Processes of change in Acceptance and Commitment Therapy and Applied Relaxation for long‐standing pain

M.K. Kemani, H. Hesser, G.L. Olsson, M. Lekander, R.K. Wicksell

The utility of cognitive behavioural (CB) interventions for chronic pain has been supported in numerous studies. This includes Acceptance and Commitment Therapy (ACT), which has gained increased empirical support. Previous research suggests that improvements in pain catastrophizing and psychological inflexibility are related to improvements in treatment outcome in this type of treatment. Although a few studies have evaluated processes of change in CB-interventions, there is a particular need for mediation analyses that use multiple assessments to model change in mediators and outcome over time, and that incorporate the specified timeline between mediator and outcome in the data analytic model. This study used session-to-session assessments to evaluate if psychological inflexibility, catastrophizing, and pain intensity mediated the effects of treatment on pain interference. Analyses were based on data from a previously conducted randomized controlled trial (n = 60) evaluating the efficacy of ACT and Applied Relaxation (AR). A moderated mediation model based on linear mixed models was used to analyse the data. Neither catastrophizing nor pain intensity mediated changes in pain interference for any of the treatments. In contrast, psychological inflexibility mediated effects on outcome in ACT but not in AR. Results add to previous findings illustrating the role of psychological inflexibility as a mediator in ACT.