Heart rate variability detects psychophysiological stress induced by realistic force-on-force training of police personnel

Purpose: Acute tactical stress (ATS) can reduce the performance of police officers (POs) on complex tasks such as decision-making and management of emotions in self-defense situations. ATS may also suppress the ability to keep situational control. In the real world this may dramatically increase inappropriate use of force and liability. Thus realistic tactical training (RTT) is mandatory for POs and it is increasingly performed with scenarios simulating real-world force-on-force incidents (RWS), but objective methods to evaluate individual stress response to RTT are still lacking. This study aimed at evaluating the predictive accuracy (PA) of heart rate variability analysis (HRVa) to assess the amount of ATS induced in POs by RTT training including use of force skills. Methods: 12-lead ECG, respiration and physical activity were continuously monitored with a seamless garments sensor electrode and a miniaturized telemetric wireless device in 24 POs during RTT. The RWS consisted of different phases providing alternation of low- (LS) and high-stress (HS) challenges. Baseline StateTrait Anxiety and Anger were assessed with the STAI Y1-Y2 and STAXI2 questionnaires. Rating Scale Mental Effort and NASA Raw Task Load Index measured stress and workload. State Anxiety and Anger were reassessed after each RWS. Performance monitored with video cameras was scored by instructors. HRV parameters were computed in the time- and frequency-domain and with non-linear methods, from standard (300-seconds) and very-short (60-seconds) intervals. Discriminant Analysis (DA) was used to identify which parameters were more efficient to assess ATS providing separation between HS and LS. Results: All POs were in good psychological balance, with no evidence of individual tendency to respond with abnormal levels of state anxiety/anger to the test challenges. HR increment (p<0.001) was not efficient in differentiating between LS and HS. At univariate analysis several HRV features were significantly different (p<0.01) between LS and HS situations. At DA the two stress conditions were separated with a 80,4% PA even cross-validating the results, combining most significant (p<0.005) HRV features in the formula F1 = 1,156 x HRVTri − 0,018 x VLFpower – 0,061 x SD2 − 1,156 x DFα2 − 1,243 (LS if F1 >0). Conclusions: ATS induced by police RTT determines changes of cardiac autonomic modulation which are different in LS and HS scenarios. DA of HRV provides accurate assessment of stress response useful to study the relationship between stress and performance on individual basis and to design more personalized copying training