Messages to promote physical activity: Are descriptors of required duration and intensity related to intentions to be more active?

INTRODUCTION: Mass-media campaigns such as, “Change4Life’ in the UK and “get active America” in the US, promote physical activity (PA) recommendations of at least 150 min/week of moderate-to-vigorous PA (MVPA). We investigated whether different messages used in MVPA campaigns were associated with intention to engage in more MVPA. MATERIALS AND METHODS: Theory of planned behavior (TPB) constructs; subjective norms, affective attitudes, instrumental attitudes and perceived behavioral control (PBC) were applied to explain the associations between campaign messages and intentions to engage in more MVPA. RESULTS: A total of 1412 UK adults completed an online survey on MVPA and TPB. The sample was 70% female and 93% white with 23% reporting meeting PA guidelines. Participants received one of three messages: A walking message either with or without the 150 min/week threshold (WalkT; WalkNT); a physiological description of MVPA with the 150 min/week threshold (PhysT). ANCOVA examined group differences in intention. Path analysis evaluated mediation by TPB variables. ANCOVA identified lower intentions to increase MVPA in group PhysT relative to WalkT and WalkNT (P < 0.001). PBC mediated this relationship in WalkT (β = 0.014, 95% confidence interval [CI] = 0.004–0.028) whereas affective attitudes mediated this relationship in WalkNT (β = 0.059, 95% CI = 0.006–0.113). CONCLUSIONS: Campaigns promoting MVPA guidelines need to choose their messages carefully. Messages which exemplified MVPA through walking were associated with higher intentions to increase MVPA than messages using a physiological description. Further, PBC was enhanced when the 150 min/week threshold was promoted alongside the walking exemplar. Future exemplars should be investigated to inform adults how to meet MVPA guidelines.