Do people with different personalities react differently to the interventions of acceptance and commitment therapy?

This study evaluated the effectiveness of Acceptance and Commitment Therapy (ACT) interventions in changing psychological flexibility processes in young physically active adults aged 20 to 25 years (N = 30). It also examined the moderating role of personality traits, measured with the Big Five Questionnaire (BFQ). Participants self-selected into either an experimental group, which completed eight weekly ACT-based interventions, or a passive control group. All participants completed the BFQ and the Multidimensional Psychological Flexibility Inventory (MPFI) at baseline. The MPFI was administered again after 10 weeks, while personality was assessed only at baseline. The study showed that at baseline, psychological flexibility processes differed between the groups, with the experimental group reporting lower flexibility. After 10 weeks, no significant differences remained. The ACT interventions were associated with a reduction in inflexibility processes in the experimental group, while the control group also showed a decrease in flexibility processes. Within the experimental group, the personality trait of dominance negatively predicted changes in most psychological flexibility processes. While previous research supports the effectiveness of ACT interventions for mental health, this study expands current understanding by focusing on a physically active young adult sample and assessing both flexibility and inflexibility processes. Personality traits, particularly dominance, may moderate ACT intervention outcomes.