Elsevier

Preventive Medicine

Volume 47, Issue 5, November 2008, Pages 463-470
Preventive Medicine

Review
A review of mediators of behavior in interventions to promote physical activity among children and adolescents

https://doi.org/10.1016/j.ypmed.2008.07.011Get rights and content

Abstract

Background

The effectiveness of interventions to promote physical activity in youths is still developing. To develop a better understanding “what works”, researchers are now focusing on constructing an evidence base for mediators of behavior change.

Methods

We reviewed studies that examined the direct effect of physical activity interventions on hypothesized mediators and the relationship between mediators and physical activity in young people (aged 5 to 18 years). Studies were identified via electronic database searches and scanning references against predetermined quality criteria.

Results

We found seven studies that evaluated three mediator groups: cognitive, behavioral and interpersonal mediators. Self-efficacy was the most commonly assessed mediator in youth interventions and there was strong support for its role in mediating the relation between theory-based interventions and physical activity. There was some support for the importance of behavioral strategies as mediators of behavior, but no support for the mediating influence of interpersonal factors.

Conclusions

Despite recognition of the importance of mediation studies, few interventions have assessed mediators of physical activity behavior in youth interventions. The small number of studies examining mediators of behavior and the variability in study design and quality prevent us from forming strong conclusions regarding the most effective mediators of behavior.

Introduction

Due to the benefits of physical activity and concern regarding low levels of activity, numerous interventions targeting activity behavior in youth have been evaluated. However, the majority of these studies have produced modest results (Stone et al., 1998, Van Sluijs et al., 2007). It has been suggested the lack of effectiveness of youth interventions is, in part, due to a poor understanding of the mechanisms responsible for behavior change (Baranowski and Jago, 2005). While interventions are generally developed in reference to a theory of health behavior change (e.g., Social Cognitive Theory, Theory of Planned Behavior), few studies have examined possible mediators in effective interventions (Baranowski et al., 1998). In 2002, Lewis et al. (2002) published an important review of psychosocial mediators of physical activity behavior and found only two studies that examined mediators in youth interventions.

A mediator can be defined as an intervening causal variable necessary to complete the pathway from an intervention to the targeted behavioral outcome (Bauman et al., 2002). Measurement of these change mechanisms is necessary for the systematic progression of physical activity research (Bauman et al., 2002) because it allows researchers to determine which components of an intervention contribute to behavior change. Furthermore, mediation analyses allow researchers to develop more parsimonious models by eliminating unrelated mediators from future interventions (MacKinnon and Dwyer, 1993).

Randomized controlled trials are regarded as the ‘gold standard’ for physical activity intervention design and they also provide a valuable opportunity for the identification of mediators of behavior change (Kraemer et al., 2002). In its simplest form, testing for mediating effects is accomplished by adding a mediating variable (e.g., self-efficacy) to the regression equation of the independent (e.g., intervention condition) and dependent variables (e.g., physical activity) (MacKinnon et al., 2007) (Fig. 1). In mediational hypotheses, it is assumed that the inclusion of a mediating variable will reduce the magnitude of the relationship between the independent and dependent variables (MacKinnon et al., 2000). However, suppression occurs when the inclusion of an additional variable (e.g., mediator) increases the predictive validity of another variable (e.g., intervention) by its inclusion in an equation (Tzelgov and Henik, 1991). There are three major approaches used to establish statistical mediation, these include the causal steps as proposed by Baron and Kenny (1986), the difference in coefficients and the product of coefficients (MacKinnon, 2000). These methods are described in detail by MacKinnon et al. (2007).

While studies often cite a theoretical framework for their intervention, they rarely test the efficacy of these models using appropriate strategies (Baranowski et al., 1998). For example, a study might report the effect of an intervention on hypothesized mediators or psychosocial constructs (e.g., Deforche et al., 2004, Parcel et al., 1989, Simon et al., 2004), without examining potential mediation pathways. This type of analysis does not establish that changes in the theoretical constructs were responsible for changes in the outcome variable. The aim of this paper is to review the evidence of mediators of physical activity behavior change in youth interventions because such an analysis should further our understanding of intervention effectiveness.

Section snippets

Identification of studies

A comprehensive search of published studies was conducted using the computer databases PubMed, Embase, PsychINFO and SPORTS Discus. Experts in the field were contacted and the following hand selected scientific journals were searched Psychology of Sport and Exercise, Journal of Sport and Exercise Psychology, Preventive Medicine and Health Psychology. The key terms for searches included mediation, mediator, intervention, and physical activity. Titles, references, and abstracts of articles

Overview of study quality

We found seven studies examining potential mediators of physical activity behavior change in youth, spanning three types of mediating variables-cognitive, interpersonal and behavioral. All of the studies were conducted in secondary schools. Studies were from four countries, Belgium, Iran, the United States of America (USA) and United Kingdom (UK). The sample sizes of the interventions ranged from 78 to 2840 participants. The shortest assessment period was 3 months and the longest was 2 years.

Discussion

Mediation analyses from intervention studies provide researchers, health promoters and educators with evidence about ‘what works’ for changing physical activity behaviors. The aim of our review was to identify mediators of physical activity behavior in youth. Only seven studies satisfied the criteria for inclusion in this review and due to the diversity of interventions, methods, and findings, conclusions are difficult to draw. The majority of studies involved adolescent girls and because

Conflict of interest statement

The authors have no conflict of interest to declare.

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