The effect of dynamic and static norm messages on physical activity behaviours: Evidence from two experimental studies.

Evidence suggests that dynamic norm messages, which communicate a positive collective change in behaviour over time, are more effective for changing some behaviours than messages that highlight current normative behaviour (i.e. static norm messages). However, it is unclear whether this is true for physical activity behaviours. We sought to advance understanding by testing this in two pre-registered experiments with mixed designs. In Study 1 (N = 105), we assessed the effects of the two types of messages on young adults' performance (distance travelled) and exertion (maximum and average heart rate) during a cycling task. In Study 2 (N = 163), we assessed their effects on older adults' physical activity interest, intentions and self-reported weekly activity. Static norm messages consistently had stronger effects on behaviour than dynamic norm messages, leading to greater improvements in exercise task performance and total weekly physical activity. There was also some evidence that both types of messages boosted physical activity outcomes indirectly via their positive impact on motivation and self-efficacy. Findings suggest that communicating current norms in a way that either provides people with a 'target' to aim for or that speaks to the proportion of others that are outdoing them can be particularly effective for improving physical activity behaviours.