JMIR Publications

ABSTRACT

Background:

Social exchange processes such as social support and social control can promote health behaviour change. However, these processes are often neglected when studying health behaviour change and designing interventions. Intervening on these social exchange processes using dyadic interventions may provide a promising approach to promote health behaviours.

Objective:

This study aimed to investigate the effects of dyadic interventions to increase moderate-to-vigorous physical activity (MVPA) in romantic couples. Furthermore, we explored how the target, type, and timing of the interventions affect their effectiveness.

Methods:

Thirty-eight romantic couples (Mage = 34.01; SDage = 11.03) participated in a micro-randomised trial over 55 days consisting of control and intervention phases. The dyadic interventions included a one-time psychoeducation intervention, weekly dyadic and collaborative planning, and dyadic just-in-time adaptive interventions (JITAIs). All relevant psychological and social constructs were assessed through daily diaries. MVPA was measured through daily diaries and wrist-worn accelerometers. We used multilevel modelling to estimate the effect of the intervention phase and weighted and centred estimation for micro-randomised trials to estimate the treatment effects of dyadic and collaborative planning as well as the dyadic JITAIs.

Results:

Participants indicated higher device-based (b = 5.88, t(3665) = 1.93, P = .03) and self-reported (b = 8.26, t(3904) = 2.13, P = .01) MVPA during the intervention phase compared to the control phase. Dyadic and collaborative planning did not increase the device-based (b = 6.31, SE = 5.18, P = .12) but the self-reported (b = 14.25, SE = 5.16, P = .005) MVPA. However, the effect of planning on self-reported MVPA was not robust when additional covariates were included (b = 0.14, SE = 3.32, P = .48). Furthermore, there were positive effects of the dyadic JITAIs targeting both the actor and the partner on device-based (actor: b = 11.17, SE = 3.18, P < 0.001; partner: b = 7.23, SE = 3.60, P = 0.03) and self-reported (actor: b = 17.34, SE = 3.65, P < 0.001; partner: b = 11.82, SE = 4.10, P < 0.001) MVPA. However, the effects of the dyadic JITAIs targeting the actor disappeared for the self-reported MVPA (b = 2.20, SE = 3.22, P = 0.25) when additional covariates were added. Exploratory analyses showed that different types and timings of the dyadic JITAIs were differently effective.

Conclusions:

The current study demonstrated the promising effects of dyadic interventions to promote MVPA and highlighted the importance of the target, type, and timing of the interventions. Further research should investigate the mechanisms underlying the effects of dyadic interventions on health behaviours. Clinical Trial: The current study has been preregistered on OSF (see https://osf.io/q3vmu/?view_only=6d3511c5871e4c5799b1672d0a143de7). Furthermore, the description of the pilot study of the Time and Ties project can be found on OSF (see https://osf.io/d98yp/?view_only=2c529831f4ed4a09b82295a819dd66fe).