Musculo-tendinous stiffness of the in vivo head-neck segment in response to quick-releases: A reproducibility study

This study was designed to assess the reproducibility of head-neck musculo-tendinous stiffness (HMS) findings of the head-neck segment in response to quick-release in flexion and extension. The HMS was expressed as the slope of the isometric torque-angular displacement curve of the head-neck segment derived from the first 15 ms from the peak acceleration following release at different exertion levels (10% to 80% MVC). A test--retest methodology (7 days interval) was performed to assess the measurement reproducibility. The results showed a linear relationship between the flexion and extension torque and angular displacement (0.94 < R $^{2} $ < 0.99). Moreover, HMS findings evidenced good to excellent reproducibility using relative (ICC) as well as absolute (SEM) parameters. It was concluded that that simple kinematic assessment was appropriate for investigating HMS. Nevertheless, multiple-segmentation of the head-neck segment could lead, according to exertion level, to geometrical changes after the release.