What works in school-based energy balance behaviour interventions and what does not? A systematic review of mediating mechanisms

Special Issue of Journal of Applied Physiology Focusing on Sedentary Behaviour
October 11, 2011
Does exposure to fast-paced television reduce cognitive function in young children?
October 25, 2011
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Beginning this week, SBRN is pleased to host weekly summaries of peer-reviewed research in the area of sedentary behaviour, written by graduate students and young investigators working in a range of disciplines. Information on the author of today’s article can be found at the bottom of this post.  If you are interested in writing a summary of an article that you found interesting, please contact us here.

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Introduction

The ever present public health challenge of obesity has placed a great deal of focus upon energy balance related behaviours, such as sedentary behaviour. If negative energy balance is to be achieved effective modification of physical activity, sedentary behaviour and dietary habits is required. As evidence for the impact of school-based energy balance behaviour interventions is equivocal, identification of effective intervention mechanisms (i.e. theoretical mediating variables) is important. There appears to be plentiful research on variables related to physical activity, sedentary behaviour and dietary habits, but much less upon variables that are shown to be causally related to behaviour change (mediating variables). This study therefore aimed to identify psychosocial and environmental mediators (causal variables) of energy-balance behaviour interventions in children and adolescents. As this is the Sedentary Behaviour Research Network I’ll concentrate only on findings regarding sedentary behaviour.

What did they do?

The authors systematically searched five electronic databases with terms for energy balance behaviours, mediating variables and intervention/promotion studies. Studies were included if they were school-based RCT’s or quasi-experimental studies, targeted one of the three energy balance behaviours, and had conducted mediation analyses (among other criteria). The metholodigical quality of studies was assessed against 10 criteria, and evidence was ranked as strong, moderate, or insufficient by taking into account the number, metholodigical quality and consistency of outcomes of the studies. All told a fairly standard and rigorous review of pertinent literature.

What did they find?

The authors were interested in three concepts a) did the intervention (e.g. education sessions) change the theoretically proposed mediating variable? (e.g. attitude towards reducing TV time) b) is there a relationship between change in the proposed mediating variable (e.g. attitude towards reducing TV time) and change in the outcome variable (e.g. time spent watching TV?) regardless of whether the participant received the intervention or not?; and c) the extent to which the intervention changed the mediating variable and the impact this had on the sedentary behaviour outcome.

From ten studies (that focused solely on sedentary behaviour) reviewed the authors found no significant effect for the interventions upon the variables of attitude, self-efficacy, social norms or habit strength. They did however find a significant intervention effect upon intrinsic-motivation in one TV viewing intervention study. Negative relationships were seen between change in attitude, self-efficacy, and intrinsic motivation and screen-viewing, and a positive relationship between change in habit strength and screen viewing suggesting that targeting these variables may lead to decreased screen time (note: this is only an association). Contrary to what you would expect, change in social norms (e.g. parental thoughts, and encouragement towards reduced screen-viewing) in both boys and girls was positively related to screen-viewing.

Most studies did not find a significant impact of the interventions themselves on sedentary behaviour, and therefore did not report whether a change in the mediating variable led to a change in sedentary behaviour. Studies that did report mediation effects did not see any impact of intrinsic motivation or intervention-related concepts (e.g. incentives for children) on screen viewing.

What’s the take-home message?

It seems our knowledge of how to change sedentary behaviour is quite limited! There were negative associations between change in attitudes towards screen-viewing, self-efficacy, intrinsic motivation and measures of screen-viewing and TV-viewing in both boys and girls. These may therefore be useful variables to target in future sedentary interventions; such studies should examine if these are mediators of change in sedentary behaviour interventions. Interestingly the authors speculate that dissimilar to physical activity, sedentary behaviours may not be the consequence of forethought and planning:

Rather than being influenced by conscious cognitions, sedentary behaviour may instead be influenced by individual biological factors, habit strength and parental factors.

Clearly there is plentiful scope to contribute to our understanding of what the mediating effects of other correlates of sedentary behaviour are in sedentary behaviour interventions; particular examples given by the authors of this paper include parental rules and number of TV’s in the household. Other examples might include parental concern for child TV viewing (especially as change in social norms were positively related to screen-viewing) which was found to be positively associated with TV viewing in a recent paper in IJBNPA (Pearson et al., 2011). It appears more studies are needed by those clever behavioural scientists….

Van Stralen, M.M., Yildirim, M., Te Velde, S.J., Brug, J., Van Mechelen, W., & Chinapaw, M.J.M. (2011). What works in school-based energy balance behaviour interventions and what does not? A systematic review of mediating mechanisms. International Journal of Obesity, 35, 1251-1265.

 

Ash Routen

About the author: Ash Routen is in the final months of his doctoral studies at the University of Worcester, UK examining the impact of pedometer interventions on habitual PA in kids, with an interest in the assessment of body composition and objective physical activity measurement in kids.  He can be found on Twitter @AshRouten.

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