Head Kinematic Measurements and Finite Element Modelling of Canadian Armed Forces Operators Firing Three Long-Range Rifle Configurations

Mild traumatic brain injury (mTBI) symptoms have been associated with repeated exposure to the recoil of long-range rifles. However, there is limited physical data on head responses to rifle recoil and no consistent approach to quantitatively compare rifle configurations that may mitigate head response to recoil. In the present study, the head kinematics of Canadian Armed Forces volunteers firing long-range rifles were measured and used as input to a finite element (FE) head model, enabling comparisons across different operators and rifle configurations. Head kinematics were measured with instrumented mouthguards for three rifle configurations: a 0.50 calibre rifle, a 0.338 calibre rifle, and a 0.338 calibre rifle with a recoil mitigation system (RMS). Measured head kinematics were used as boundary conditions to an FE head model to calculate brain tissue strains resulting from recoil, which were quantified using cumulative strain volume (CSV) curves. It was found that the 0.50 calibre rifle induced significantly higher strains than the 0.338 calibre rifle, while the RMS system reduced brain strain for the 0.338 calibre rifle. Characteristics such as differing anthropometrics, posture, or technique may influence brain strains, explaining the differences between volunteers. Isolating aspects of head kinematics, specifically rotation in the sagittal plane, identified it as having the largest contribution to brain strain. The findings from this study provide foundational data on the magnitudes of head kinematics experienced by volunteers when firing long-range rifles and serve as an important step towards mitigation of recoil exposures.