Experimental and Numerical Studies of Muscular Activations of Bracing Occupant

Occupants who recognize the approaching crash tend to brace themselves. This reflexive muscular activation can affect the kinematics and kinetics of the occupant during the crash event but the mechanisms of potential muscle contraction in the car crash event remains poorly understood. A quantitative investigation of muscular activation has been attempted by utilizing dynamometer, sled and EMG devices with human volunteers. The experimental findings have been incorporated into the numerical investigation by utilizing a finite element model of the skeletal muscular structure of the human body. Eight male subjects were employed and the maximum amount of voluntary isometric muscular contraction for each limb joint at various joint angles was determined using a dynamometer and surface EMG. To mimic the approaching frontal crash and bracing, each volunteer was asked to brace himself when descending in the inclined sled system began. During bracing, steering wheel and pedal forces were measured as well as the EMG signals at the volunteer’s shoulder, elbow, wrist, knee and ankle joints. The pressure distributions between volunteer and seat back were also measured using a pressure mat. Simulation of muscle activation for the bracing occupant was performed using an optimization process for the joint muscle force calculations. The musculo-skeletal model with the optimized muscle parameters was utilized to validate its tensing behavior against the experimental results. The computed axial compressive loads on the steering wheel were respectively 144N and 178N for two sled heights, which correlates quite well with the average value of test measurements (121.7±46.6N and 151.1±78.9N). The computed reaction forces at pedal and seat back also exhibited quite good agreement with the test measurements.