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Mediators of physical activity behaviour change among adult non-clinical populations: a review update

Mediators of physical activity behaviour change among adult non-clinical populations: a review... Background: An understanding of the determinants of physical activity through mediators of behaviour change is important in order to evaluate the efficacy of interventions. Prior reviews on this topic noted that few studies employed mediator analyses in experimental physical activity trials; the purpose of this review is to update these prior reviews in order to evaluate the state of our present understanding of interventions that include proposed mediators of behaviour change. Methods: Literature was identified through electronic database (e.g., MEDLINE, psychINFO) searching. Studies were eligible if they described a published experimental or quasi-experimental trial examining the effect of an intervention on physical activity behaviour and mediator change in non-clinical adult populations. Quality of included studies was assessed and the analyses examined the symmetry between mediators and behaviour change. Results: Twenty seven unique trials passed the eligibility criteria and 22 were included in the analysis with scores of moderate or higher quality. Half of the studies reviewed failed to show an intervention effect on PA. The remaining studies showed evidence that the intervention affected changes in the proposed mediators, but tests of mediated effect were performed in only six of these 11 cases and demonstrated mixed outcomes. Differences by theory were not discernable at this time, but self-regulation constructs had the most evidence for mediation. Conclusion: Published literature employing mediators of change analyses in experimental designs is still relatively elusive since the time of prior reviews; however, the general null findings of changes in mediating constructs from these interventions are a more timely concern. Changes in self-regulation constructs may have the most effect on changes in PA while self-efficacy and outcome expectation type constructs have negligible but limited findings. Innovation and increased fidelity of interventions is needed and should be a priority for future research. Introduction authors showed that interventions had weak evidence in The health benefits of regular physical activity (PA) are their capability to make behavioural changes at recom- well-established and convincing [1], yet at least half of the mended guideline values. Thus, there is a need to hone populace fail to meet national recommended guidelines existing interventions and to make effective and innova- [2]. As a result, the promotion of PA is of great impor- tive changes. tance to public health. Intervention efforts have met with At the forefront of these considerations is the applica- very modest success in changing PA [3,4]. For example, a tion of sound behavioural theory when designing inter- meta-analysis of PA intervention studies conducted by ventions [6]. There has been a proliferation of Hillsdon et al., reports an overall change in behaviour of correlation-based theory testing in the general health .31 SD, an effect size that is considered very small by gen- behaviour domain with recent advocacy for experimental erally accepted behavioural standards [5]. Further, the testing [7,8]. Although such tests are undoubtedly essen- tial to establishing the internal validity of a theory, they * Correspondence: [email protected] also have important and immediate applied value to pub- Behavioural Medicine Laboratory, Faculty of Education, University of Victoria, Victoria, BC, Canada lic health promotion efforts. That is, the constructs used Full list of author information is available at the end of the article © 2010 Rhodes and Pfaeffli; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Com- mons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduc- BioMed Central tion in any medium, provided the original work is properly cited. Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 2 of 11 http://www.ijbnpa.org/content/7/1/37 in behavioural theories can help us understand "why" or also focused on PA as a form of primary prevention "why not" a PA intervention worked [3]. This seems among adults so only non-clinical populations were con- essential information in the designing of interventions; sidered. The strong recommendations for formal media- those PA promotion initiatives constructed to change tion analyses from these prior reviews coupled with now important target variables should then lead to desired a seven-year lag in time from the content of Lewis et al. behaviour change, while those interventions used to tar- [9] supports the need for a review update. get ineffective variables can be discarded. The heart of this argumentation is the assumption of a Method mediating framework between theoretical constructs and Eligibility criteria behaviour [3,9]. The assumption in behavioural theory is Eligible studies were published journal articles describing that interventions can target change in critical anteced- an experimental or quasi-experimental trial examining ents of behavioural engagement and these will follow a the effect of the theoretical intervention on physical causal chain to ensuing behaviour change. Specifically, activity behaviour change and on proposed mediating mediation is achieved with evidence of a significant and variables. Studies that investigated the relationship substantive product-of-coefficient estimate where the between the theoretical variables and the primary out- independent variable (e.g., intervention) has its effect on come of PA were also included. A study was excluded if it the outcome (e.g., change in PA) via the mediator [10,11]. examined child, adolescent, older adult (age 65+), or clin- Currently, behavioural theories/models such as social ical populations. Excluded studies were also those that (1) cognitive theory (SCT) [12], transtheoretical model examined adherence to PA behaviour or stage of change (TTM) [13], self-determination theory (SDT) [14], and only, (2) did not measure a change in mediating variables, theory of planned behaviour (TPB) [15] are the dominant (3) described only the process of the study without stating frameworks for mediating constructs in the PA domain. results, (4) used non experimental designs, or (5) were Reviews by Baranowski et al. [3] and Lewis et al. [9], written in any language other than English (see Addi- have focused on the evaluation of the mediating model in tional file 1). PA interventions. Overall, Baranowski and colleagues Search strategy noted several limits to the extant literature which were Literature searchers were conducted from January, 1998 subsequently mirrored in the 10 studies reviewed by to September, 2008 in ISI Web of Knowledge, SPORTDis- Lewis et al. Most strident was the finding that very lim- cus, psychINFO, and MEDLINE (see Additional file 2). ited literature had tested the proposed mediating mecha- The electronic search strategy was developed by both nisms with a formal statistical test such as those outlined authors and was based on Baranowski et al. [3] and Lewis in Baron and Kenny [16] and more recently the product- et al.'s [9] previous studies examining mediating variables of coefficient tests recommended by MacKinnon and col- in physical activity interventions. A combination of key- leagues [10]. This information is considered essential for words were used, including physical activity, exercise, convincing evidence of the causal chain between inter- physical fitness, psychological theory, psychosocial corre- vention, theory, and behaviour change. Thus both groups lates, intervention, social cognitive theory, transtheoreti- of authors concluded that more research employing for- cal model, theory of planned behaviour, self- mal mediating analyses need to be conducted. Lewis et al. determination theory, protection motivation theory, noted in their evaluation of SCT and the TTM that the behavioural research, theoretical effectiveness, behaviour behavioural processes of change (i.e., self-regulatory change, health behaviour, mediator, self-efficacy, cogni- actions such as planning, using reinforcements, and cues, tive, stage of change, and process of change. The search etc.) had the most convincing and reliable evidence as a was executed by one author (LP). The search was not mediator from interventions, but noted that the evidence restricted by language, study design, or population. Man- was still limited. Several tests of interventions and media- ual cross-referencing of bibliographies was also com- tors showed mixed or even null relationships with the pleted. intervention and PA behaviour in these reviews. Further, no examination of other leading theories such as SDT or Screening the TPB was conducted in their review. Citations were screened by two reviewers (LP, RR) using Thus, the purpose of this review was to provide an pre-defined inclusion criteria. Studies were initially update of the literature on behavioural mediators of PA screened based on the title and abstract. Relevant interventions since the time of these prior reviews and abstracts were then selected for a full read of the article. include all resulting theories applied to PA. The review is Potential studies for adjudication were examined by two Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 3 of 11 http://www.ijbnpa.org/content/7/1/37 reviewers (RR and LP). It was then determined whether theory test examines whether the intervention was able the study met the criteria and was included in the review. to change the proposed mediator; the conceptual theory Consensus was reached in 100% of the cases. test examines whether intervention-induced changes in the outcome (PA) are attributable the mediator, and the Data abstraction simultaneous test of both represents an evaluation of the The two authors abstracted data using a pre-specified 12 extent to which the intervention effect was mediated by item data abstraction form (see Additional files 3 and 4). the mechanisms hypothesized to cause changes in PA. A The abstracted data included authors, sample, study liberal coding for each theory was applied where support design and setting, PA target, dependent variables, inter- for a test was obtained for at least one construct/behav- vention theory, intervention length and characteristics, iour at one time point. This was deemed a valid assump- measurement tools, outcomes, and mediator analysis. tion because all of the above noted theories/models are multivariate in nature and do not stipulate that all of their Analysis methods constructs necessarily function in tandem. Decision pro- Studies were grouped in total and by SCT [17], the TTM cedures were based on significant/null findings (p < .05) [13], TPB [18], protection motivation theory (PMT) [19], in each study as well as the establishment of at least a and SDT [14] based on a priori classification of psycho- small effect size using standardized criteria [5] (d > .19; η logical theories [9]. A more specific grouping was also > .009). conducted at the construct level across theories. Some Narrative appraisal and evidence synthesis were subse- prominent theorists have suggested that popular theories quently performed [24]. Key factors for consideration in of health behaviour have considerable conceptual overlap this qualitative appraisal included the success or failure of among their constructs [6,12,18,20]. Using these taxono- the action, theory, and simultaneous tests, as well as prior mies as a guide, constructs of self-efficacy/control (i.e., review results [9]. Typical interpretations of risk versus self-efficacy, perceived behavioural control), outcome harm in outcome research [24] do not translate to the expectations (outcome expectations, attitude/behavioural topic of mediators perfectly; evidence was thus classified beliefs, pros, cons, response efficacy, vulnerability, sever- by 1) weak or no evidence for mediation, 2) mixed evi- ity), self-regulatory processes or goals (intention, plan- dence for mediation, or 3) strong evidence for mediation. ning, goals, self-regulation, behavioural processes) and social expectancies (social support, subjective norm) Results were included. The literature search yielded a total of 6620 potentially Study quality was assessed using the checklist tool relevant records. Of these, 359 abstracts and full text developed specifically for mediator analyses by Lubans, Foster and Biddle [21] and three additional items (i.e., measure reliability, appropriate analysis methods, assess- PotentiallyrelevantcitationsidentifiedfromISI ment of change in mediator preceding change in the out- WebofKnowledge,MEDLINE,psychINFO,and come) from Cerin and colleagues [22]. The tool was SPORTDiscus(N=6608) created with similar scoring to the Cochrane Collabora- Citationsidentifiedthroughothersources (N=12) tion's instrument for assessing risk of bias [23] and Numberofduplicatescitations includes 11 questions answered with a yes (1) or no (0) removed(N=3970) format. High quality is considered with scores of nine to Potentiallyrelevantcitationsscreened 11, moderate quality was considered with scores of five to (N=2650) eight and low quality was considered with scores of zero Citationsexcluded(N=2291) to four. Following the suggestions of the Grade Working Reasons:irrelevanttoreview (N=2291) Group [24], the overall quality of the studies was reported to describe the general state of research on the topic and Potentiallyappropriatecitationstobe includedinthereview(N=359) this included low quality studies. This was followed by Citationsexcludedfromthereview (N=330) analyses of the high and moderate quality studies, how- Reasons:nonexperimental/weak ever, in order to make judgements with some protection design(N=117);PAchangenot from risk of bias [21,23]. reported(N=41);mediatorvariables notexamined(N=76);dissertations, Studies were coded by whether the intervention was thesis,andabstracts(N=33);clinical population(N=26);noresults effective in changing behaviour and subsequently with an reported(N=18);other(N=19) approach used by Cerin and colleagues [22] that outlines Studiesincludedinthereview(N=29) mediator models by tests of action theory, conceptual Uniquetrialsincludedinthereview(N=27) theory, and simultaneous test of both action and concep- tual theories (i.e., mediated effect). Specifically, the action Figure 1 Results of the Literature Search. Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 4 of 11 http://www.ijbnpa.org/content/7/1/37 Table 1: Characteristics of Included Trial Reports (N = 27) Table 1: Characteristics of Included Trial Reports (N = 27) Characteristic Value Follow up test post 8 (29) intervention, N (%) Study Design PA target, N (%) Trial, N (%) 30 minutes MVPA most 17 (62) Randomized Control 16 (59) days/week Trial 30 minutes MVPA 3 4 (14) 2 group experimental 1 (3) days/week Quasi-experimental 4 (14) 20 minutes VPA 3 days/ 2 (7) Stratified Control Trial 1 (3) week Non random assignment 1 (3) Pre post test 4 (14) Outcome measures Arm, N (%) 3 Arm trial 7 (25) PA, N (%) 2 Arm trial 16 (59) PAR 7 (25) 4+ Arm trial 3 (11) GLTEQ 6 (22) Sample size, median (min, 150 (44, 31,420) CHAMPS 2 (7) max), N IPAQ 3 (11) Quality score, median (min, 6 (3, 7) SQUASH 1 (3) max) Objective measure 2 (7) Other self-report 7 (25) Participant population questionnaire No. of psychological 3 (1, 6) All Female trial, N (%) 7 (25) assessment tools, median Both gender trial, N (%) 20 (74) (min, max) Setting, N (%) Practice 4 (14) Reporting outcomes Home 2 (7) Work Site 3 (11) Change in PA behaviour, N 27 (100) (%) WIC 1 (3) Change in mediators, N (%) 27 (100) University 3 (11) Mediator analysis, N (%) 6 (22) Community 3 (11) Not reported 11 (40) Type of mediation test (N = 6) Intervention Baron and Kenny, N (%) 3 (50) Unspecified, N (%) 2 (33) Theory, N (%) Mackinnon et al., N (%) 2 (33) SCT 3 (11) Freedman-Schatzkin, N (%) 1 (16) TTM 9 (33) Bootstrap, N (%) 1 (16) PMT 2 (7) *note: some studies employed more than one type of test SDT 2 (7) TPB 3 (11) reports were obtained and reviewed. Twenty nine studies Duration, median (min, max), 12 (2, 104) describing 27 unique trials passed the eligibility criteria wk and were therefore included [25-52] (see Figure 1 based on QUOROM/PRISM guidelines [53]). These 27 trials were not included in the prior reviews on this topic [3,9]. Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 5 of 11 http://www.ijbnpa.org/content/7/1/37 Study characteristics the 11 samples demonstrating evidence that the interven- The 27 trials examined different types of interventions on tion had an action theory link. Of the remaining 11 sam- physical activity behaviour (see Tables 1 and Additional ples where the intervention demonstrated change in PA file 3). In terms of quality rating, five trials were identified [27,29-31,37,38,44,46-48,52], all showed evidence of an as low quality [33,39,42,45,54] and were not subsequently action test link, whereby at least some of the proposed included in the analyses (see Additional file 5). Of the mediating constructs changed from the intervention. remaining 22 trials, one was scored as high quality [44] These were not distinguishable by methodological char- and all others were deemed of moderate quality. Most acteristics. For example, studies ranged from college studies used constructs from a chosen theory with inten- undergraduates [46,48] to the general population [29,47] tions of increasing the participants' PA behaviour. The or specified populations [30,31]. Proposed mediators design of the interventions were either randomized con- included constructs from TTM [47], SCT [30], PMT [46], trol (N = 16), two group experimental (N = 1), quasi SDT [35], and TPB[48] and duration of the intervention experimental (N = 4), stratified control trial (N = 1), non ranged from two weeks [46] to one year [37]. Further, the random assignment (N = 1), or pre-post test (N = 4). Tri- interventions for these studies ranged from relatively als ranged from two to eight arms, with the majority straightforward messaging [46,48] to more intensive and using a two or three arm design comparing a high theo- long term counselling and workshops [30,31], while par- retical fidelity intervention to a standard public health ticipants ranged from carefully screened inactive samples intervention group (N = 20). Six other two arm studies [47] to no consideration of baseline physical activity [46] compared a high fidelity intervention to a control group. and comparisons were with true controls [48] or generic The settings of the studies included universities (N = 3), physical activity intervention groups [47]. general practice (N = 4), worksites (N = 3), and commu- Of these 11 studies to show evidence that the interven- nity settings (N = 3). Sample size ranged from 44 to tion could change PA and support the action test link, 31,420. Participants were of both genders (N = 20), or only five reported a conceptual theory test women only (N = 7). Physical activity was most com- [27,29,44,47,52], and six reported a mediator test monly assessed using IPAQ (N = 3), 7 day PAR (N = 8), [27,29,37,44,47,52]. All five conceptual theory tests and GLTEQ (N = 6). The interventions were based on showed at least some support for a link between a pro- SCT (N = 3), TTM (N = 9), TPB (N = 3), SDT (N = 2), and posed mediating construct and PA change, but the result- PMT (N = 2) among others. The interventions ranged in ing tests of mediation was supported in four [27,29,37,47] length from two weeks to 24 months. Nine studies had of the six samples. follow up tests from one month to one year after the end Evidence of Mediation by Theory of the intervention. The follow up tests ranged from short Transtheoretical Model interventions with long follow up periods (N = 2) to fol- Eight of the 22 samples employed constructs of the TTM low up tests with a length approximately equal to the as mediators of change (defined as including at least two length of the intervention period (N = 7); for example a 6 TTM constructs specified by Prochaska and DiClemente month intervention with a 6 month follow up. Interven- [55]) [28,31,32,34,36,44,47,56]. In all cases the studies tions examined the effects of counselling or group ses- were well-controlled designs where the TTM concepts sions (N = 11), telephone (N = 2) or email reminders (N = were employed in the interventions. One study, however, 5), print materials (N = 4), a combination (N = 4), and did not employ these interventions to standard control or other methods on PA levels and mediating variables. exercise prescription [36] and should be noted as deviant Most studies had a physical activity target set at 30 min- from the other eight studies. Furthermore, four of these utes of moderate intensity activity most days of the week eight studies reported a null effect of the intervention on (N = 15). Six studies set a target of three days of activity, PA change [28,32,36,49] and subsequent null action the- either vigorous (N = 2) or moderate (N = 4), while two ory tests on TTM constructs. The remaining four studies studies opted for a target of either 20 minutes of vigorous [31,44,47,52], however, all had evidence of at least one activity for three days per week, or 30 minutes of moder- TTM construct showing an action theory link. Three of ate activity for five days a week. these studies tested for a conceptual theory link with sig- General Evidence of Mediation nificant evidence for at least one TTM construct and Of the 22 samples, 11 did not show evidence that the these three studies also employed mediation effect tests intervention was effective in changing PA [44,47,52]. Interestingly, two of these studies demon- [25,26,28,32,36,40,41,43,49-51], thus failing the first con- strated that TTM mediators failed to attenuate the rela- sideration in most investigations/analyses of mediators tionship between the intervention and behaviour [44,52]. [11]. These studies generally had null results on the pro- By contrast, Napolitano et al. [47] demonstrated that posed mediators as well with only four [25,26,41,51] of behavioural processes of change (and cognitive processes Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 6 of 11 http://www.ijbnpa.org/content/7/1/37 as a suppressor) were able to account for the relationship constructs in a sample of undergraduate students between the intervention and behaviour in a formal although no formal conceptual theory test and mediation mediation test. Taken together, the TTM currently has analyses were conducted. Obviously the limited applica- mixed results in terms of intervention efficacy and in tions of PMT warrant more research. tests of mediation of its constructs. Self-Determination Theory Social Cognitive Theory Two studies have employed SDT (defined as including at Three studies have tested SCT (defined as including at least two constructs as specified by Deci and Ryan [14]) least two constructs as specified by Bandura [57]) in interventions using randomized experimental designs [30,37,51]. Two of the studies followed controlled trials in community samples [35,43]. Both studies employed [30,51], while the other employed a quasi-experimental interventions tailored to the concepts of SDT. Levy and design [37]. Furthermore, one [51] of these three studies Cardinal [43] employed a print mail-out intervention and did not support the effect of the intervention on behav- did not show changes in SDT constructs or behaviour, iour although all studies did have some support for an thus failing to support the action theory test and the link action theory link. None of the studies tested for a con- of the intervention to PA. By contrast, Fortier et al. [35], ceptual theory link, but Hallam and Petosa [37] provided used a primary care intervention setting and showed the evidence that self-regulation was a mediator of behaviour intervention had an effect on behaviour and an action at 12 months post-intervention, but did not show support theory link for SDT constructs of autonomy (motivation for self-efficacy or outcome expectations. It should be and support) but not competence. The investigators also noted that this mediation relationship was also inconsis- reported support for a conceptual theory link between tent and not present at six weeks or six month assess- autonomy support and PA but no formal tests of the ments and it did not examine mediation using product-of mediation effect was implemented. More research is coefficient tests recommended by MacKinnon and col- needed to evaluate SDT as a mediator of behaviour given leagues [10]. Thus, there is evidence for possible media- these limited findings. tion between selected SCT constructs and intervention- Evidence of Mediation by Construct PA change but the available studies are extremely limited Self-Efficacy/Perceived Control and mixed at present. Nineteen of the 22 studies employed a self-efficacy type Theory of Planned Behaviour construct, defined as an appraisal of confidence or capa- Three studies have employed the TPB (defined as includ- bility to perform physical activity. Of these, nine had null ing at least two constructs as specified by Ajzen [18]) effects of the intervention on PA change [40,48,50]. The methods for these studies include two [25,26,28,32,36,40,49-51] and only two of these showed experimental persuasive communication interventions support for subsequent action theory tests [25,26]. among undergraduates [40,48] and one quasi-experimen- Among the remaining 10 studies to support the initial tal community design [50]. Two of these studies, however, intervention-PA link, seven supported a significant show null results in terms of a link between the interven- action theory test for the effect of the intervention on tion and PA as well as the action theory test for a link changes in self-efficacy/control [27,30,38,46-48,52]. Four between the intervention and TPB constructs [40,50]. of these seven also reported conceptual model tests The single study [48] to show support for an effect of the [27,44,47,52] and three supported a link between changes intervention on changes in PA demonstrated action the- in self-efficacy/control and changes in PA [27,44,52]. Of ory links with intention, perceived behavioural control, the five studies that employed a formal mediation analysis and affective attitude (dependent on baseline values) yet [27,37,44,47,52], however, only one showed significant no conceptual theory test formal mediation analysis was support for self-efficacy [27]. In this case, Blanchard et al. performed. Overall, the evidence is too limited from a [27] demonstrated that task self-efficacy (efficacy to paucity of research and lack of actual behaviour change in physically perform the behaviour) was a significant medi- the interventions to make a judgement of the effective- ator of behaviour change but barrier self-efficacy (confi- ness of TPB as a mediator in PA interventions. dence to overcome hassles) was not. Thus, self-efficacy Protection Motivation Theory has considerably limited support for its role as a mediator Two studies have applied PMT (defined as including at of PA changes due to interventions at present. least two constructs as specified by Rogers [19]) [46,56]. Outcome Expectations Plotnikoff et al. [56], were unable to show effects of their Fourteen of the 22 studies reviewed included outcome work site intervention on the proposed mediators or expectations, defined broadly as expected/anticipated behaviour, thus failing to support the action theory test consequences from behavioural or lack of behavioural and the intervention-PA link. Milne et al. [46] showed engagement, as potential mediating constructs that their intervention had an effect on short-term PA [28,30,32,36,37,40,44,46-52]. Of these, seven showed null change and supported the action theory link for all PMT Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 7 of 11 http://www.ijbnpa.org/content/7/1/37 effects for the intervention on PA [28,32,36,40,49-51] and Social Constructs all but one of these [51] also reported non-significant Variables with social referents typically encompassed effects for the action theory test. Of the remaining seven either subjective norm (perceived pressure to perform studies, all but one [44] showed support for the action the behaviour) or social support (support from others to theory test of the intervention's effectiveness in changing perform the behaviour). Nine studies employed such outcome expectations. It is interesting to note that many variables in these studies [29,34,35,39,40,43,48,50,51] but of these studies measured and targeted outcome expecta- five of these studies did not show support for the effec- tions underlying the affective domain in the intervention tiveness of the intervention on changes in PA [40,43,49- (i.e., enjoyment, pain, fear) as opposed to more instru- 51] nor did they demonstrate significant action theory mental and distal outcome expectations (i.e., weight loss, tests on the social constructs. Three of the remaining fitness, chronic disease). Indeed, Parrott et al. [48] four studies showed significant action and conceptual showed a significant action theory test with affective out- theory tests and it is notable that all three studies contain come expectations but a non-significant action theory support rather than normative constructs [29,35,52]. test with instrumental outcome expectations when mea- Tests of the mediated effect, however, were conducted sured separately. Only three studies, however, reported among two of these studies and the results were mixed. subsequent conceptual theory tests [44,47,52], and the Specifically, Cerin and colleagues [29] demonstrated four tests to examine the mediation effect all reported mediation while Fahrenwald et al. [34] did not show evi- non-significant findings for outcome expectation con- dence for the mediation capacity of social support. Thus, structs [37,44,47,52]. Overall, there is limited evidence social constructs have some evidence for mediation of PA for outcome expectations as a mediator of PA interven- interventions and behaviour but results are limited and tions. Distinctions by affective/proximal and instrumen- positive findings have only been with support, not norms. tal/distal expectations in action theory tests suggest there may be more evidence for the affective/proximal domain Discussion in mediation but these studies did not report conceptual Theories of PA behaviour suggest that particular con- theory tests or specific mediated effects. structs are critical antecedents of behavioural engage- Self-Regulatory Processes ment. These constructs are hypothesized as components Defined generally as planning, scheduling, and self-orga- of a causal chain, suggesting that if the mediators are nizational behaviours, self-regulatory processes were changed, behaviour change should follow [6]. Early measured in some capacity in 16 of the 22 studies reviews based on theoretical mediators of behaviour [28,31,32,34,36-38,40,41,44,46-48,50,51,58]. Eight of change, however, suggested that few formal tests of medi- these studies showed null effects for the intervention on ation had been conducted and limited evidence was avail- behaviour change [28,32,36,40,41,49-51] and only two of able to support this proposition [3,9]. Therefore, the these had significant action theory tests [41,51] sugges- purpose of this review was to provide an update of the lit- tive of generally null/ineffective trials. Of the remaining erature on PA interventions that have included proposed eight studies, however, six reported evidence of signifi- mediators of behaviour, focusing specifically on primary cant action theory tests [37,44,46-48,52]. For example, prevention in adults since the time of these prior reviews. Milne et al. [46] showed that planning/implementation The review yielded 29 studies from 27 independent intentions affected increases in behaviour beyond those samples to appraise our current understanding of PA of an intervention that increased self-efficacy and out- mediators in interventions. Five studies were omitted come expectations. Despite these supportive action the- from the analyses due to low quality but the other 22 tri- ory tests, only three studies reported conceptual theory als showed moderate (n = 21) or high (n = 1) quality and tests, although all provided support for self-regulatory thus relatively low risk of bias. Almost all studies did not constructs [44,47,52]. Finally, of the four tests to examine meet the category for high quality because they failed to a mediated effect, Hallam and Petosa [37] and Napolitano include a direct measure of physical activity behaviour et al. [47], showed that changes in self-regulation (via self- and did not report on a pilot intervention to demonstrate regulation and behavioural processes of change respec- that it could affect the mediators. Otherwise, the 22 trials tively) mediated the relationship between the interven- generally showed many high quality features such as ran- tion and changes in PA. Still, there were two studies that dom assignment, a theoretical-base, reliable and valid demonstrated no mediation of a successful intervention measures of the mediators, and reliable measures of self- through self-regulation processes (behavioural processes) reported PA. [34,44]. Overall, there is some evidence for mediation Overall, 11 studies showed that the intervention had an between self-regulation processes and behaviour but effect on PA behaviour change and all of these studies results are mixed. subsequently had an action theory link [59]. That is, all 11 Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 8 of 11 http://www.ijbnpa.org/content/7/1/37 studies showed some evidence that the intervention also in PA; however, three of these four studies showed an changed the proposed mediators. By contrast, a concep- action theory link. Social support was also a mediator of tual theory link [59] was seldom reported (5/11 studies). behaviour change in one formal test of mediation, but Conceptual theory links demonstrate that changes in the was unable to show a mediated effect in the only other mediators are related to the PA outcome. These are often test with this construct. There was no evidence for the the foundation for using a theory or mediator construct mediation capacity of subjective norm. Although limited before initiation of the intervention [11], but future work literature precludes any definitive conclusions, social needs to test this link regularly in reported trials with constructs, particularly social support, may have utility as mediators. Formal tests of mediation were also only con- mediators of change but findings are mixed at present. ducted in six of the 11 cases where the procedure may A key finding of the review, however, was that half the have been appropriate (i.e., intervention effect on behav- interventions failed to change both behaviour and the iour, evidence of action theory link, conceptual theory proposed mediators through the action theory link. This link or probable conceptual theory link). In terms of does not challenge the internal structure of our leading behavioural mediation by theory, TTM, SCT, TPB, PMT, theories and constructs at present as much as demon- and SDT all showed some evidence for action theory tests strate that our interventions are generally ineffective. To and all have shown evidence for conceptual theory tests evaluate the mediation capacity of a theory, the behav- in the past, but only the TTM employed tests of a medi- ioural link and action link are important first steps in ated effect of its constructs. The results, when divided by mediation [11]. Pilot studies showing evidence that the theory, are too limited in number to make particular intervention can change the proposed mediators are rec- judgements at present. ommended in future research before large-scale trials are A division at the construct level [6,12,18,20], however, conducted. provides a larger sample for assessment. Self-regulation The poor performance of PA interventions has been constructs (e.g., planning, behavioural processes) from duly recognized [3,4], and it is much easier to comment trials where the intervention changed PA behaviour on this problem than to provide solutions. Nevertheless, showed 75% (6 of 8 studies) support for action theory it is important to provide some commentary on this issue. tests and all three of the conceptual theory tests con- A most pragmatic possibility for these results may be ducted were significant. Mediated effect tests of the con- attenuation from measurement error. For example, indi- struct, however, were mixed with two showing support rect (self-report) PA measures featured in these studies and two not providing evidence for mediation. Our may lack the sensitivity to distinguish change between the appraisal of self-regulation is similar to the original com- groups and the psychological constructs may equally lack ments made by Lewis et al. [9]; the construct has the most precision [3]. Direct measures of PA are recommended in support thus far but still demonstrates mixed findings. future trials. Still, this seems unlikely to be the sole reason Still, it seems prudent to include a self-management and for these null effects; many of the studies were able to self-regulatory component to PA interventions. demonstrate time effects (i.e., main effects), and the pro- Results of self-efficacy and outcome expectation-type posed mediators generally show moderate to large bivari- constructs as mediators were weak or limited. Self-effi- ate correlations with PA in prediction tests [e.g., [61]]. cacy constructs among intervention studies that affected Clearly more innovation and higher fidelity interven- PA change showed relatively strong evidence for action tions are needed. In the studies reviewed, there was a very theory (7 of 10 studies) and conceptual theory (3 of 4 similar genre of intervention. These typically focused on studies reported) links, but a mediated effect was not a persuasive educational component about the benefits of supported in four of the five formal tests conducted. Out- PA and hazards of inactivity followed by problem solving come expectation constructs had similar results in terms suggestions to regulate action and overcome barriers. of evidence for an action theory link (6/7 studies) but Although this approach could be helpful to some, it was zero of the four tests for a mediated effect were signifi- not helpful to change proposed mediators in over 50% of cant. There was some notable differences between affec- the cases reviewed and these null results were not readily tive and instrumental outcome expectations (see [60] for identifiable as discrepant intervention styles from suc- extended commentary) with positive changes in affective cessful trials. The problem occurring may be that the outcome expectations linked to positive changes in approach is an insufficient band-aid to overcome the real- behaviour more than instrumental outcome expectations. world obstacles and different values that some inactive Still, the relatively few studies on this topic and absence of participants experience. Social and environmental struc- any formal mediation tests render this point as specula- tures may be so grounded and geared to sedentary life- tive at present. styles that individual-level, inexpensive, patches may not Social constructs were limited to only four studies resonate with the inactive populace [41]. The limits of where the intervention had produced significant changes these "downstream" approaches have been recognized Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 9 of 11 http://www.ijbnpa.org/content/7/1/37 [62]. Approaches at system-level social and environmen- mediation. The general null findings of many behavioural tal change may be needed to aid many people [63]. This interventions are a timely concern. Innovation and approach, of course, is costly and does not lend itself to increased fidelity of interventions is needed and should the tight-budget three-year RCT; indeed, it is likely to be a priority for future research. conflict with other societal and industrial aims. Interacting with these more systemic social and envi- Additional material ronmental issues may be systemic internal issues. Enact- Additional file 1 Excluded articles. This file contains the list of articles ing a potentially fatiguing, boring, and time-consuming that did not meet our inclusion criteria. The articles are grouped based on behaviour on a repeated basis in the face of other behav- the criteria the articles failed to meet. ioural options and values is likely to pose an enormous Additional file 2 Search syntax. This file contains the search terms used daily challenge to many people. Some of this may arise in this review. Additional file 3 Review Table of proposed mediators and physical from differences in genetic predisposition and other indi- activity behavior. This file contains data extracted from each included arti- vidual differences that are not easily intervened upon cle in table form for quick reference. [64], while some of these decisions may be the result of Additional file 4 Data extraction. This file contains the data extracted informed free will. from each included article. Additional file 5 Quality of studies using tool developed by Lubans, When considering these possibilities, it seems impor- Foster, and Biddle (2008). This file contains the tool used to assess the tant for future interventions to become more innovative quality of each study included in the review. Each study was assessed by a and target proposed mediators with a higher fidelity. series of questions listed below. BMI: Body Mass Index; RCT: Randomized control trial; PA: physical activity; MI: motivational interviewing; ES: effect Using the tenets of SCT as a guide[57], the experiential size; OR: odds ratio; PAR: physical activity recall. T TM: transtheoretical model; qualities of the behaviour seem the most telling way to POC: processes of change; SCT: social cognitive theory; IPAQ: International affect cognitions rather than passive approaches. Experi- Physical Activity Questionnaire; GLTEQ: Godin Leisure Time Exercise Ques- tionnaire; SDT: self-determination theory; PMT: protection motivation the- ences of valued personal outcomes (e.g., enjoyment, plea- ory; TPB: theory of planned behaviour; PCB: perceived behavioural control; sure, satisfaction) and behavioural control/self-efficacy, CHD: coronary heart disease. through shifts in behavioural, environmental and social experiences of PA may be the most effective intervention Abbreviations SD: Standard Deviation; IPAQ: International Physical Activity Questionnaire; 7 alongside increasing self-regulatory skills. At this time, day PAR: 7 day Physical Activity Recall; GLTEQ: Godin Leisure Time Exercise we recommend that interventions focus on altering the Questionnaire; RCT: Randomized Control Trial; ES: Effect Size. behavioural experience in an attempt to improve fidelity Competing interests and affect change in proposed mediators. The authors declare that they have no competing interests. It is important to highlight the limitations of this review in order to provide a context for the results. First, the Authors' contributions RR conceived the review, participated in the coordination of the search, assessment is limited to published work and may be sub- assessed study quality, analyzed and interpreted the results, and drafted the ject to publication bias. Given the high rate of null effects majority of the manuscript. LP carried out the literature search, participated in in these results, the bias may be minimal but no formal the study quality assessment, compiled the results into tables, and drafted the methods section. Both authors read and approved the final manuscript. test of publication bias can be conducted. Second, the work contained in this review is limited to English writ- Authors' information ten journals and thus the results cannot generalize to RR, PhD, holds a Canadian Institutes for Health Research New Investigator Award and is currently an Associate Professor in the School of Exercise Science, studies conducted and published in other languages. Physical and Health Education at the University of Victoria. Finally, the review is limited to the search terms and data- LP, BPE/BEd, MA, is a Research Associate in the Behavioural Medicine Labora- bases contained in our methods section, which followed tory at the University of Victoria. the precedent of Baranowski et al. [3] and Lewis et al. [9]. Acknowledgements Studies that have not been abstracted with these key Production of this paper has been made possible through a financial contribu- words will be missing from our review. tion from the Public Health Agency of Canada. The views expressed herein do not necessarily represent the views of the Public Health Agency of Canada. We also acknowledge the helpful comments from Andrea Tricco and Michelle Kho. Conclusions In summary, less than half of the 22 studies reviewed Author Details showed evidence that the intervention changed PA and 1 Behavioural Medicine Laboratory, Faculty of Education, University of Victoria, Victoria, BC, Canada and School of Exercise Science, Physical and Health the proposed meditating constructs of behaviour. Among Education, University of Victoria, Victoria, BC, Canada the studies to show these effects, about half subsequently performed tests of the mediating effect or that changes in Received: 21 July 2009 Accepted: 11 May 2010 Published: 11 May 2010 the proposed mediator were linked to changes in PA. T © T In h h t2 i i e s s 0 rn arti i1 sa 0 an t R io cle h O na o i p d s l J e ava es n o a A ur n icce lable na d Pf l o ss arti a f f B e ro ff em ha lcl i; l :e h v ic d io ttp:/ ei rn s a t s lri ee N /bu w u B w tte riit o w d iM o .i u jbn n ed C n a d n p e d a e r th P .n ot h rre g ys a te / lic Lt co rm an d. l A ts e c o n tif t/ v th i7/ tye 1/ 2010, C 37 reati 7 ve :37 Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tests of mediated effect also showed mixed outcomes. Differences by theory were not discernable at this time, but self-regulation constructs had the most evidence for Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 10 of 11 http://www.ijbnpa.org/content/7/1/37 References 27. Blanchard CM, Fortier M, Sweet S, O'Sullivan T, Hogg W, Reid RD, Sigal RJ: 1. 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Rhodes RE: The built-in environment: The role of personality with physical activity. Exercise and Sport Sciences Reviews 2006, 34:83-88. doi: 10.1186/1479-5868-7-37 Cite this article as: Rhodes and Pfaeffli, Mediators of physical activity behav- iour change among adult non-clinical populations: a review update Interna- tional Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Behavioral Nutrition and Physical Activity Springer Journals

Mediators of physical activity behaviour change among adult non-clinical populations: a review update

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Copyright © 2010 by Rhodes and Pfaeffli; licensee BioMed Central Ltd.
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Chemistry; Nutrition; Behavioral Sciences; Health Promotion and Disease Prevention
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Abstract

Background: An understanding of the determinants of physical activity through mediators of behaviour change is important in order to evaluate the efficacy of interventions. Prior reviews on this topic noted that few studies employed mediator analyses in experimental physical activity trials; the purpose of this review is to update these prior reviews in order to evaluate the state of our present understanding of interventions that include proposed mediators of behaviour change. Methods: Literature was identified through electronic database (e.g., MEDLINE, psychINFO) searching. Studies were eligible if they described a published experimental or quasi-experimental trial examining the effect of an intervention on physical activity behaviour and mediator change in non-clinical adult populations. Quality of included studies was assessed and the analyses examined the symmetry between mediators and behaviour change. Results: Twenty seven unique trials passed the eligibility criteria and 22 were included in the analysis with scores of moderate or higher quality. Half of the studies reviewed failed to show an intervention effect on PA. The remaining studies showed evidence that the intervention affected changes in the proposed mediators, but tests of mediated effect were performed in only six of these 11 cases and demonstrated mixed outcomes. Differences by theory were not discernable at this time, but self-regulation constructs had the most evidence for mediation. Conclusion: Published literature employing mediators of change analyses in experimental designs is still relatively elusive since the time of prior reviews; however, the general null findings of changes in mediating constructs from these interventions are a more timely concern. Changes in self-regulation constructs may have the most effect on changes in PA while self-efficacy and outcome expectation type constructs have negligible but limited findings. Innovation and increased fidelity of interventions is needed and should be a priority for future research. Introduction authors showed that interventions had weak evidence in The health benefits of regular physical activity (PA) are their capability to make behavioural changes at recom- well-established and convincing [1], yet at least half of the mended guideline values. Thus, there is a need to hone populace fail to meet national recommended guidelines existing interventions and to make effective and innova- [2]. As a result, the promotion of PA is of great impor- tive changes. tance to public health. Intervention efforts have met with At the forefront of these considerations is the applica- very modest success in changing PA [3,4]. For example, a tion of sound behavioural theory when designing inter- meta-analysis of PA intervention studies conducted by ventions [6]. There has been a proliferation of Hillsdon et al., reports an overall change in behaviour of correlation-based theory testing in the general health .31 SD, an effect size that is considered very small by gen- behaviour domain with recent advocacy for experimental erally accepted behavioural standards [5]. Further, the testing [7,8]. Although such tests are undoubtedly essen- tial to establishing the internal validity of a theory, they * Correspondence: [email protected] also have important and immediate applied value to pub- Behavioural Medicine Laboratory, Faculty of Education, University of Victoria, Victoria, BC, Canada lic health promotion efforts. That is, the constructs used Full list of author information is available at the end of the article © 2010 Rhodes and Pfaeffli; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Com- mons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduc- BioMed Central tion in any medium, provided the original work is properly cited. Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 2 of 11 http://www.ijbnpa.org/content/7/1/37 in behavioural theories can help us understand "why" or also focused on PA as a form of primary prevention "why not" a PA intervention worked [3]. This seems among adults so only non-clinical populations were con- essential information in the designing of interventions; sidered. The strong recommendations for formal media- those PA promotion initiatives constructed to change tion analyses from these prior reviews coupled with now important target variables should then lead to desired a seven-year lag in time from the content of Lewis et al. behaviour change, while those interventions used to tar- [9] supports the need for a review update. get ineffective variables can be discarded. The heart of this argumentation is the assumption of a Method mediating framework between theoretical constructs and Eligibility criteria behaviour [3,9]. The assumption in behavioural theory is Eligible studies were published journal articles describing that interventions can target change in critical anteced- an experimental or quasi-experimental trial examining ents of behavioural engagement and these will follow a the effect of the theoretical intervention on physical causal chain to ensuing behaviour change. Specifically, activity behaviour change and on proposed mediating mediation is achieved with evidence of a significant and variables. Studies that investigated the relationship substantive product-of-coefficient estimate where the between the theoretical variables and the primary out- independent variable (e.g., intervention) has its effect on come of PA were also included. A study was excluded if it the outcome (e.g., change in PA) via the mediator [10,11]. examined child, adolescent, older adult (age 65+), or clin- Currently, behavioural theories/models such as social ical populations. Excluded studies were also those that (1) cognitive theory (SCT) [12], transtheoretical model examined adherence to PA behaviour or stage of change (TTM) [13], self-determination theory (SDT) [14], and only, (2) did not measure a change in mediating variables, theory of planned behaviour (TPB) [15] are the dominant (3) described only the process of the study without stating frameworks for mediating constructs in the PA domain. results, (4) used non experimental designs, or (5) were Reviews by Baranowski et al. [3] and Lewis et al. [9], written in any language other than English (see Addi- have focused on the evaluation of the mediating model in tional file 1). PA interventions. Overall, Baranowski and colleagues Search strategy noted several limits to the extant literature which were Literature searchers were conducted from January, 1998 subsequently mirrored in the 10 studies reviewed by to September, 2008 in ISI Web of Knowledge, SPORTDis- Lewis et al. Most strident was the finding that very lim- cus, psychINFO, and MEDLINE (see Additional file 2). ited literature had tested the proposed mediating mecha- The electronic search strategy was developed by both nisms with a formal statistical test such as those outlined authors and was based on Baranowski et al. [3] and Lewis in Baron and Kenny [16] and more recently the product- et al.'s [9] previous studies examining mediating variables of coefficient tests recommended by MacKinnon and col- in physical activity interventions. A combination of key- leagues [10]. This information is considered essential for words were used, including physical activity, exercise, convincing evidence of the causal chain between inter- physical fitness, psychological theory, psychosocial corre- vention, theory, and behaviour change. Thus both groups lates, intervention, social cognitive theory, transtheoreti- of authors concluded that more research employing for- cal model, theory of planned behaviour, self- mal mediating analyses need to be conducted. Lewis et al. determination theory, protection motivation theory, noted in their evaluation of SCT and the TTM that the behavioural research, theoretical effectiveness, behaviour behavioural processes of change (i.e., self-regulatory change, health behaviour, mediator, self-efficacy, cogni- actions such as planning, using reinforcements, and cues, tive, stage of change, and process of change. The search etc.) had the most convincing and reliable evidence as a was executed by one author (LP). The search was not mediator from interventions, but noted that the evidence restricted by language, study design, or population. Man- was still limited. Several tests of interventions and media- ual cross-referencing of bibliographies was also com- tors showed mixed or even null relationships with the pleted. intervention and PA behaviour in these reviews. Further, no examination of other leading theories such as SDT or Screening the TPB was conducted in their review. Citations were screened by two reviewers (LP, RR) using Thus, the purpose of this review was to provide an pre-defined inclusion criteria. Studies were initially update of the literature on behavioural mediators of PA screened based on the title and abstract. Relevant interventions since the time of these prior reviews and abstracts were then selected for a full read of the article. include all resulting theories applied to PA. The review is Potential studies for adjudication were examined by two Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 3 of 11 http://www.ijbnpa.org/content/7/1/37 reviewers (RR and LP). It was then determined whether theory test examines whether the intervention was able the study met the criteria and was included in the review. to change the proposed mediator; the conceptual theory Consensus was reached in 100% of the cases. test examines whether intervention-induced changes in the outcome (PA) are attributable the mediator, and the Data abstraction simultaneous test of both represents an evaluation of the The two authors abstracted data using a pre-specified 12 extent to which the intervention effect was mediated by item data abstraction form (see Additional files 3 and 4). the mechanisms hypothesized to cause changes in PA. A The abstracted data included authors, sample, study liberal coding for each theory was applied where support design and setting, PA target, dependent variables, inter- for a test was obtained for at least one construct/behav- vention theory, intervention length and characteristics, iour at one time point. This was deemed a valid assump- measurement tools, outcomes, and mediator analysis. tion because all of the above noted theories/models are multivariate in nature and do not stipulate that all of their Analysis methods constructs necessarily function in tandem. Decision pro- Studies were grouped in total and by SCT [17], the TTM cedures were based on significant/null findings (p < .05) [13], TPB [18], protection motivation theory (PMT) [19], in each study as well as the establishment of at least a and SDT [14] based on a priori classification of psycho- small effect size using standardized criteria [5] (d > .19; η logical theories [9]. A more specific grouping was also > .009). conducted at the construct level across theories. Some Narrative appraisal and evidence synthesis were subse- prominent theorists have suggested that popular theories quently performed [24]. Key factors for consideration in of health behaviour have considerable conceptual overlap this qualitative appraisal included the success or failure of among their constructs [6,12,18,20]. Using these taxono- the action, theory, and simultaneous tests, as well as prior mies as a guide, constructs of self-efficacy/control (i.e., review results [9]. Typical interpretations of risk versus self-efficacy, perceived behavioural control), outcome harm in outcome research [24] do not translate to the expectations (outcome expectations, attitude/behavioural topic of mediators perfectly; evidence was thus classified beliefs, pros, cons, response efficacy, vulnerability, sever- by 1) weak or no evidence for mediation, 2) mixed evi- ity), self-regulatory processes or goals (intention, plan- dence for mediation, or 3) strong evidence for mediation. ning, goals, self-regulation, behavioural processes) and social expectancies (social support, subjective norm) Results were included. The literature search yielded a total of 6620 potentially Study quality was assessed using the checklist tool relevant records. Of these, 359 abstracts and full text developed specifically for mediator analyses by Lubans, Foster and Biddle [21] and three additional items (i.e., measure reliability, appropriate analysis methods, assess- PotentiallyrelevantcitationsidentifiedfromISI ment of change in mediator preceding change in the out- WebofKnowledge,MEDLINE,psychINFO,and come) from Cerin and colleagues [22]. The tool was SPORTDiscus(N=6608) created with similar scoring to the Cochrane Collabora- Citationsidentifiedthroughothersources (N=12) tion's instrument for assessing risk of bias [23] and Numberofduplicatescitations includes 11 questions answered with a yes (1) or no (0) removed(N=3970) format. High quality is considered with scores of nine to Potentiallyrelevantcitationsscreened 11, moderate quality was considered with scores of five to (N=2650) eight and low quality was considered with scores of zero Citationsexcluded(N=2291) to four. Following the suggestions of the Grade Working Reasons:irrelevanttoreview (N=2291) Group [24], the overall quality of the studies was reported to describe the general state of research on the topic and Potentiallyappropriatecitationstobe includedinthereview(N=359) this included low quality studies. This was followed by Citationsexcludedfromthereview (N=330) analyses of the high and moderate quality studies, how- Reasons:nonexperimental/weak ever, in order to make judgements with some protection design(N=117);PAchangenot from risk of bias [21,23]. reported(N=41);mediatorvariables notexamined(N=76);dissertations, Studies were coded by whether the intervention was thesis,andabstracts(N=33);clinical population(N=26);noresults effective in changing behaviour and subsequently with an reported(N=18);other(N=19) approach used by Cerin and colleagues [22] that outlines Studiesincludedinthereview(N=29) mediator models by tests of action theory, conceptual Uniquetrialsincludedinthereview(N=27) theory, and simultaneous test of both action and concep- tual theories (i.e., mediated effect). Specifically, the action Figure 1 Results of the Literature Search. Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 4 of 11 http://www.ijbnpa.org/content/7/1/37 Table 1: Characteristics of Included Trial Reports (N = 27) Table 1: Characteristics of Included Trial Reports (N = 27) Characteristic Value Follow up test post 8 (29) intervention, N (%) Study Design PA target, N (%) Trial, N (%) 30 minutes MVPA most 17 (62) Randomized Control 16 (59) days/week Trial 30 minutes MVPA 3 4 (14) 2 group experimental 1 (3) days/week Quasi-experimental 4 (14) 20 minutes VPA 3 days/ 2 (7) Stratified Control Trial 1 (3) week Non random assignment 1 (3) Pre post test 4 (14) Outcome measures Arm, N (%) 3 Arm trial 7 (25) PA, N (%) 2 Arm trial 16 (59) PAR 7 (25) 4+ Arm trial 3 (11) GLTEQ 6 (22) Sample size, median (min, 150 (44, 31,420) CHAMPS 2 (7) max), N IPAQ 3 (11) Quality score, median (min, 6 (3, 7) SQUASH 1 (3) max) Objective measure 2 (7) Other self-report 7 (25) Participant population questionnaire No. of psychological 3 (1, 6) All Female trial, N (%) 7 (25) assessment tools, median Both gender trial, N (%) 20 (74) (min, max) Setting, N (%) Practice 4 (14) Reporting outcomes Home 2 (7) Work Site 3 (11) Change in PA behaviour, N 27 (100) (%) WIC 1 (3) Change in mediators, N (%) 27 (100) University 3 (11) Mediator analysis, N (%) 6 (22) Community 3 (11) Not reported 11 (40) Type of mediation test (N = 6) Intervention Baron and Kenny, N (%) 3 (50) Unspecified, N (%) 2 (33) Theory, N (%) Mackinnon et al., N (%) 2 (33) SCT 3 (11) Freedman-Schatzkin, N (%) 1 (16) TTM 9 (33) Bootstrap, N (%) 1 (16) PMT 2 (7) *note: some studies employed more than one type of test SDT 2 (7) TPB 3 (11) reports were obtained and reviewed. Twenty nine studies Duration, median (min, max), 12 (2, 104) describing 27 unique trials passed the eligibility criteria wk and were therefore included [25-52] (see Figure 1 based on QUOROM/PRISM guidelines [53]). These 27 trials were not included in the prior reviews on this topic [3,9]. Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 5 of 11 http://www.ijbnpa.org/content/7/1/37 Study characteristics the 11 samples demonstrating evidence that the interven- The 27 trials examined different types of interventions on tion had an action theory link. Of the remaining 11 sam- physical activity behaviour (see Tables 1 and Additional ples where the intervention demonstrated change in PA file 3). In terms of quality rating, five trials were identified [27,29-31,37,38,44,46-48,52], all showed evidence of an as low quality [33,39,42,45,54] and were not subsequently action test link, whereby at least some of the proposed included in the analyses (see Additional file 5). Of the mediating constructs changed from the intervention. remaining 22 trials, one was scored as high quality [44] These were not distinguishable by methodological char- and all others were deemed of moderate quality. Most acteristics. For example, studies ranged from college studies used constructs from a chosen theory with inten- undergraduates [46,48] to the general population [29,47] tions of increasing the participants' PA behaviour. The or specified populations [30,31]. Proposed mediators design of the interventions were either randomized con- included constructs from TTM [47], SCT [30], PMT [46], trol (N = 16), two group experimental (N = 1), quasi SDT [35], and TPB[48] and duration of the intervention experimental (N = 4), stratified control trial (N = 1), non ranged from two weeks [46] to one year [37]. Further, the random assignment (N = 1), or pre-post test (N = 4). Tri- interventions for these studies ranged from relatively als ranged from two to eight arms, with the majority straightforward messaging [46,48] to more intensive and using a two or three arm design comparing a high theo- long term counselling and workshops [30,31], while par- retical fidelity intervention to a standard public health ticipants ranged from carefully screened inactive samples intervention group (N = 20). Six other two arm studies [47] to no consideration of baseline physical activity [46] compared a high fidelity intervention to a control group. and comparisons were with true controls [48] or generic The settings of the studies included universities (N = 3), physical activity intervention groups [47]. general practice (N = 4), worksites (N = 3), and commu- Of these 11 studies to show evidence that the interven- nity settings (N = 3). Sample size ranged from 44 to tion could change PA and support the action test link, 31,420. Participants were of both genders (N = 20), or only five reported a conceptual theory test women only (N = 7). Physical activity was most com- [27,29,44,47,52], and six reported a mediator test monly assessed using IPAQ (N = 3), 7 day PAR (N = 8), [27,29,37,44,47,52]. All five conceptual theory tests and GLTEQ (N = 6). The interventions were based on showed at least some support for a link between a pro- SCT (N = 3), TTM (N = 9), TPB (N = 3), SDT (N = 2), and posed mediating construct and PA change, but the result- PMT (N = 2) among others. The interventions ranged in ing tests of mediation was supported in four [27,29,37,47] length from two weeks to 24 months. Nine studies had of the six samples. follow up tests from one month to one year after the end Evidence of Mediation by Theory of the intervention. The follow up tests ranged from short Transtheoretical Model interventions with long follow up periods (N = 2) to fol- Eight of the 22 samples employed constructs of the TTM low up tests with a length approximately equal to the as mediators of change (defined as including at least two length of the intervention period (N = 7); for example a 6 TTM constructs specified by Prochaska and DiClemente month intervention with a 6 month follow up. Interven- [55]) [28,31,32,34,36,44,47,56]. In all cases the studies tions examined the effects of counselling or group ses- were well-controlled designs where the TTM concepts sions (N = 11), telephone (N = 2) or email reminders (N = were employed in the interventions. One study, however, 5), print materials (N = 4), a combination (N = 4), and did not employ these interventions to standard control or other methods on PA levels and mediating variables. exercise prescription [36] and should be noted as deviant Most studies had a physical activity target set at 30 min- from the other eight studies. Furthermore, four of these utes of moderate intensity activity most days of the week eight studies reported a null effect of the intervention on (N = 15). Six studies set a target of three days of activity, PA change [28,32,36,49] and subsequent null action the- either vigorous (N = 2) or moderate (N = 4), while two ory tests on TTM constructs. The remaining four studies studies opted for a target of either 20 minutes of vigorous [31,44,47,52], however, all had evidence of at least one activity for three days per week, or 30 minutes of moder- TTM construct showing an action theory link. Three of ate activity for five days a week. these studies tested for a conceptual theory link with sig- General Evidence of Mediation nificant evidence for at least one TTM construct and Of the 22 samples, 11 did not show evidence that the these three studies also employed mediation effect tests intervention was effective in changing PA [44,47,52]. Interestingly, two of these studies demon- [25,26,28,32,36,40,41,43,49-51], thus failing the first con- strated that TTM mediators failed to attenuate the rela- sideration in most investigations/analyses of mediators tionship between the intervention and behaviour [44,52]. [11]. These studies generally had null results on the pro- By contrast, Napolitano et al. [47] demonstrated that posed mediators as well with only four [25,26,41,51] of behavioural processes of change (and cognitive processes Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 6 of 11 http://www.ijbnpa.org/content/7/1/37 as a suppressor) were able to account for the relationship constructs in a sample of undergraduate students between the intervention and behaviour in a formal although no formal conceptual theory test and mediation mediation test. Taken together, the TTM currently has analyses were conducted. Obviously the limited applica- mixed results in terms of intervention efficacy and in tions of PMT warrant more research. tests of mediation of its constructs. Self-Determination Theory Social Cognitive Theory Two studies have employed SDT (defined as including at Three studies have tested SCT (defined as including at least two constructs as specified by Deci and Ryan [14]) least two constructs as specified by Bandura [57]) in interventions using randomized experimental designs [30,37,51]. Two of the studies followed controlled trials in community samples [35,43]. Both studies employed [30,51], while the other employed a quasi-experimental interventions tailored to the concepts of SDT. Levy and design [37]. Furthermore, one [51] of these three studies Cardinal [43] employed a print mail-out intervention and did not support the effect of the intervention on behav- did not show changes in SDT constructs or behaviour, iour although all studies did have some support for an thus failing to support the action theory test and the link action theory link. None of the studies tested for a con- of the intervention to PA. By contrast, Fortier et al. [35], ceptual theory link, but Hallam and Petosa [37] provided used a primary care intervention setting and showed the evidence that self-regulation was a mediator of behaviour intervention had an effect on behaviour and an action at 12 months post-intervention, but did not show support theory link for SDT constructs of autonomy (motivation for self-efficacy or outcome expectations. It should be and support) but not competence. The investigators also noted that this mediation relationship was also inconsis- reported support for a conceptual theory link between tent and not present at six weeks or six month assess- autonomy support and PA but no formal tests of the ments and it did not examine mediation using product-of mediation effect was implemented. More research is coefficient tests recommended by MacKinnon and col- needed to evaluate SDT as a mediator of behaviour given leagues [10]. Thus, there is evidence for possible media- these limited findings. tion between selected SCT constructs and intervention- Evidence of Mediation by Construct PA change but the available studies are extremely limited Self-Efficacy/Perceived Control and mixed at present. Nineteen of the 22 studies employed a self-efficacy type Theory of Planned Behaviour construct, defined as an appraisal of confidence or capa- Three studies have employed the TPB (defined as includ- bility to perform physical activity. Of these, nine had null ing at least two constructs as specified by Ajzen [18]) effects of the intervention on PA change [40,48,50]. The methods for these studies include two [25,26,28,32,36,40,49-51] and only two of these showed experimental persuasive communication interventions support for subsequent action theory tests [25,26]. among undergraduates [40,48] and one quasi-experimen- Among the remaining 10 studies to support the initial tal community design [50]. Two of these studies, however, intervention-PA link, seven supported a significant show null results in terms of a link between the interven- action theory test for the effect of the intervention on tion and PA as well as the action theory test for a link changes in self-efficacy/control [27,30,38,46-48,52]. Four between the intervention and TPB constructs [40,50]. of these seven also reported conceptual model tests The single study [48] to show support for an effect of the [27,44,47,52] and three supported a link between changes intervention on changes in PA demonstrated action the- in self-efficacy/control and changes in PA [27,44,52]. Of ory links with intention, perceived behavioural control, the five studies that employed a formal mediation analysis and affective attitude (dependent on baseline values) yet [27,37,44,47,52], however, only one showed significant no conceptual theory test formal mediation analysis was support for self-efficacy [27]. In this case, Blanchard et al. performed. Overall, the evidence is too limited from a [27] demonstrated that task self-efficacy (efficacy to paucity of research and lack of actual behaviour change in physically perform the behaviour) was a significant medi- the interventions to make a judgement of the effective- ator of behaviour change but barrier self-efficacy (confi- ness of TPB as a mediator in PA interventions. dence to overcome hassles) was not. Thus, self-efficacy Protection Motivation Theory has considerably limited support for its role as a mediator Two studies have applied PMT (defined as including at of PA changes due to interventions at present. least two constructs as specified by Rogers [19]) [46,56]. Outcome Expectations Plotnikoff et al. [56], were unable to show effects of their Fourteen of the 22 studies reviewed included outcome work site intervention on the proposed mediators or expectations, defined broadly as expected/anticipated behaviour, thus failing to support the action theory test consequences from behavioural or lack of behavioural and the intervention-PA link. Milne et al. [46] showed engagement, as potential mediating constructs that their intervention had an effect on short-term PA [28,30,32,36,37,40,44,46-52]. Of these, seven showed null change and supported the action theory link for all PMT Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 7 of 11 http://www.ijbnpa.org/content/7/1/37 effects for the intervention on PA [28,32,36,40,49-51] and Social Constructs all but one of these [51] also reported non-significant Variables with social referents typically encompassed effects for the action theory test. Of the remaining seven either subjective norm (perceived pressure to perform studies, all but one [44] showed support for the action the behaviour) or social support (support from others to theory test of the intervention's effectiveness in changing perform the behaviour). Nine studies employed such outcome expectations. It is interesting to note that many variables in these studies [29,34,35,39,40,43,48,50,51] but of these studies measured and targeted outcome expecta- five of these studies did not show support for the effec- tions underlying the affective domain in the intervention tiveness of the intervention on changes in PA [40,43,49- (i.e., enjoyment, pain, fear) as opposed to more instru- 51] nor did they demonstrate significant action theory mental and distal outcome expectations (i.e., weight loss, tests on the social constructs. Three of the remaining fitness, chronic disease). Indeed, Parrott et al. [48] four studies showed significant action and conceptual showed a significant action theory test with affective out- theory tests and it is notable that all three studies contain come expectations but a non-significant action theory support rather than normative constructs [29,35,52]. test with instrumental outcome expectations when mea- Tests of the mediated effect, however, were conducted sured separately. Only three studies, however, reported among two of these studies and the results were mixed. subsequent conceptual theory tests [44,47,52], and the Specifically, Cerin and colleagues [29] demonstrated four tests to examine the mediation effect all reported mediation while Fahrenwald et al. [34] did not show evi- non-significant findings for outcome expectation con- dence for the mediation capacity of social support. Thus, structs [37,44,47,52]. Overall, there is limited evidence social constructs have some evidence for mediation of PA for outcome expectations as a mediator of PA interven- interventions and behaviour but results are limited and tions. Distinctions by affective/proximal and instrumen- positive findings have only been with support, not norms. tal/distal expectations in action theory tests suggest there may be more evidence for the affective/proximal domain Discussion in mediation but these studies did not report conceptual Theories of PA behaviour suggest that particular con- theory tests or specific mediated effects. structs are critical antecedents of behavioural engage- Self-Regulatory Processes ment. These constructs are hypothesized as components Defined generally as planning, scheduling, and self-orga- of a causal chain, suggesting that if the mediators are nizational behaviours, self-regulatory processes were changed, behaviour change should follow [6]. Early measured in some capacity in 16 of the 22 studies reviews based on theoretical mediators of behaviour [28,31,32,34,36-38,40,41,44,46-48,50,51,58]. Eight of change, however, suggested that few formal tests of medi- these studies showed null effects for the intervention on ation had been conducted and limited evidence was avail- behaviour change [28,32,36,40,41,49-51] and only two of able to support this proposition [3,9]. Therefore, the these had significant action theory tests [41,51] sugges- purpose of this review was to provide an update of the lit- tive of generally null/ineffective trials. Of the remaining erature on PA interventions that have included proposed eight studies, however, six reported evidence of signifi- mediators of behaviour, focusing specifically on primary cant action theory tests [37,44,46-48,52]. For example, prevention in adults since the time of these prior reviews. Milne et al. [46] showed that planning/implementation The review yielded 29 studies from 27 independent intentions affected increases in behaviour beyond those samples to appraise our current understanding of PA of an intervention that increased self-efficacy and out- mediators in interventions. Five studies were omitted come expectations. Despite these supportive action the- from the analyses due to low quality but the other 22 tri- ory tests, only three studies reported conceptual theory als showed moderate (n = 21) or high (n = 1) quality and tests, although all provided support for self-regulatory thus relatively low risk of bias. Almost all studies did not constructs [44,47,52]. Finally, of the four tests to examine meet the category for high quality because they failed to a mediated effect, Hallam and Petosa [37] and Napolitano include a direct measure of physical activity behaviour et al. [47], showed that changes in self-regulation (via self- and did not report on a pilot intervention to demonstrate regulation and behavioural processes of change respec- that it could affect the mediators. Otherwise, the 22 trials tively) mediated the relationship between the interven- generally showed many high quality features such as ran- tion and changes in PA. Still, there were two studies that dom assignment, a theoretical-base, reliable and valid demonstrated no mediation of a successful intervention measures of the mediators, and reliable measures of self- through self-regulation processes (behavioural processes) reported PA. [34,44]. Overall, there is some evidence for mediation Overall, 11 studies showed that the intervention had an between self-regulation processes and behaviour but effect on PA behaviour change and all of these studies results are mixed. subsequently had an action theory link [59]. That is, all 11 Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 8 of 11 http://www.ijbnpa.org/content/7/1/37 studies showed some evidence that the intervention also in PA; however, three of these four studies showed an changed the proposed mediators. By contrast, a concep- action theory link. Social support was also a mediator of tual theory link [59] was seldom reported (5/11 studies). behaviour change in one formal test of mediation, but Conceptual theory links demonstrate that changes in the was unable to show a mediated effect in the only other mediators are related to the PA outcome. These are often test with this construct. There was no evidence for the the foundation for using a theory or mediator construct mediation capacity of subjective norm. Although limited before initiation of the intervention [11], but future work literature precludes any definitive conclusions, social needs to test this link regularly in reported trials with constructs, particularly social support, may have utility as mediators. Formal tests of mediation were also only con- mediators of change but findings are mixed at present. ducted in six of the 11 cases where the procedure may A key finding of the review, however, was that half the have been appropriate (i.e., intervention effect on behav- interventions failed to change both behaviour and the iour, evidence of action theory link, conceptual theory proposed mediators through the action theory link. This link or probable conceptual theory link). In terms of does not challenge the internal structure of our leading behavioural mediation by theory, TTM, SCT, TPB, PMT, theories and constructs at present as much as demon- and SDT all showed some evidence for action theory tests strate that our interventions are generally ineffective. To and all have shown evidence for conceptual theory tests evaluate the mediation capacity of a theory, the behav- in the past, but only the TTM employed tests of a medi- ioural link and action link are important first steps in ated effect of its constructs. The results, when divided by mediation [11]. Pilot studies showing evidence that the theory, are too limited in number to make particular intervention can change the proposed mediators are rec- judgements at present. ommended in future research before large-scale trials are A division at the construct level [6,12,18,20], however, conducted. provides a larger sample for assessment. Self-regulation The poor performance of PA interventions has been constructs (e.g., planning, behavioural processes) from duly recognized [3,4], and it is much easier to comment trials where the intervention changed PA behaviour on this problem than to provide solutions. Nevertheless, showed 75% (6 of 8 studies) support for action theory it is important to provide some commentary on this issue. tests and all three of the conceptual theory tests con- A most pragmatic possibility for these results may be ducted were significant. Mediated effect tests of the con- attenuation from measurement error. For example, indi- struct, however, were mixed with two showing support rect (self-report) PA measures featured in these studies and two not providing evidence for mediation. Our may lack the sensitivity to distinguish change between the appraisal of self-regulation is similar to the original com- groups and the psychological constructs may equally lack ments made by Lewis et al. [9]; the construct has the most precision [3]. Direct measures of PA are recommended in support thus far but still demonstrates mixed findings. future trials. Still, this seems unlikely to be the sole reason Still, it seems prudent to include a self-management and for these null effects; many of the studies were able to self-regulatory component to PA interventions. demonstrate time effects (i.e., main effects), and the pro- Results of self-efficacy and outcome expectation-type posed mediators generally show moderate to large bivari- constructs as mediators were weak or limited. Self-effi- ate correlations with PA in prediction tests [e.g., [61]]. cacy constructs among intervention studies that affected Clearly more innovation and higher fidelity interven- PA change showed relatively strong evidence for action tions are needed. In the studies reviewed, there was a very theory (7 of 10 studies) and conceptual theory (3 of 4 similar genre of intervention. These typically focused on studies reported) links, but a mediated effect was not a persuasive educational component about the benefits of supported in four of the five formal tests conducted. Out- PA and hazards of inactivity followed by problem solving come expectation constructs had similar results in terms suggestions to regulate action and overcome barriers. of evidence for an action theory link (6/7 studies) but Although this approach could be helpful to some, it was zero of the four tests for a mediated effect were signifi- not helpful to change proposed mediators in over 50% of cant. There was some notable differences between affec- the cases reviewed and these null results were not readily tive and instrumental outcome expectations (see [60] for identifiable as discrepant intervention styles from suc- extended commentary) with positive changes in affective cessful trials. The problem occurring may be that the outcome expectations linked to positive changes in approach is an insufficient band-aid to overcome the real- behaviour more than instrumental outcome expectations. world obstacles and different values that some inactive Still, the relatively few studies on this topic and absence of participants experience. Social and environmental struc- any formal mediation tests render this point as specula- tures may be so grounded and geared to sedentary life- tive at present. styles that individual-level, inexpensive, patches may not Social constructs were limited to only four studies resonate with the inactive populace [41]. The limits of where the intervention had produced significant changes these "downstream" approaches have been recognized Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 9 of 11 http://www.ijbnpa.org/content/7/1/37 [62]. Approaches at system-level social and environmen- mediation. The general null findings of many behavioural tal change may be needed to aid many people [63]. This interventions are a timely concern. Innovation and approach, of course, is costly and does not lend itself to increased fidelity of interventions is needed and should the tight-budget three-year RCT; indeed, it is likely to be a priority for future research. conflict with other societal and industrial aims. Interacting with these more systemic social and envi- Additional material ronmental issues may be systemic internal issues. Enact- Additional file 1 Excluded articles. This file contains the list of articles ing a potentially fatiguing, boring, and time-consuming that did not meet our inclusion criteria. The articles are grouped based on behaviour on a repeated basis in the face of other behav- the criteria the articles failed to meet. ioural options and values is likely to pose an enormous Additional file 2 Search syntax. This file contains the search terms used daily challenge to many people. Some of this may arise in this review. Additional file 3 Review Table of proposed mediators and physical from differences in genetic predisposition and other indi- activity behavior. This file contains data extracted from each included arti- vidual differences that are not easily intervened upon cle in table form for quick reference. [64], while some of these decisions may be the result of Additional file 4 Data extraction. This file contains the data extracted informed free will. from each included article. Additional file 5 Quality of studies using tool developed by Lubans, When considering these possibilities, it seems impor- Foster, and Biddle (2008). This file contains the tool used to assess the tant for future interventions to become more innovative quality of each study included in the review. Each study was assessed by a and target proposed mediators with a higher fidelity. series of questions listed below. BMI: Body Mass Index; RCT: Randomized control trial; PA: physical activity; MI: motivational interviewing; ES: effect Using the tenets of SCT as a guide[57], the experiential size; OR: odds ratio; PAR: physical activity recall. T TM: transtheoretical model; qualities of the behaviour seem the most telling way to POC: processes of change; SCT: social cognitive theory; IPAQ: International affect cognitions rather than passive approaches. Experi- Physical Activity Questionnaire; GLTEQ: Godin Leisure Time Exercise Ques- tionnaire; SDT: self-determination theory; PMT: protection motivation the- ences of valued personal outcomes (e.g., enjoyment, plea- ory; TPB: theory of planned behaviour; PCB: perceived behavioural control; sure, satisfaction) and behavioural control/self-efficacy, CHD: coronary heart disease. through shifts in behavioural, environmental and social experiences of PA may be the most effective intervention Abbreviations SD: Standard Deviation; IPAQ: International Physical Activity Questionnaire; 7 alongside increasing self-regulatory skills. At this time, day PAR: 7 day Physical Activity Recall; GLTEQ: Godin Leisure Time Exercise we recommend that interventions focus on altering the Questionnaire; RCT: Randomized Control Trial; ES: Effect Size. behavioural experience in an attempt to improve fidelity Competing interests and affect change in proposed mediators. The authors declare that they have no competing interests. It is important to highlight the limitations of this review in order to provide a context for the results. First, the Authors' contributions RR conceived the review, participated in the coordination of the search, assessment is limited to published work and may be sub- assessed study quality, analyzed and interpreted the results, and drafted the ject to publication bias. Given the high rate of null effects majority of the manuscript. LP carried out the literature search, participated in in these results, the bias may be minimal but no formal the study quality assessment, compiled the results into tables, and drafted the methods section. Both authors read and approved the final manuscript. test of publication bias can be conducted. Second, the work contained in this review is limited to English writ- Authors' information ten journals and thus the results cannot generalize to RR, PhD, holds a Canadian Institutes for Health Research New Investigator Award and is currently an Associate Professor in the School of Exercise Science, studies conducted and published in other languages. Physical and Health Education at the University of Victoria. Finally, the review is limited to the search terms and data- LP, BPE/BEd, MA, is a Research Associate in the Behavioural Medicine Labora- bases contained in our methods section, which followed tory at the University of Victoria. the precedent of Baranowski et al. [3] and Lewis et al. [9]. Acknowledgements Studies that have not been abstracted with these key Production of this paper has been made possible through a financial contribu- words will be missing from our review. tion from the Public Health Agency of Canada. The views expressed herein do not necessarily represent the views of the Public Health Agency of Canada. We also acknowledge the helpful comments from Andrea Tricco and Michelle Kho. Conclusions In summary, less than half of the 22 studies reviewed Author Details showed evidence that the intervention changed PA and 1 Behavioural Medicine Laboratory, Faculty of Education, University of Victoria, Victoria, BC, Canada and School of Exercise Science, Physical and Health the proposed meditating constructs of behaviour. Among Education, University of Victoria, Victoria, BC, Canada the studies to show these effects, about half subsequently performed tests of the mediating effect or that changes in Received: 21 July 2009 Accepted: 11 May 2010 Published: 11 May 2010 the proposed mediator were linked to changes in PA. T © T In h h t2 i i e s s 0 rn arti i1 sa 0 an t R io cle h O na o i p d s l J e ava es n o a A ur n icce lable na d Pf l o ss arti a f f B e ro ff em ha lcl i; l :e h v ic d io ttp:/ ei rn s a t s lri ee N /bu w u B w tte riit o w d iM o .i u jbn n ed C n a d n p e d a e r th P .n ot h rre g ys a te / lic Lt co rm an d. l A ts e c o n tif t/ v th i7/ tye 1/ 2010, C 37 reati 7 ve :37 Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tests of mediated effect also showed mixed outcomes. Differences by theory were not discernable at this time, but self-regulation constructs had the most evidence for Rhodes and Pfaeffli International Journal of Behavioral Nutrition and Physical Activity 2010, 7:37 Page 10 of 11 http://www.ijbnpa.org/content/7/1/37 References 27. Blanchard CM, Fortier M, Sweet S, O'Sullivan T, Hogg W, Reid RD, Sigal RJ: 1. 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Rhodes RE: The built-in environment: The role of personality with physical activity. Exercise and Sport Sciences Reviews 2006, 34:83-88. doi: 10.1186/1479-5868-7-37 Cite this article as: Rhodes and Pfaeffli, Mediators of physical activity behav- iour change among adult non-clinical populations: a review update Interna- tional Journal of Behavioral Nutrition and Physical Activity 2010, 7:37

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