Investigation of Brain Response in Canadian Armed Forces Volunteers Subjected to Recoil Force from Firing Long-Range Rifles Using Instrumented Mouthguards and Finite Element Head Model

Abstract

Mild traumatic brain injury (mTBI) may be caused by occupational hazards military personnel encounter, such as falls, shocks, exposure to blast overpressure events, and recoil from weapon firing. The repeated exposure of Canadian Armed Forces (CAF) members to sub-concussive events during the course of their service may lead to a significant reduction in quality of life. Symptoms may include headaches, difficulty concentrating, and noise sensitivity, impacting how personnel complete their duties and causing chronic health issues. CAF members have reported experiencing symptoms of mTBI, and some studies have associated these symptoms with repeated firing of long-range rifles. However, there is limited physical data on head response resulting from rifle recoil and different rifle configurations. The objectives of this study were to quantify head kinematics for volunteers, assess the head response using kinematic-based metrics, and assess brain response using a detailed finite element head model. Measurements of head motion were recorded in a group of military volunteers using instrumented mouthguards while firing long-range rifles. The head kinematics were then used as inputs in a finite element head model to calculate the brain strains for each firing event and assessed using common response metrics and a Cumulative Strain Volume (CSV) measure to quantify brain deformation resulting from head acceleration. The measured head kinematics and predicted brain deformation among CAF volunteers were lower than those associated with acute injury. The study highlighted the corpus callosum as the primary site of higher strains in the brain, consistent with previous research on head response to acceleration events. Brain deformation was primarily associated with angular velocity rather than linear acceleration. Comparative analysis between different rifle calibers revealed higher values of head kinematics associated with increased rifle caliber, owing to the higher level of energy. The CSV method identified statistically significant differences between rifle configurations and reductions in brain deformation with a recoil mitigation system (RMS), offering a potential solution to reduce long-term symptoms from firing long-range rifles. The results of this study offer important information about the magnitude of kinematics and strains that volunteers experience when firing long-range rifles.