Study On Mechanism And Modeling Method Of Driver's Back Muscle Response Under Whole Body Vibration

Whole body vibration is the key cause of rapid fatigue of the driver's muscles and low back pain.Vibration-induced stretch reflex of the muscle is considered to be the intrinsic mechanism.This paper creates a driver's musculoskeletal biomechanical model that can calculate the back muscles' response under whole body vibration,and evaluate the driver's vibration comfort from the perspective of biomechanical load.The established vibration comfort simulation platform can quantitatively evaluate the driver's back muscle response under different vibration inputs,which lays a theoretical foundation for improving the comfort design of the car and has important engineering application value.Based on the physiological anatomical data in the literature,a human cervical spine model conforming to the natural physiological curve of the human body is established which improved the generalization ability and prediction accuracy of the cervical vertebra model.Then combined with the lumbar and thoracic spine models established by Meng and Dennis,the human spine system musculoskeletal model was established.Then the dynamic characteristics of intervertebral soft tissue are considered in our model.An optimal selection algorithm based on mixed-effct model regression analysis is proposed.A three-order nonlinear intervertebral stiffness model with stronger generalization ability is constructed for each joint of the spine,which solved the problem of the input of model and joint angle mismatch.Finally,based on force dependent kinematic method,an optimization method for the prediction of the rotational displacement of each joint is proposed,which realizes the prediction of the intervertebral joint rotation angle under arbitrary posture,and the model prediction result is consistent with the experimental measurement value and has high accuracy.The effect of stretch reflex on the vibration response of human muscles under different vibration frequencies is studied by conducting vibrational stretch experiment using the gastrocnemius muscle of SD rats.The experiment finds that stretch reflex has a significant effect on muscle vibration response,and the muscle force decreases by more than 20% after cutting off the stretch reflex.It implies that the vibration induces stretch reflex which lead muscle generate active muscle force.The active force combined the passive tension increases the biomechanical loads of the muscle,which accelerating the development of muscle fatigue.In addition,under the control of stretch reflex,the muscle response force under vibraion exhibits hysteresis-damping characteristics with the change of muscle length,and exhibits frequency-dependent nonlinear characteristics.The research supports the modeling of stretch reflex,which provides theoretical support for human musculoskeletal modeling and dynamics simulation under whole body vibration.The vibration response of the driver's back muscles under different frequency sinusoidal vibrations is studied by conducting whole body vibration experiment.It finds that the amplitude of EMG of the erector spinae muscles reached the peak at the resonance frequency around 4 Hz.Subsequently,the driver's lumbar intervertebral stiffness and the mechanical characteristics of the human-chair contact system were modeled.Combined with the developed stretch reflex delay feedback control model,the driver's vibration comfort considering the nonlinear dependence of the muscle stretch reflex frequency was established.The model predicted muscle activation reached its maximum near the resonance frequency of the human body system,consistent with the experimental results.It confirms the mechanism that the human skeletal muscle is induced to stretch and reflex under the vibration of the seat,forcing the skeletal muscle activation to be greatly improved,resulting in a substantial increase in muscle load,thereby accelerating muscle fatigue.