This afternoon at CSEP 2011 I attended a session titled “Childhood obesity prevention: new insights into (in)activity behaviours”. All of the presenters come from the Healthy Active Living and Obesity Research Group at the Children’s Hospital of Eastern Ontario Research Institute (Full Disclosure: I work with all of the presenters on a regular basis).
Physical Activity in Canadian Children and Youth
The first speaker was Dr Rachel Colley, who discussed the relationships between physical activity and health in children and youth, focusing on her work using the Canadian Health Measures Survey (CHMS) (discussed previously on Obesity Panacea here). For those who are unfamiliar with the CHMS, it is a nationally representative survey of the health of Canadians, using direct measures of health, body composition, fitness, and physical activity. For those familiar with the NHANES survey in the US, the CHMS is its Canadian counterpart.
As we have discussed previously here on Obesity Panacea, data collected during the initial cycle of the CHMS suggests that Canadian kids spend the vast majority of their waking hours (~8 hours/day) engaging in sedentary behaviour, while they spend just less than an hour per day engaging in moderate-to-vigorous physical activity (although only 7% achieve the Canadian PA guidelines of 60 minutes on at least 6 days/week). On the bright side, however, the majority of kids are getting at least 30 minutes of PA on at least 3 days/week. Finally, they also found significant inverse relationships between PA and weight status in boys but not girls (this finding is the subject of a provocative article by Dr Arya Sharma, available here). Future work in the CHMS will look at how directly measured bouts of PA and sedentary time match up with self- and parent-report measures, as well as trying to determine when kids are most likely to be active or sedentary.
During the question/answer period, there was also an interesting discussion on the impact of basing PA guidelines on data that largely comes from self-report studies, and then evaluating whether people are meeting the guidelines using objective measures, given that the two types of data may not be readily comparable. This could have a large impact of policy decisions as well as public health messaging, and it’s a topic that probably warrants more attention than it has traditionally received, at least in the published literature.
Can we increase PA and reduce sedentary behaviour in preschoolers?
The second speaker was clinical psychologist Gary Goldfield, who discussed his recent work measuring and intervening on PA in young children. At present, 21% of Canadian pre-schoolers are overweight or obese (~6% are obese), while 90% of kids begin watching TV before the age of 2. Although we don’t have PA guidelines for pre-school kids here in Canada (yet), guidelines in other countries call for 3 hours of PA/day for this age-group (although very few children currently achieve this volume of PA).
While current PA levels in young children may not be very bright, Gary pointed out that day-care may provide an ideal opportunity for intervention, given that many children spend up to 10 hours/day in daycare. Thus he is currently overseeing a randomized controlled trial to see whether interventions aimed at increasing PA and improving food choices in the daycare setting results in tangible benefits. Although data is still coming in, the results are very promising with respect to BMI and fat mass and modestly promising with respect to activity levels (especially over the short term), although data related to motor skill development appeared less promising.
Do obese kids work as hard as they think?
The third presentation was from Dr Kristi Adamo, who discussed her experience overseeing CHEO’s Pediatric Obesity Cohort – an indepth longitudinal study of physical activity, body composition and health in children with severe obesity. As Dr Colley’s data would suggest, obese boys in Dr Adamo’s cohort were less active than their lean cohorts in the general population, while there was no difference in girls. However, the obese participants in this cohort were no more sedentary than lean peers from the general population, which is not what I would have expected.
The title of Kristi`s talk comes from her work looking at the level of perceived exertion in obese youth during exercise, in comparison to their lean counterparts. Perceived exertion is a self-reported measure, where a person is asked to describe how hard they are working, using a 20-point scale ranging from “very light” to “very high”. In Kristi’s cohort, this was assessed during a maximal fitness test, at the same time as directly measured oxygen consumption and carbon dioxide excretion (this allows for the self-reported and directly measured data to be directly compared). Contrary to what some might expect, these kids were actually very accurate in describing how hard they were working (e.g. when they said they were working near their max, this was supported by directly-measured assessments of oxygen consumption). And so, in response to the title question – yes, obese kids are working as hard as they think.
Kristi also made some very prescient comments about the potential side effects of maximal exercise testing – kids typically hate doing maximal treadmill testing (as do most people). As a result, this type of maximal testing may inadvertently turn kids off from further exercise, because they may associate physical activity with the unpleasantness of their max-testing. I`ve heard other researchers make similar comments at other conferences, and I think it`s worth considering for people who work in the pediatric population, and especially those at risk for low levels of physical activity.
You can read more about Kristi and Gary`s interesting work on the ability of active gaming to promote physical activity in teens with obesity in this previous post (hint: it wasn’t very useful).
Do all sedentary behaviours lead to weight gain? Sleep does not
The final presentation was given by Dr Jean-Philippe (JP) Chaput, who has done several studies on the health effects of various types of sedentary behaviour. Some of Dr Chaput`s most interesting work was on the impact of mental work and video-game playing on food intake. Compared to sitting quietly, he has found that both mental work and video-game playing increase food intake (to the tune of roughly 230 calories per meal), despite having no effect on energy expenditure. Other work has shown that listening to music and watching television during eating can also significantly increase food intake. Given the impact of sedentary behaviour on food intake, it is entirely possible that sedentary behaviour may influence energy intake more than energy expenditure (discussed previously by Dr Arya Sharma here).
Finally, JP concluded his talk by looking at the impact of sleep duration, which he has found consistently predicts the risk of obesity and food intake. In contrast to other sedentary behaviours, people who get more sleep are at less risk of obesity, while short-term sleep deprivation results in increased food intake. This is one of the reasons why I’m in favour of restricting the definition of sedentary behaviours to waking activities, as sleep appears to have health impacts which directly oppose those of waking sedentary behaviours.
That was my experience at the first full day of CSEP 2011 here in Quebec City. Tomorrow (Friday) I will be presenting my own data on the impact of acute exercise on health in abdominally obese men. Hope to see some of you there!