Recoil-induced mild traumatic brain injury (mTBI) – literature review

This report documents a literature study which attempts to answer whether recoil-induced mild traumatic brain injury (mTBI) is a side-effect of firearm training. Recoil-induced mTBI has not been observed in any of the published work that we have evaluated. This may be either because the recoil force is not strong enough to induce mTBI, or because the number of shots associated with each work was too small. It is, however, worth noting that members of the Canadian armed forces have verbally reported symptoms of mTBI during repeated long-range rifle firing. Based on the recorded head motion in the literature, it seems that if recoil-induced mTBI exists, then it is likely a consequence of rotational motion. On physical grounds, this makes sense as the brain’s shear modulus is much lower than its bulk modulus, i.e., the brain deforms more during rotation than translation. A smaller sample of the recorded rotational head motion overlaps with the lower mTBI thresholds. In the end, it is unclear if the reported mTBI symptoms arise due to shock loading, if they are undiagnosed mTBI from other exercises whose symptoms gets triggered by the recoil load, or if the mTBI was induced purely by repeated firing of long-range rifles. Experiments with longer shootings sessions, in combination with theoretical studies where the brain is recoil loaded by repeated firings may shed more light on this matter.