Combining motivational and volitional interventions to promote physical activity and fruit & vegetable intake
: a single blind randomised controlled trial with Spanish university students

Student thesis: Doctoral ThesisDoctor of Philosophy


Background: Despite physical activity and fruit & vegetable consumption’s substantial health benefits for reduction of disease risk and physical and psychological health (World Health Organisation, 2010), many young adults failed to achieve the recommended levels of these health-related behaviours (Martínez-González, 2011). 
Design: A single blind randomised controlled trial. 
Methods: The design, implementation and evaluation of an intervention to increase physical activity and fruit & vegetables consumption in Spanish undergraduates are reported in this thesis. In turn, the intervention comprised a motivational intervention guided by the Theory of Planned Behaviour (Ajzen, 1991; Fishbein & Ajzen, 2010) and a volitional intervention based upon the implementation of the intentions (Golwitzer, 1993). The motivational intervention was designed on the basis of a preliminary work which identified salient beliefs that should be targeted in intervention materials. 
Results: Analyses mainly showed that the intervention did not lead to significant change on physical activity and fruit & vegetable intake relative to the control condition. Despite the large battery of studies together with the present study, showing the success of the Theory of Planned Behaviour as a good model for the prediction of health-related behaviours, findings reported that the theory could not be meaningful applied to the modelling of change physical activity and fruit & vegetable in this population, even when supplemented with the implementation of the intention strategy. 
Conclusion: This result contribute to the growing body of research suggesting that theories that can be reliably applied to the prediction of intention or behaviour are not necessarily suitable to behaviour change (Hardeman et al., 2011). Researchers who wish to use the Theory of Planned Behaviour and the implementation intention strategy should consider the implications of this investigation for intervention design and behaviour change theory.
Date of Award1 Oct 2014
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorIan Norman (Supervisor) & Joanne Fitzpatrick (Supervisor)

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