Do increases in physical activity encourage positive beliefs about further change in the ProActive cohort?

Effects of behaviour change on cognitions are rarely examined within the Theory of Planned Behaviour. We tested whether increases in physical activity resulted in more positive beliefs about further change among a cohort of sedentary adults participating in a behavioural intervention trial (ProActive). At baseline, 6 and 12 months, 365 adults completed questionnaires assessing physical activity and cognitions about becoming more active over the coming year. Objective activity was assessed at baseline and 12 months. Participants reporting larger increases in activity were no more positive about making further increases than those reporting less behaviour change (p-values>0.05). Participants with larger increases in objective activity reported weaker perceived control (β=-0.342; p=0.001) and more negative instrumental attitudes (β=-0.230; p=0.017) at 12 months. Participants may have felt that they had changed enough or measures of perceived success may be more sensitive to behaviour change. Alternatively, long measurement intervals may have missed immediate cognitive and affective consequences of behaviour change, or such effects may require participants to consistently self-monitor or receive feedback on performance. Future studies could test the effect of such techniques on physical activity and a wider range of cognitive, affective and physiological consequences, using more frequent measurement intervals.