Effect of high level grip-and push force and elevated arm posture on the zh-axis hand-arm impedance

In this study, we investigated the effect of grip forces, push forces and two arm postures on the biodynamic response of the human hand-arm system for vibration excitation along the forearm axis. Knowledge about the biodynamic response, in this case the mechanical impedance, is important for understanding the dynamic human-machine interaction and developing human models. The current state of research lacks information about the effect of high grip forces, push forces, and an overhead hand-arm posture on the mechanical impedance. In this study, we measured the mechanical impedance of 30 subjects with an electromechanical shaker in translational direction along the forearm axis. We investigated the influence of grip-forces (30 & 135 N), push-forces (50 & 110 N), arm postures (shoulder flexion 0 degrees & 90 degrees) as well as the respective effect sizes in the range of 10-500 Hz. The investigated factors have a significant influence (p < .01) depending on the vibration frequency. The arm posture had a significant influence in the low frequency range with a weak effect size, while push forces affected the MI in a medium frequency range with a medium to strong effect size. Grip forces had a strong effect at low and high frequencies. The findings from this study contribute to the general understanding of hand-arm dynamics but also serve as an input for the development of mechanical and simulation models of the human hand-arm system which can be used to assess vibrations during development of hand held machinery.