  Accidentology or shock biomechanics are research domains mainly devoted to
the development of safety conditions for the users of various transport modes
in case of an accident. The objective of this study was to improve the
knowledge of the biomechanical behaviour of the lower limb facing sudden
dynamic loading during a frontal collision. We aimed at establishing the
relationship between the level of muscular activity prior to impact, called
'preactivation', of the lower limb extensors and the mechanical characteristics
of impact. Relationships were described between the level of preactivation, the
impact peak force values, the minimum force after unloading and the associated
loading and unloading rates. The existence of reflex mechanisms that were
affected by the level of voluntary muscular preactivation for the lower limb
muscles was demonstrated. In conclusion, the existence of specific mechanism
acting mainly at the knee level may result from the level of preactivation.
Muscle behavior has to be included in numerical models of the human driver to
better evaluate the overall stiffness of the body before and at impact.
