Sedentary Physiology Part 5 – Future Directions

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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!

Travis

ResearchBlogging.orgTremblay, MS, Colley, RC, Saunders, TJ, Healy, G, & Owen, N (2010). Physiological and health implications of a sedentary lifestyle Applied Physiology, Nutrition and Metabolism

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21 Responses to Sedentary Physiology Part 5 – Future Directions

  1. Jennifer says:

    What a great series! Thank you for taking the time to make this type of science accessible to laypeople.

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  2. Pingback: Sedentary Physiology Part 4 – How Does Sitting Increase Health Risk? | Obesity Panacea

  3. Carol says:

    I second what Jennifer said. Great series and easy for me to understand and apply in my regular life.

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  4. Travis Saunders, MSc, CEP says:

    Thanks ladies! It’s always great to hear when people find our content useful! :)

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    • Anne Higgins says:

      I also thank you. I am a Community Mental Health Nurse and work with seriously mentally ill people. As you know this population has an average life span of 20-25 years less than the general population. The rates of obesity and physical inactivity are very high (for a number of reasons) and any information I can get about helping people with these issues is always welcome. I look forward to hearing more about the research in the future.

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  6. Rhodia says:

    Great series! Thanks for doing this.

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  7. Phil Woodcock says:

    Hi there,

    Hope you are still reading comments on this series. I’m wondering if any of the future studies around this area might involve long term wheelchair users. Interested as a manual wheelchair user myself. It would be really interesting to know what level of activity might be required to offset my permanent sitting (daytime) or lying down (sleeping).

    I’m just a lay person – not a science background

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  8. Pingback: Even if you exercise, it may not matter if you sit too much. Should Northfield’s schools be using stand-up desks? « Locally Grown Northfield

  9. innok says:

    While i was reading i could not but think about going to movie theater’s. We all do it and some films are up to 3 hours long! I sure wish they had intermissions like in the olde tymes.

    Great article! thank you

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  10. LeonRover says:

    Hi Travis
    A great set of 5 blogs.

    I really like the concept of trying to capture th INTERMITTENCY of Light Activity. I particularly focused on the representation of the 12 hour data and the descriptions of prolonger etc.

    A couple points occur:

    Have similar studies been done using Heart Beat Monitors?

    How does the cut-off of 100 step/min relate to heart beat rate?

    Great, great new idea.

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    • Travis says:

      Hi Leon,

      As far as I know there’s nothing looking at sedentary behaviour and heart rate, but I don’t know that heart rate would really be able to pick it up. Simply going from sitting to standing *may* be enough to prevent the metabolic impact of excess sitting – and that type of shift may be too subtle to be detected by heart rate.

      I’m not sure I understand the 100 steps/minute question. Are you referring to post # 3, when we talk about 100 counts being considered a “break” in sedentary time? That is how sedentary behaviour is defined using accelerometers, but it doesn’t have much real-world implications, unless you are analyzing accelerometer data.

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      • LeonRover says:

        Hi Travis

        The data as presented seem to suggest that different steps/min relate to an oxidation burn in METs – if so, what is that?

        For most people VO2 rises linearly with heart rate – with an average resting rate of 70-75 bpm – I assume corresponds to 1 MET. I conjecture that a heart monitor could act as a proxy for an accelerometer.

        Any thoughts?

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  11. Renee says:

    So at this point, given current research, how often should those of us who work at a desk all day long be taking breaks? And how long should each break be? There may not be a clear answer, but what would be your best guess?

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  13. Jim says:

    LIFE EXPECTANCY OF BARBERS. I don’t know if a study has been done, but compared to the complexity of many studies, it MIGHT be a relatively simple task to find birth and death information for a few thousand men who were barbers and compare their life expectancy to that of the general male population, or even better, to another group or groups such as accountants or lawyers. The results would be interesting.

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  14. Williams says:

    Great research to share in this forum. I’ve shared with my colleagues in public health. We need more research in this area especially from an advocacy perspective. Thanks!

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    • Travis Saunders, MSc, CEP says:

      Thanks William, glad to hear it’s been useful to you!

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  15. Pingback: Sedentary Lifestyle: What counts as sedentary? - Quora

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  17. Kara Faithfull says:

    Hi Travis,

    I am a Master of Health Science candidate at AUT University in New Zealand.
    As part of my degree we have been analyzing the effect of postprandial lipemia on LPL uptake in children (8-12 y). I would be very interested to discuss further your research and our findings. I can not seem to find your email address on the site, but you are welcome to contact me at kara.faithfull@aut.ac.nz
    I look forward to your response.

    Kara

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