australia who have published some of the most influential papers in the field of sedentary physiology (including the “breaks in sedentary time” paper that we focused on in Part 3 of this series earlier in the week). This series on sedentary physiology can be thought of as the Cliffs Notes version of the paper, and I’d encourage anyone looking for a more detailed discussion of sedentary physiology to check out the pdf here (the website of the journal itself, which provides open access to everyone with a Canadian IP address, is here). Let me know if anyone has trouble accessing it in either location (I’m happy to send you a copy). Thanks to everyone who joined the discussion this week, it has been a real pleasure spending a whole week writing solely about my favourite area of research!