Effects of dyadic planning on physical activity in couples: a randomized controlled trial

Objective: Action planning can help translate physical activity intentions into action by linking situational cues with behavioral responses. Dyadic planning extends action planning and refers to target persons forming plans for their own behavior change together with partners. This study investigated whether a dyadic planning intervention could increase physical activity in target persons and their partners, whether these effects were moderated by relationship quality and mediated by action control, activity-specific received partner support, and control.

Method: Couples (n = 338; target persons randomized) were randomly assigned to (a) a dyadic planning condition (DPC); (b) an individual planning condition (IPC), in which target persons planned and partners worked on a distractor task; or (c) a control condition (CC), in which couples worked on a distractor task. During 3 assessments up to 6 weeks postintervention, moderate (primary outcome) and vigorous activity were objectively measured; other variables were self-reported. Multilevel and path models were fit.

Results: There were no beneficial direct effects of the intervention for DPC target persons. Over time, DPC partners' vigorous activity increased, but decreased again. At lower relationship quality, DPC target persons' activity decreased, whereas IPC target persons' vigorous activity increased. Mediation hypotheses were not supported. Mutual influence models indicated positive effects of partners' on target persons' moderate activity in DPC and CC, whereas for IPC, negative effects of target persons' on partners' moderate activity emerged.

Conclusions: Findings revealed the complexity of effects of dyadic planning on behavior change. Adding relationship quality to the equation clarified effects of DPC and IPC on physical activity.