Initial Head Posture Affects the Neck Muscle and Head/Neck Kinematic Responses During Low-Speed Rear Impacts.

Abstract

The goal of this study was to quantify the effect of initial head posture on neck muscle activity and head/neck kinematics during rear impacts. Twelve seated participants experienced rear impacts on a sled with their head in five initial driving postures: left shoulder check, left mirror check, neutral head-forward, rear-view mirror check, or looking at their front-seat passenger. Electromyographic activity in four neck muscles was recorded bilaterally with indwelling electrodes and normalized to maximum voluntary contraction (MVC) levels. Head and torso kinematics were measured. Pre-impact muscle activity increased in 6 of the 8 muscles for non-neutral postures compared to the neutral posture (Δ = 0.6-7.5% MVC). During impact, only the peak left multifidus activity significantly changed (Δ = - 12% MVC) during left mirror check compared to neutral posture. Compared to the neutral posture, we observed larger absolute head acceleration (Δ = 0.7-2.6 g) out of the sagittal plane for all non-neutral postures and smaller fore-aft head-torso displacement (Δ = 5.2-7.8 mm) in the left shoulder check and look-at-passenger postures, but only minimal changes in torso kinematics. Despite minimal changes to peak neck muscle activity during impact, we observed widespread changes in the head kinematics in non-neutral postures. This work provides data to inform injury prevention methods and simulate drivers with non-neutral head postures in computational models.