Amongst the plethora of behaviour change theories an uneven frequency of theory use exists. Early social cognition models dominate the literature \citep*{Davis_2014}; models which collectively take a continuum approach to behaviour change and examine the predictors and precursors of health behaviours  \citep*{Bandura_2004}. Table 2 provides an overview of the most prevailing models utilised to explain health behaviours in a variety of populations (for an extensive review of behaviour change theories, see \citealp{Davis_2014}). Many theories of behaviour change draw upon similar, overlapping constructs  \citep*{Bandura_2004}. In fact, a theory guided thematic analysis review of 100 behaviour change theories identified five overarching, interconnected themes central to behaviour maintenance \citep*{Kwasnicka_2016}. Themes reflected the differential nature and role of motives, self-regulation, habits, psychological and physical resources, and environmental and social influences from initiation to maintenance. These themes were cross-validated by ten psychologists; with a high level of agreement (Krippendorff’s a = 0.87) upon individual assessment. Explanations to the centrality of these themes is summarised as follows.
Theoretical explanations largely propose that behaviour change depends on individual characteristics. For instance, sustained change is more likely to be achieved if a person has at least one maintenance motive that drives volitional behaviour and emphasises immediate and affective outcomes. That is, research consistently indicates that behaviour is likely to be repeated if it is congruent with a person’s identity, beliefs and values, if it is immediately pleasurable, and if the person is satisfied with the behavioural outcome REFERENCE. These intrinsic forms of motivation are hypothesised to have a stronger influence on behaviour maintenance than extrinsic motivation (which may comprise, for example, a desire ‘to avoid negative health consequences’) when maintained effort is required. As motivation levels regress and behaviour change becomes more costly, successful self-regulation is required to ensure that the behaviour is maintained. Self-regulation is based on a system of hierarchical goals and comprises an ongoing process of self-monitoring, self-evaluation and self-reinforcement \citep*{Kanfer_1972}. Changing one’s behaviour is an effortful process and an individual must be equipped with the psychological resources  necessary to overcome barriers; particularly to cope with stress, emotions, exhaustion and the temptation to revert to an ‘easier’ automatic prior behaviour. Coping efforts however place increasing demands on the self-regulatory system and drains mental resources; paving the way for behaviour lapse. In contrast to the conscious, reflective decisions made during self-regulatory processes, behaviours governed by automatic processes \citep{Kwasnicka_2016} are implicit and effortless, triggered by situational cues and formed through repetition of a behaviour within a specific context \citep{Lally_2009,Lally_2013} . Whilst largely unconscious \citep{bargh1992,Hofmann_2008}, habits often coincide with goals \citep*{Wood_2016}  and are largely dependent upon behaviour pleasure and intrinsic motivation motivation \citep*{Judah2018}; mediated by neural circuits that link cortical brain areas and the basal ganglia \citep{Yin_2006,Wood_2016}. With repeated performance of a new desired behaviour, the need for conscious self-regulation decreases and behaviour becomes habitual   \citep*{Wood_2016}, facilitating  behaviour maintenance  \citep{Kwasnicka_2016}. Thus, habit development should be facilitated by making desirable health behaviours salient and by cueing individuals towards healthy behaviours. Promisingly, interventions built upon healthy habit formation have yielded promising results for weight loss \citep{Carels2014,Lally_2007}, healthy eating \citep*{Gardner_2014} physical activity activity \citep*{Rhodes2010} and medication adherence \citep*{Bolman2011}. However, strategies which target habits should first focus on disrupting cue's to ameliroate residual undesirable behaviours \citep*{Verplanken_2008} as established memory traces are difficult to substitute in isolation \citep*{Bouton_2014}
 
 
Lastly, \citealp{Kwasnicka_2016} highlight the importance of community and environmental contributions to behaviour maintenance. Particularly, a supportive environment, positive social influences and constructive social change facilitate behaviour change maintenance (whether behaviour occurs under conscious or reflective processes), as these constructs lower the opportunity cost of new behaviours  \citep{Kwasnicka_2016} . In relation to the environmental context, for example, it is often the default to respond to the behavioural option most facilitated by the environment; particularly when active self-regulation becomes effortful and depletes resources. Thus, environmental factors determine the amount of active self-regulation and resource required in that if the environment is supportive of the newly adopted behaviour, it is easier to endorse. Social and environmental restructuring, for instance, is an effective route to reducing sedentary behaviours \citep*{Gardner_2015}. To this end, subtle environmental modifications may operate to alter health behaviours at the community level, providing 'nudges' in a desired direction and guiding individuals to certain choices without the use of conscious decision making \citep{Gill_2012,Marteau2012,Strack_2015}. This offers an effective and feasible route to altering health behaviours within large populations and are strategically targeted towards poor dietary habits and physical activity levels in low socio-economic areas \citep{Lakerveld2018}. Meta-analysis results indicate that dietary nudge interventions are relatively successful and can increase healthier consumption decisions by 15.3% on average \citep*{Arno2016}. Patently, concerns surround the use of this tactic relating to issues of empowerment and freedom \citep*{Blumenthal-Barby2012} freedom \citep*{Blumenthal-Barby2012} though such methods are generally well-accepted by the public \citep{Junghans2015,Petrescu2016}.
 
Thus far it is patent that accounts of behaviour change largely draw upon the centrality of individual characteristics to health behaviours. Self-efficacy is one factor which, although not presented in work by  \citet{Kwasnicka_2016}, surely merits acknowledgement for its powerful capacity to predict behavioural intentions above other factors \citep*{Maddux_1983} and contribute to behaviour maintenance \citep{Eccles_2012,Ashford_2010}.  Self-efficacy relates to a person’s beliefs about whether one can produce certain actions \citep*{bandura1997} and is a construct determined by one's performance accomplishments, their vicarious experience, external social persuasions, and physiological states  \citep*{Bandura_2004}. This core belief is a focal determinant in many behaviour change theories because it affects the processes of personal change both directly and by its capacity to mediate and moderate behaviours   \citep*{Bandura_2004}, further to influencing one’s goals and motivation to achieve   \citep*{bennet2016}, and their capacity to cope adaptively   \citep*{Rippetoe_1987} and persevere despite challenges. The construct plays a key role in several health behaviours related to chronic condition self-management, including medication adherence  \citep{Morrison_2015} and smoking, physical exercise, and dieting behaviours (Conner, 2005). For example, a systematic review of behaviour change aimed at reducing obesity reported that self-efficacy was amongst the mediators for longer-term weight control; in addition to  autonomous motivation self-regulation capabilities   \citep*{Teixeira_2015}. However, self-efficacy beliefs do not operate sufficiently in isolation to changing one's behaviours   \citep*{bennet2016}. Rather, its effects are moderated by outcome expectancies and the value placed on the behavioural goal \citep*{French2013}.
 
Whilst self-efficacy offers a buildable construct that can facilitate change, there is evidence to suggest that positive affect may offer a better predictor of long-term adherence to positive health behaviours. A meta-analysis of 82 studies indicates that positive affective attitudes are stronger predictors of engagement (relating to physical activity in this instance) than positive cognitive attitudes or levels of self-efficacy Rhodes, Fiala, & Conner, 2009); an effect sustained relatively long-term in even individuals previously naïve to such health behaviours (Williams et al., 2008Williams, Dunsiger, Jennings, & Marcus, 2012). Positive affect, in part, comprises a motive for enduring change (Kwasnicka, Dombrowski, White, and Sniehotta, 2016). Integrating evidence on positive affect with that on implicit process,  \citealp*{Van2018}     present the upward spiral theory of lifestyle change to address the mechanisms through which positive affect alters future health-related decision making. Here, positive affect experienced during health behaviours are considered to increase non-conscious motives for those health behaviours. This creates an implicit incentive salience and prompts everyday decisions to repeat desirable actions. In line with the broaden-and-build theory (Fredrickson), positive affect builds a suite of endogenous vantage resources over time, comprising biological resources (e.g., cardiac vagal tone) as well as cognitive (e.g., mindfulness), psychological (e.g., purpose in life), and social (e.g., positive relations with others) resources Fredrickson (2013). This further facilitates the positive affect experienced during positive health behaviours and strengthens non-conscious motives; predicting future engagement in health behaviours Rice & Fredrickson, 2017, and resulting in behavioural maintenance. Particularly, interventions aimed at increasing positive affect simultaneously facilitate the building of social connections. For instance, training in loving-kindness meditation   \citep{Kok_2010,Kok2015,Kok2013}  elicits positive emotion and this is moderated by baseline vagal tone. Increases in positive emotion lead to subsequent increases in vagal tone, mediated by an increase in the perception of social connectedness. Higher vagal tone predicts greater social engagement at follow-up, and higher social engagement in turn predicts further increases in vagal tone \citep*{Kok_2010}. This reflects a self-sustaining upward spiral between vagal function, emotion and social connections. 
 
The research conducted by highlights the important contributions of a variety of individual, community and environmental factors to the maintenance of positive health behaviours; with viable theoretical explanations to assist in the elucidation of potential mechanisms. However, models to date seldom address the needs and characteristics of individuals with chronic conditions and thus have minimal applicability regarding the context in which interventions for these populations are derived. In order to truly facilitate well-being, mechanisms proven to cultivate lasting positive change are pivotal \citep*{Rusk_2017}. To this end, \citet*{Rusk_2017}     present the theory of Synergistic Change to describe the pathways through which interventions (particularly relating to positive psychotherapy) cultivate lasting positive change in its recipients, and, subsequently, facilitate wellbeing.