In this web-based experimental study, the investigators will use a pre-test post-test four-arm parallel design to compare the effect of promoting an active choice process versus a passive choice process about physical activity on behavioural outcomes (e.g. physical activity behaviour, perceived increase in physical activity) and psychological outcomes (e.g. physical activity intention, commitment) among physically inactive adults.~Participants will be randomized to one of four groups. Participants in group GA+ will be encouraged to make a very active choice by weighing advantages and disadvantages of physical activity, considering personal values, identifying barriers and engaging in action and coping planning. The intervention for group GA is similar, but lacks the action and coping planning exercises. In the other two groups, a passive choice process will be promoted by only providing information: Group G will read the national physical activity guideline and group GI will read the guideline and information about possible advantages and disadvantages and barriers to physical activity. Behavioural and psychological outcomes will be assessed at the first measurement and follow-up measurement. Regression analyses will be performed to examine intergroup differences. In addition, sensitivity analyses and a process evaluation will be performed.
This web-based experimental study aims to ascertain whether promoting an active (i.e. conscious and autonomous) choice process about physical activity results in better behavioural outcomes (e.g. physical activity) and psychological outcomes (e.g. physical activity intention) compared to promoting a passive choice process in physically inactive adults.