Transdiagnostic efficacy of a group exercise intervention for outpatients with heterogenous psychiatric disorders: a randomized controlled trial

Background: Exercise efficaciously reduces disorder-specific symptoms of psychiatric disorders. The current study aimed to examine the efficacy of a group exercise intervention on global symptom severity and disorder-specific symptoms among a mixed outpatient sample. Methods: Groups of inactive outpatients, waiting for psychotherapy, with depressive disorders, anxiety disorders, insomnia, and attention-deficit/hyperactivity disorders were randomized to a manualized 12-week exercise intervention, combining moderate to vigorous aerobic exercise with techniques for sustainable exercise behaviour change (n = 38, female = 71.1% (n = 27), M-age = 36.66), or a passive control group (n = 36, female = 75.0% (n = 27), M-age = 34.33). Primary outcomes were global symptom severity and disorder-specific symptoms, measured with the Symptom Checklist-90-Revised and Pittsburgh Sleep Quality Index pre- and post-treatment. Secondary outcome was the self-reported amount of exercise (Physical Activity, Exercise, and Sport Questionnaire), measured pre-treatment, intermediate-, and post-treatment. Intention-to-treat analyses were conducted using linear mixed models. Linear regressions were conducted to examine the effect of the change of exercise behaviour on the change of symptoms. Results: The intervention significantly improved global symptom severity (d = 0.77, p = .007), depression (d = 0.68, p = .015), anxiety (d = 0.87, p = .002), sleep quality (d = 0.88, p = .001), and increased the amount of exercise (d = 0.82, p < .001), compared to the control group. Post-treatment differences between groups were significant for depression (d = 0.63, p = .031), sleep quality (d = 0.61, p = .035) and the amount of exercise (d = 1.45, p < .001). Across both groups, the reduction of global symptom severity was significantly predicted by an increase of exercise (b = .35, p = .012). Conclusions: The exercise intervention showed transdiagnostic efficacy among a heterogeneous clinical sample in a realistic outpatient setting and led to sustained exercise behaviour change. Exercise may serve as an efficacious and feasible transdiagnostic treatment option improving the existing treatment gap within outpatient mental health care settings.