My personal highlight from day 2 of the Global Summit on the Physical Activity of Children was a debate on the relative importance of sedentary behaviour and physical activity for child health. Arguing for physical activity was Dr Ulf Ekelund, while sedentary behaviour was argued by David Dunstan. Rather than go point by point, I thought I’d touch on some of the main themes that were discussed. And just to be clear, this was my perception of the debate, so if anyone had a different perception I’d love to hear it in the comments (similarly, if anyone feels I misunderstood the points of the speakers please let me know).
Objective and Subjective Sedentary Behaviour Are Not the Same
One of the first points raised by Ulf Ekelund is that objectively measured sedentary behaviour is not consistently associated with health outcomes in children. In contrast, screen-based measures of sedentary behaviour are much more consistently linked with negative health outcomes. Take, for example, this paper from my PhD that found that screen time was strongly associated with health risk in kids aged 8-11 years, whereas objectively measured sedentary time showed no association with health outcomes. In other words it may be the screens that matter, rather than the sitting.
Physical Activity Gives the Biggest Bang For Your Buck
In contrast to the wishy washy evidence linking objectively measured sedentary behaviour and health in kids, there is pretty consistent linking physical activity with health in this same group. Dr Ekelund has done some interesting work in this area. For example, the below figure shows data from one of Dr Ekelund’s studies which found that moderate intensity physical activity was associated with health outcomes in kids irrespective of how much time they spent being sedentary. In contrast, sedentary behaviour was not associated with any health outcome after adjusting for moderate physical activity. In other words, physical activity was the more important to health than sedentary behaviour for these kids (JP Chaput found similar results using a cohort of Canadian children).
Kids and Adults Are Not the Same
This area was touched on by both researchers, and is a topic I dealt with a lot during my thesis work. For example, both Dr Dunstan (here) and others (here) have shown that even acute exposure to uninterrupted sitting results in rapid increases in health risk in adults. In contrast, my own work and the work of Dr Susan Sisson have failed to find any acute impact of sitting in kids or teens.
Similarly, the evidence linking sedentary behaviour with chronic health conditions is also much stronger in adults than in children. Dr Ekelund pointed out (and I agree) that kids are inherently very healthy, which can make it tough to find health-related associations in this age group (e.g. even if a behaviour is bad for kids’ health, it has to be really bad for health in order to pick up a relationship using current methodologies).
On this note, I was surprised that Dr Dunstan did not point out that sedentary behaviour tracks into adulthood. So while Dr Ekelund is absolutely right that the data isn’t as strong in kids as in adults, we know that the most sedentary kids become the most sedentary adults (and we know that sitting is very bad in adults). So even if you believe that sitting has no health impact whatsoever during childhood, it’s still probably a bad habit to get into.
Should We Reduce Bad Behaviour, or Increase Good Behaviour?
Both Dr Dunstan and Dr Ekelund made it clear that the real goal should be to sit less AND exercise more. However, I think there was some real disagreement on which approach to take. Dr Ekelund argued that physical activity is too important to not be a primary focus. In contrast, Dr Dunstan argued that 50 years of focusing on physical activity has done little to actually increase physical activity levels. He argued that instead we should try focusing on reducing sedentary behaviour, which might lend itself more easily to intervention (e.g. it may simply be easier to get people to sit less than to exercise more). Finally, I think Dr Ekelund had an excellent point when he pointed out that Running > Jogging > Walking > Standing > Sitting when it comes to health.
That was my view of the debate! A lot of the topics covered were similar to those that I discussed in the literature review to my PhD thesis (recently published in the Canadian Journal of Diabetes), which you can download here for a more thorough discussion.
I’ll be live-blogging throughout the day again tomorrow, as will a great many others. To follow the conference live on Twitter just search for the #AHKCSummit hashtag.