Using accelerometry and heart rate data for non-metabolic stress modelling and real-time monitoring of soldiers’ stress in dynamic military virtual reality scenario’s

Purpose: Real-time physiological stress monitoring would be a relevant addition to virtual reality (VR) training for high-risk professions, such as the military. VR is highly suitable for the implementation of such monitoring due to the controlled environment and the already used wearables. However, physiological stress measurements suffer from distortion due to physical activity. Methods: Therefore, we tested in a first experiment whether we can use accelerometry – placed by a single accelerometer sensor at the hip of the soldier - to correct non-invasively measured heart rate (HR) for physical activity in 23 soldiers who performed three close-quarters battle (CQB) VR scenarios. These scenarios were dynamic, in that soldiers moved around in the VR environment and conducting their standard CQB procedures induced by VR simulation. In a second experiment, we placed extra accelerometer sensors also on the feet, shoulder and hands; and added some extra standard movements as reference for normal vs. typical CQB movement behavior. Results: In contrast to uncorrected HR, and HR corrected by subtracting baseline HR measured when walking, the accelerometry corrected HR was able to significantly predict the participants’ selfreported stress in the scenarios, p = 0.047, R2 = 0.11 in the first experiment. Whereas uncorrected HR significantly predicted self-reported physical demand, p = 0.028, R2 = 0.09, the accelerometrycorrected HR did not. All HR measures significantly predicted self-reported mental effort, which was most strongly the case for uncorrected HR, p < 0.001 R2 = 0.42. The second experiment showed that placing extra accelerometer sensors in combination with adding some extra movements improved our non-metabolic stress model. Conclusions: These findings, in combination with the methods’ low sensitivity to motion artifacts and non-invasiveness, are very promising for its use to monitor stress in real-time during dynamic VR training scenarios. Military Impact: Real-time physiological stress monitoring using virtual reality can have a significant impact on the military, particularly in terms of improving the performance and well-being of soldiers. This CQB VR scenario can be used or further improved to simulate high-stress combat scenarios, allowing soldiers to practice their skills in a safe environment. By monitoring physiological stress responses during training, commanders, instructors and/or mental coaches can identify areas where soldiers may need additional support or training. In addition, this VR CQB test platform seems sensitive enough to also measure the effects of applicable Human Augmentation technologies, which will be further discussed during the presentation on the ICSPP in London.