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In vehicle-pedestrian collisions, lower extremities of pedestrians are frequently impacted by the vehicle front structure. The aim of the current study is to understand the role of muscle activity in knee joint injuries at low velocity lateral impacts, characteristic of vehicle-pedestrian collisions. Therefore, a group of muscles in the lower extremity are modeled using bar elements with the Hill material model. The reflex response of the muscle is then included. Simulations indicate that muscle activation decreases the probability of failure in knee ligaments.

Pedestrian protection systems, both active and passive systems, are being introduced in the EU and Japan to comply with regulatory requirements. Their designs are specific and, in general, reflect an accident scenario of the pedestrian being struck on the side by a vehicle traveling at a maximum travel speed of 40 kph. The present study is an effort to quantify the effects of pedestrian reaction prior to an accident and identify characteristics that may help minimize or prevent the pedestrian to vehicle interaction. Accident situations were simulated with volunteers using a non-impacting methodology. Fifty one reactions from 23 volunteers of two age groups were observed. Most of the volunteers were found to run, step-back or stop in fright in a dangerous situation. Volunteer speed was an important parameter which could help in differentiating these reactions. Age related differences were also observed, both for reaction strategy and reaction times.

Finite Element simulation of a lower extremity model is used to (1) determine which of the muscle parameters maximum force capacity (Fmax), initial activation levels (Na) and maximum muscle contraction velocity (Vmax) affect ligament strains the most and (2) to identify which muscles affect the knee response the most in low speed, just below the knee, lateral impact. Simulations have been performed with Fmax, Na and Vmax varying from their reference values. Sensitivity of ligament strains to variation in muscle parameters has been studied. It is observed that knee response is more sensitive to Fmax and Na than Vmax. Amongst the muscles varied, reduction in the Fmax and the Na in the hamstring and the gastrocnemius muscles affects the knee ligament strains the most. The hamstring parameters significantly affects the ACL, the PCL as well as the MCL strains whereas, change in the gastrocnemius parameters affects only the MCL strain.