The football helmet is credited with reducing the incidence of traumatic brain injury by protecting against linear impacts. Despite this, concussion rates remain high. It is proposed that linear acceleration, used as the sole metric to measure helmet performance, may be limited for predicting concussive injury. The purpose of this study was to compare bare and helmeted headforms impacts at five impact locations and four impact directions using peak linear acceleration, peak rotational acceleration, and maximum principal strain.

The results demonstrated the individual metrics;​ peak linear acceleration, peak rotational acceleration and maximum principal strain did not significantly vary over impact condition when viewing the bare and helmeted headforms separately. When reviewing the metrics individually in terms of risk prediction, reductions observed for peak linear (76%) and peak rotational acceleration (79%) for the helmeted conditions reflected substantial decreases in the risk of concussion (25‐50% risk). Reductions for maximum principal strain (44%) were less compared to the dynamic head response results and indicate high risk of concussion (>80% risk). The reported differences in injury risk between dynamic head response values and brain tissue strains challenges the use of dynamic head response variables to measure the ability of helmets to protect against concussion.