Effect of a stress management intervention on 24h-hrv-results from the man-go randomized controlled trial

Objective: The central autonomic network (CAN) reflects the capacity of the body to adapt to environmental challenges such as work demands. The activity of the CAN is indexed by heart rate variability (HRV), which also correlates with measures of stress at work, physical and mental health and predicts mortality. A large, 12‐month onsite randomized controlled trial to improve stress management skills at work was conducted to test the effects on HRV. Material and methods: A total of 174 lower management employees from a truck production company in Southern Germany were randomized to intervention (IG) or waiting list control group (CG). The IG received a stress management training (two days of training, half day booster after 4 and 6 months). Due to missing measurements, dropout, cardiac diagnoses and artifacts, the final sample contained N=153 (pre) and N=145 (post) participants. Stress reactivity was assessed using the Stress Reactivity Scale (SRS) and 24h HRV measurement using Schiller MediLog were conducted pre and at 12 months post intervention. Average heart rate (HR), RMSSD, and SDANN were calculated for 24h and night time. Age‐adjusted multilevel‐mixed effects linear regressions with unstructured covariance and time as random coefficient as well as time X group interaction with according Likelihood‐ratio tests were calculated. Results: No statistically significant main effects were found for HR, HRnight, RMSSD, RMSSDnight. Also, models did not improve significantly when adding the interaction. Significant reduction in SDANN24 were found for both groups (no interaction). Significant increase for the IG and reduction for CG in SDANNnight were observed (LR chi2(1) =4.11; p=0.04). Significant decrease was observed for both groups in SRS (LR chi2(1) =4.63; p=0.03), but was more pronounced in the intervention group. Conclusion: The training reduced successfully stress in both self‐reported (SRS) and objective (psychophysiology HRV) measures. Though the effects are small and visible only during the night, it is highly remarkable that three days of intervention in one year of life achieved a measurable effect, as stress is only one of many factors that influence HRV. RMSSD also showed no effects, but RMSSD represents only parts of the Vagus nerve, while SDANN reflects a broader range of autonomic reactions including circadian variation.