Effects of Bracing on Human Kinematics in Low-Speed Frontal Sled Tests

Abstract

Continued development of computational models and biofidelic anthropomorphic test devices (ATDs) necessitates further analysis of the effects of bracing on an occupant's biomechanical response in automobile collisions. A total of 20 dynamic sled tests were performed, 10 low (2.5 g, Δv = 4.8 kph) and 10 medium severity (5.0 g, Δv = 9.7 kph), with five male human volunteers of approximately 50th percentile male height and weight. Each volunteer was exposed to two impulses at each severity, one relaxed and one braced prior to the impulse. A Vicon motion analysis system, 12 MX-T20 2 megapixel cameras, was used to quantify subject 3D kinematics (±1 mm) (1 kHz). Excursions of select anatomical regions were normalized to their respective initial positions and compared by test condition. At the low severity, bracing significantly reduced (p < 0.05) the forward excursion of the knees, hips, elbows, shoulders, and head (average 35-70%). At the medium severity, bracing significantly reduced (p < 0.05) the forward excursion of the elbows, shoulders, and head (average 36-69%). Although not significant, bracing at the medium severity considerably reduced the forward excursion of the knees and hips (average 18-26%). This study illustrates that bracing has a significant influence on the biomechanical response of human occupants in frontal sled tests and provides novel biomechanical data that can be used to refine and validate computational models and ATDs used to assess injury risk in automotive collisions.

A Novel Approach to Measuring Muscle Mechanics in Vehicle Collision Conditions

“…Three low-velocity impact scenarios were tested: low (1.7 g), medium (2.6 g), and high (3.8 g) impact pulse. The sled impact pulse was within the range of other studies on the volunteer dynamic response in frontal impacts, such as those by Beeman et al (2.5–4.7g) [2] and Seacrist et al (3.8 g) [36], who used inverse dynamics analysis of the neck loads, as well as other experimental and numerical studies on the neck muscle activity [5,8,37,41,42]. Table 1 shows the average parameters (mean ± standard deviation (SD)) of the impact pulse used.…”

“…Muscle activity can affect the body posture and dynamic response of the occupant’s body in low-velocity vehicle collisions, evasive braking, and steering manoeuvres (as well as deployment of autonomous collision avoidance systems) [1,2,3,4,5,6]. Bracing and occupant body dynamics may also influence the injury outcome in low-severity impacts [7].…”

“…Anderst et al [34] used the inverse dynamics approach to estimate neck muscle forces, where in vivo motion data was used to drive a numerical model of the head-neck complex, but for slow voluntary motion only. Funk et al [35] verified that the inverse dynamics approach can be used for the neck load estimation in case of impact forces acting to the head, while Seacrist et al [36] and Beeman et al [2,3,4] analysed volunteers’ neck loads during low-velocity frontal impacts. However, the joint moment results from the action of the whole muscle group, the electrical activity of which cannot be assessed with a single EMG electrode, making it difficult to correlate the EMG signal to the body dynamic response directly.…”

Tripping Elicits Earlier and Larger Deviations in Linear Head Acceleration Compared to Slipping

“…The anatomical reference frame had an origin at the head center of gravity (CG), and was defined by the anterior-posterior (AP), medial-lateral (ML) and vertical (VER) axes when in the anatomical position. The head CG was defined as the midpoint between the right and left anterior-superior point of the helix of the outer ear [31]. The (+) ML axis was defined as a unit vector pointing from the left to right tragion, the (+) VER axis was defined as a unit vector perpendicular to a plane created by the left tragion, right tragion, and average position of the left and right infraorbitale foramen (positive from head towards ground), and the (+) AP axis was defined as perpendicular to the (+) ML and (+) VER axis [32].…”

Evaluation of the Efficacy of Head and Brain Injury Risk Functions

“…A similar study conducted by Hendler et al (1974) (Kumar et al, 2006;Zaborowski, 1964Zaborowski, , 1965) and due to barrier crashes (Bohlin, 1964). Studies have also used sled tests to characterize and compare the occupant kinematics of volunteers, PMHS, and ATDs by assessing the excursion seen by each group (Beeman et al, 2012) and to characterize the effect of bracing on the kinematics (Beeman et al, 2011;Olafsdottir et al, 2013). Arbogast et al (2009) conducted a series of non-injurious, frontal sled tests in order to quantify and compare the kinematic responses of a child to those of an adult.…”