Intentions are defined as the instructions to oneself to perform a certain behaviour or to achieve a goal (Triandis, 1980). They reflect one’s motivation to act and are a direct precursor to behaviour (Ajzen, 1985). Intentions for physical activity have been shown to be a predictor of physical activity behaviour (Chatzisarantis & Hagger, 2005; Hagger, Chatzisarantis, & Biddle, 2002; Hagger, Chatzisarantis, & Harris, 2006; K. Hamilton & White, 2008; Rhodes, Blanchard, Matheson, & Coble, 2006; Rhodes & Courneya, 2003), while also being influenced by affective attitudes and perceived behavioural control (e.g. Armitage, 2005; Eves, Hoppéa, & McLaren, 2003) and social norms (Lowe, Eves, & Carroll, 2002), as well as self-efficacy (Hagger et al., 2002). Intentions have also been shown to be associated with self-determined motivation for physical activity whereby autonomous motivation positively predict exercise intention (Chatzisarantis & Hagger, 2009; Hagger et al., 2002; Ingledew et al., 2014), amount and satisfaction (Ingledew et al., 2014). Specifically intrinsic and identified regulation as well as amotivation positively predict intentions, while external regulation negatively predicts intentions (Lim & Wang, 2009). Change in controlled forms of motivation has been shown to be positively predictive of changes in attitude, self-efficacy and intentions, while change in intention predicted change in physical activity (Jacobs, Hagger, Streukens, De Bourdeaudhuij, & Claes, 2011).
Despite intentions being good predictors of behaviour (e.g. Sheeran, 2002), it has been suggested that strong goal intentions alone are not sufficient to engage in a behaviour (Gollwitzer, 1993; Gollwitzer & Brandstätter, 1997). Given the associations between intentions and behaviour, planning behaviour and implementation intentions (II) were suggested as mechanisms to fill this gap (Fleig et al., 2013; Gollwitzer, 1993; Reuter, Ziegelmann, Lippke, & Schwarzer, 2009) as demonstrated in the model of action phases (Gollwitzer, 1990; Heckhausen & Gollwitzer, 1987). Paralleled with Ajzen (1985) intention formation, a deliberative phase was proposed whereby the costs and benefits of the behaviour are considered, similarly to where behaviour is predicted by attitudes, subjective norms and
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perceived behavioural control in the theory of planned behaviour (Orbell, Hodgkins, & Sheeran, 1997). A post-decisional, implementation phase or intention realisation phase is also added (Gollwitzer, 1990; Heckhausen & Gollwitzer, 1987), involving efforts to promote initiation of the behaviour, through planning where and when to start.
Through implementation intentions, habit like behaviour can be formed (Fleig et al., 2013; Gollwitzer & Brandstätter, 1997), interventions have also been shown to be more effective if they aim to foster habits (e.g. in exercise; (Fleig, Lippke, Pomp, & Schwarzer, 2011). II also help aid the retrieval of intentions from one’s memory and reduce the capacity of one’s previous behaviour to predict future behaviour (Orbell et al., 1997). Forming implementation intentions has been shown to be effective in increasing the likelihood of behaviour (review: Gollwitzer & Sheeran, 2006), for example in epilepsy and stroke medication adherence (Kersten, McCambridge, Kayes, Theadom, & McPherson, 2015), quitting smoking (Armitage, 2007), healthy eating (Adriaanse, Vinkers, De Ridder, Hox, & De Wit, 2011), uptake of cancer screening (Orbell, Campbell, & Weller, 2016), reduction of alcohol consumption and binge drinking (Norman et al., 2016; Norman, Webb, & Millings, 2019), multimedia learning (Stalbovs, Scheiter, & Gerjets, 2015), reducing speeding behaviour (S. E. Brewster, Elliott, & Kelly, 2015), reducing red meat consumption (Rees et al., 2018), improving sleep and sleep hygiene (Mairs & Mullan, 2015), blood donation behaviour (Wevers, Wigboldus, van den Hurk, van Baaren, & Veldhuizen, 2015) and reducing escape- avoidance behaviour in relation to pain (Karsdorp, Geenen, Kroese, & Vlaeyen, 2016). In relation to physical activity behaviour, II have also been shown to increase physical activity behaviour and self-regulation (Epton & Armitage, 2017), increased step count (Arbour & Martin Ginis, 2009; Liau, Neihart, Teo, Goh, & Chew, 2018; Stephanie A. Robinson, Bisson, Hughes, Ebert, & Lachman, 2019; W. M. Rodgers et al., 2014), stair use (Kwak, Kremers, van Baak, & Brug, 2007), goal progress (Carraro & Gaudreau, 2011), higher scheduling self- efficacy, overcoming of barriers to walking and greater perceived behavioural control (Arbour & Martin Ginis, 2009), improved exercise self-efficacy and exercise behaviour in high school students (Wang, Xu, Yu, & Zhou, 2019), moderate-vigorous physical activity (MVPA; Andersson & Moss, 2011; Armitage & Arden, 2010; Marquardt, Oettingen, Gollwitzer, Sheeran, & Liepert, 2017; McGowan, North, & Courneya, 2013), time-relevant exercise self- efficacy (Stephanie A. Robinson et al., 2019), exercise enjoyment (Ivanova, Yaakoba-Zohar,
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Jensen, Cassoff, & Knäuper, 2016) and adherence to physical activity and scheduling self- efficacy (Murray, Rodgers, & Fraser, 2009). Roberts, Maddison, Magnusson, and Prapavessis (2010) showed that II and goal intentions acted as mediators between attitudes, subjective norms (full mediator), task and barrier self-efficacy and perceived behavioural control (partial mediator) and behaviour. Blanchard (2008) demonstrated how II acted as a complete mediator between intentions and behaviour at 3 and 6 months while intentions were predicted by attitudes, subjective norms and perceived behavioural control. They have also been shown to be effective in improving physical activity in specific groups such as young children (Armitage & Sprigg, 2010), pregnant women (Gaston & Prapavessis, 2014) and those with spinal cord injuries (Latimer, Ginis, & Arbour, 2006), as well as those in orthopaedic rehabilitation (Ziegelmann, Luszczynska, Lippke, & Schwarzer, 2007), pulmonary rehabilitation and Myocardial Infarction patients (Luszczynska, 2006) and in older people (Wolff, Warner, Ziegelmann, Wurm, & Kliegel, 2016).
However, they are not always consistent, with a number of studies finding no effect or a negative effect of planning or II formation on physical activity behaviour (Budden & Sagarin, 2007; Carrera, Royer, Stehr, Sydnor, & Taubinsky, 2018; Gerber, Mallett, & Pühse, 2011). Some explanation for this might come from studies that have found those interventions only effective in those with strong self-efficacy beliefs (Luszczynska & Haynes, 2009), in those with unstable intentions (Godin et al., 2010), in those who plan based on specific occasion cues and highly instrumental plans and those who plan less specific behavioural responses (Fleig et al., 2017), in those with high intentions (De Vet, Oenema, Sheeran, & Brug, 2009; Scholz, Schüz, Ziegelmann, Lippke, & Schwarzer, 2008) and in those high in self-efficacy (Luszczynska, Schwarzer, Lippke, & Mazurkiewicz, 2011). In addition, intentions, motivation, plan reminders, goal types, planning types, perfectionism, procrastination and stress have all been shown to be moderators of the relationship between II and behaviour (Prestwich & Kellar, 2014). Plan reminders (Prestwich, Perugini, & Hurling, 2009, 2010; M. A. V. da Silva, São- João, Brizon, Franco, & Mialhe, 2018) and the specificity or quality of II (De Vet et al., 2009; Ziegelmann, Lippke, & Schwarzer, 2006) have been shown to be especially important in their effectiveness.
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Self-determined motivation has also been shown to predict planning which in turn predicts exercise frequency (Lutz, Karoly, & Okun, 2008). Identified regulation has also been shown to be associated with the formation of spontaneous II for exercise as well as there being an indirect effect of identified regulation on exercise behaviour via spontaneous II (Brickell & Chatzisarantis, 2007). Research has also suggested that motivation might be more important in predicting physical activity than planning (Rhodes et al., 2006). Pride has also been shown to be predictive of intentions for physical activity (Gilchrist & Sabiston, 2018), while self- compassion has also been shown to predict health promoting behavioural intentions (Sirois, 2015).