Examining the Impact of Acceptance and Commitment Therapy Intervention on Perceived Stress, Cortisol Levels, and Heart Rate Variability Among Athletes

Pellikka, V. 2024. Examining the Impact of Acceptance and Commitment Therapy Intervention on Perceived Stress, Cortisol Levels, and Heart Rate Variability Among Athletes. Faculty of Sport and Health Sciences, University of Jyväskylä. Master´s Thesis in Sports Coaching and Fitness Testing. 55 p., 7 attachments. Athletes confront continuously stressful situations for instance when preparing for competition, in performance demands, getting injured, experiencing a defeat, or stress can be general life stress. Perceived stress induces physiological alterations by heightening cortisol secretion and diminishing heart rate variability (HRV). In recent years, Acceptance and Commitment Therapy (ACT) and mindfulness-based approaches have gained increasing attention in applied sports psychology because of their effectiveness in reducing perceived stress. The study aimed to iden-tify how ACT affects athletes´ perceived stress and how subjective stress is connected to physi-ological stress markers including salivary cortisol and heart rate variability. The study was a two-group randomized control trial consisting of national-level athletes (n=28). Participants were pair-matched and randomly assigned to either a six-week Acceptance and Commitment Intervention group (INT) (n=16) or a Waitlist control group (WLC) (n=12). A between-groups pre-post (INT vs. WLC) design was implemented in the preseason. Pre-to post-intervention, both study groups completed a standard self-reported stress questionnaire (PSS-10), and salivary cortisol and HRV were measured. After the pre-measurements, the INT group took part in the ACT intervention, after which both groups conducted the same measure-ments as in the baseline. The study's primary finding was that the ACT intervention produced a statistically significant change in both groups' salivary cortisol levels (p=0.001). However, no significant differences were observed between the groups. Furthermore, athletes' salivary cortisol, or HRV did not correlate to perceived stress. Although the ACT intervention did not affect athletes´ perceived stress or physiological stress markers, the ACT may have had different performance-promoting effects on athletes. ACT interventions are studied to be effective in the sports context in enhanc-ing performance, increasing psychological well-being and executive function, and decreasing anxiety. Keywords: Acceptance and Commitment Therapy, psychological stress, physiological stress