Head impact accelerations for brain strain-related responses in contact sports: a model-based investigation

Both linear $$(\mathbf{a}_{\mathrm{lin}})$$(alin) and rotational $$(\mathbf{a}_{\mathrm{rot}} )$$(arot) accelerations contribute to head impacts on the field in contact sports; however, they are often isolated in injury studies. It is critical to evaluate the feasibility of estimating brain responses using isolated instead of full degrees-of-freedom (DOFs) accelerations. In this study, we investigated the sensitivities of regional brain strain-related responses to resultant $$\mathbf{a}_{\mathrm{lin}}$$alin and $$\mathbf{a}_{\mathrm{rot}}$$arot as well as the relative contributions of these acceleration components to the responses via random sampling and linear regression using parameterized, triangulated head impacts with kinematic variable values based on on-field measurements. Two independently established and validated finite element models of the human head were employed to evaluate model-consistency and dependency in results: the Dartmouth Head Injury Model and Simulated Injury Monitor. For the majority of the brain, volume-weighted regional peak strain, strain rate, and von Mises stress accumulated from the simulation significantly correlated with the product of the magnitude and duration of $$\mathbf{a}_{\mathrm{rot}}$$arot, or effectively, the rotational velocity, but not to $$\mathbf{a}_{\mathrm{lin}}$$alin. Responses from $$\mathbf{a}_{\mathrm{rot}}$$arot-only were comparable to the full-DOF counterparts especially when normalized by injury-causing thresholds (e.g., volume fractions of large differences virtually diminished (i.e., $$<$$<1 %) at typical difference percentage levels of 1–4 % on average). These model-consistent results support the inclusion of both rotational acceleration magnitude and duration into kinematics-based injury metrics and demonstrate the feasibility of estimating strain-related responses from isolated $$\mathbf{a}_{\mathrm{rot}}$$arot for analyses of strain-induced injury relevant to contact sports without significant loss of accuracy, especially for the cerebrum.