The increase in vagally-mediated heart rate variability mediates treatment effects of exercise on global symptom severity across diagnostically heterogenous mental disorders: A secondary analysis of the ImPuls trial

Background: The reduced ability to adaptively respond to stressors (coping) has been proposed as an underlying mechanism across psychopathology. It is associated with a reduced vagally-mediated heart rate variability (vmHRV) at rest and increased perceived stress. The present study investigated the increase in vmHRV and the reduction in perceived stress as potential mediators of the previously demonstrated intervention effect of exercise on global symptom severity across diagnostically heterogeneous mental disorders. Methods: Sedentary outpatients with depressive disorders, anxiety disorders, insomnia and attention deficit hy-peractivity disorder were randomly assigned to a 12-week standardized exercise intervention (n = 38) or passive control condition (n = 36). Baseline and post-treatment assessments included measures of global symptom severity (Symptom Checklist-90), resting vmHRV (root mean square of successive differences between normal heartbeats), and perceived stress (Perceived Stress Scale). Intention-to-treat analyses were conducted using linear mixed models and structural equations modeling.Results: Among the intervention group, resting vmHRV increased significantly (d = 0.87, p = .003) but perceived stress did not show a significant reduction (d =-0.32, p = .267) compared to the control group. The increase in vmHRV partially mediated the intervention effect on global symptom severity (ss =-0.05, p = .013).Conclusion: The study results provide evidence that an increase in vmHRV potentially acts as a partial mediator for the beneficial effects of exercise interventions on symptoms across individuals with mental disorders who may have a diminished ability to cope with stressors.