Role of Rotated Head Postures on Volunteer Kinematics and Muscle Activity in Braking Scenarios Performed on a Driving Simulator

Abstract

Occupants exposed to low or moderate crash events can already suffer from whiplash-associated disorders leading to severe and long-lasting symptoms. However, the underlying injury mechanisms and the role of muscle activity are not fully clear. Potential increases in injury risk of non-nominal postures, i.e., rotated head, cannot be evaluated in detail due to the lack of experimental data. Examining changes in neck muscle activity to hold and stabilize the head in a rotated position during pre-crash scenarios might provide a deeper understanding of muscle reflex contributions and injury mechanisms. In this study, the influence of two different head postures (nominal vs. rotation of the head by about 63 ± 9° to the right) on neck muscle activity and head kinematics was investigated in simulated braking experiments inside a driving simulator. The braking scenario was implemented by visualization of the virtual scene using head-mounted displays and a combined translational-rotational platform motion. Kinematics of seventeen healthy subjects was tracked using 3D motion capturing. Surface electromyography were used to quantify muscle activity of left and right sternocleidomastoideus (SCM) and trapezius (TRP) muscles. The results show clear evidence that rotated head postures affect the static as well as the dynamic behavior of muscle activity during the virtual braking event. With head turned to the right, the contralateral left muscles yielded higher base activation and delayed muscle onset times. In contrast, right muscles had much lower activations and showed no relevant changes in muscle activation between nominal and rotated head position. The observed delayed muscle onset times and increased asymmetrical muscle activation patterns in the rotated head position are assumed to affect injury mechanisms. This could explain the prevalence of rotated head postures during a crash reported by patients suffering from WAD. The results can be used for validating the active behavior of human body models in braking simulations with nominal and rotated head postures, and to gain a deeper understanding of neck injury mechanisms.

Dynamic human body models in vehicle safety: An overview

“…While the safety system dramatically reduced the impact of the head, the differences in peak head acceleration between the different types of models were larger than the differences due to anthropometry alone. Since the risk of injury can also vary with posture in the pre‐crash phase [55], our second case study focused on tuning a head‐neck reflex controller specifically [56] and simulating pre‐crash scenarios in general. In both cases, these tasks required multibody models, such as Madymo [36], as the cost of performing thousands of finite element simulations would have been prohibitive.…”

“…In a volunteer test study approved by the local ethical committee, the behavior of 17 typical participants was investigated during a mixed reality braking scenario. The participants were asked to look ahead (nom), or to the right (sho) (see photos in Figure 18A), so that their movements and muscle activity could be studied [53,56]. As in other volunteer studies, a large variability in the volunteers' behavior can be observed (Figure 18A,B).…”

“…A Driver‐in‐the‐Loop (DiL) simulator [20,52,56] makes it possible to systematically study the effects of posture [55] during the pre‐crash phase, while making laboratory‐quality measurements of participant kinematics and muscle activity. In a volunteer test study approved by the local ethical committee, the behavior of 17 typical participants was investigated during a mixed reality braking scenario.…”

Dynamic Human Body Models in Vehicle Safety: An Overview

“…The passive properties of the AHBM have been validated using PMHS tests [113]. Many active properties of the model have been indirectly validated by comparing the response of the entire head and neck model to in-vivo sled tests [9,14,56], Driver-in-the-Loop (DiL) tests [20,51,53], and tests in real vehicles [42,91]. An overview of available tests is provided by the OSCCAR consortium [88].…”

“…DiL test allows to put the occupant into new (virtually) interior concepts while exposed to a mixed-reality scenario and to study the interaction under (limited) external loading. Different test series, see [50,53,20] were performed to gain a better understanding of human behavior in such situations. To analyze the driver's behavior in experiments, the kinematics and muscle activation are monitored, see Fig.…”