Influence of active muscle contribution on the injury response of restrained car occupants.

Optimal performance of adaptive restraint systems requires an accurate assessment of occupant parameters including physical properties and pre-collision behavior of the occupant. Muscle bracing, one of the key reflexive actions adopted by car occupants to mitigate the severity of an impending collision, is ignored in restraint designing since conventional human surrogate tools used for injury assessment due to collision loading provide limited insight into this effect. This study is aimed at evaluating the effect of pre-collision muscle bracing on the injury outcome of an occupant using a simplified numerical musculoskeletal model. The activation levels for 12 major muscle groups loading the ankle, knee, hip and elbow joints, were determined using an optimization routine with data collected from previously reported volunteer sled tests. A whole body injury metric, weighted to the severity of injury and the injured body region, was used to evaluate the potential risk of injuries estimated for different levels of bracing. The musculoskeletal model was further used to determine the requirements on the restraint system properties to minimize overall injuries for an occupant in a relaxed and a braced condition. Significant variation was observed in the load-limiting value and pre-tensioner firing time, as the restraint properties were optimized to account for the bracing behavior. The results of the study provide a framework for improving the performance of adaptive restraint systems, currently designed for passive anthropometric tests devices, by taking into account realistic response of the occupant involved in a collision.