Despite extensive efforts to promote active lifestyles, young people are becoming increasingly sedentary. One of the reasons for the failure of attempts to increase physical activity is the self-protective tendency to defend against messages that highlight personal failings. Research suggests that such resistance may be overcome by focusing attention on one's values and positive aspects of oneself - 'self-affirmation' (Steele, 1988). Self-affirmation has the potential to enhance the effectiveness of health promotion. At present, however, it is not clear how these potential benefits can be realised. Four experimental studies will examine how self-affirmation operates and with which message types it can most successfully combined (eg those emphasising the threat or ways to overcome it). These questionnaire-based studies will also show how self-affirmation interacts with other techniques designed to encourage enactment of health-promoting intentions (ie forming detailed plans). These objectives will be pursued by studying the promotion of increased physical activity amongst 16-24 year olds. Given that the majority of this age group are in education, employment or training, participants will be recruited from educational establishments that offer a valuable opportunity for physical activity interventions.

Older adolescents (N = 125) completed a self-affirmation or control writing task before reading about the health consequences of not meeting recommendations to be physically active for at least 60 min daily. Most of the sample did not achieve these levels of activity (98%, N = 123). Consequently, the message informed these participants that – unless they changed their behaviour – they would be at higher risk of heart disease. Participants completed measures of responses to the message and behaviour-specific cognitions (e.g., self-efficacy) for meeting the recommendations. This prospective randomized study comprised an online questionnaire and a brief follow-up 1 week later. Using an automated algorithm within the website programming, participants were randomly assigned to either the control (n = 62) or self-affirmation condition (n = 61) in a between-subjects design. All participants were then exposed to information about physical activity and heart disease before completing T1 measures. One week later, participants were invited by email to report their physical activity over the intervening 7 days.