Musculo-tendinous stiffness of the head-neck segment for extension movement during application of quick-releases

Since head-neck segment stabilization is critical for human safety and balance control, the aim of this study was to investigate changes in musculo-tendinous stiffness of the head-neck segment during different tasks. We propose to consider the head-neck segment as a singlejoint system with a changeable geometry as proposed in [1]. The aim was to evaluate the musculo-tendinous stiffness for head extension movement. Based on kinematics and optimization procedure, different applications of quickreleases (QR) were performed at different % of Maximal Voluntary Contraction (MVC). Ten healthy subjects volunteered. A load cell instrumented by an electromagnet coupled with an Optotrak device was used to get input data for the model. After QR, the musculo-tendinous stiffness (S) was evaluated as in [2]. Results showed a significant increase of S according to the external force intensity (P<0.05). The slope of the linear regression amounted to 3.16. This slope provides the stiffness index of the head–neck segment in extension. Comparisons with flexion results were performed.