Figure 1.

Angular impulse contributions during simulated mild head impacts. Impacts were divided into an acceleration and deceleration phase based on the planar angular acceleration time history (positive acceleration is the sagittal extension of lateral flexion towards the non-dominant side). We included a short 30 ms of zero force pre-load to allow the model to reach a balanced steady state (pre-motion). In some conditions, head stabilization was achieved before the end of the 300 ms impact simulation, resulting in a post-motion period with low angular accelerations (|α| < 10 rad s⁻²). Impulse contributions during acceleration and deceleration phases were computed for external load, gravity, all muscles (active component), all muscles (passive component) and all ligaments for each condition and aggregated over all subjects. Angular impulse contributions were also normalized by total angular impulse produced by the external force. When neck muscles were relaxed, ligaments and passive muscles had the largest angular impulse contribution in deceleration for (a) sagittal extension and (c) coronal lateral flexion, respectively. When neck muscles were cocontracted, the active muscle had the largest angular impulse contribution in deceleration for both (b) sagittal extension and (d) coronal lateral flexion. In all cases, external load provided the angular impulse that accelerated the head, with active muscles providing over 30% resistive angular impulse during cocontracted muscle cases. (Online version in colour.)