The impact of comfort is becoming increasingly important. On one hand, manufacturers use comfort to distinguish their products from their competitors. On the other hand, more cars than ever are used professionally. The prolonged sitting in automotive conditions of professional drivers introduced new physical complaints, resulting in high social costs. However, the cause of these complaints is not well understood. The use of virtual testing tools can contribute to both speeding up and reducing the costs of the development process of new more comfortable cars and the research in the causes of the new complaints.
Vibration loading has often been identified as a source of discomfort. In literature, several human models developed for prediction of human resonance behaviour in vibrations were described. In most of these human body models, the muscles are represented in a simplified way. However, literature specifically reports on the influence of muscle co-contraction on the human-to-seat transmissibility.
This paper presents a human body model with a detailed spinal muscle representation. Based on literature, the most important spinal muscles for stabilisation are included in the model by Hill-type elements, i.e. the rectus abdominis, the quadratus lumborum, the erector spinea, the thoracic trapezius, the obliques externum and the obliques internus. Stochastic simulations were used to investigate the interaction between the muscles on human body responses by variations in their activation levels. The simulations were based on automotive seated postures in quasi-static conditions. These stochastic simulations provided relevant information about the interaction of muscles in the spine: the simulation showed that the spine is mainly stabilised by the erector spinea, the ilias psoas, the rectus abdominus and the thoracic trapezius. Coupling of these results to dynamic applications, like vertical vibrations, showed that more research is required, especially on modelling techniques for the dynamic reaction of muscle behaviour.