Biomechanical models of the human hand-arm to simulate distributed biodynamic responses for different postures

Hand-transmitted vibration and the associated potential injuries are dependent on hand-arm posture, hand forces and other factors. This study presents biomechanical models consisting different substructures of the hand-arm system and the trunk of the body in different postures subject to z-axis vibration. The trunk was considered in order to account for observed and reported considerable vibration at the shoulder and of the head. The models parameters were derived through error minimization using three different target biodynamic functions namely: driving-point mechanical impedance alone; localized vibration transmissibility responses alone; and combined simultaneously measured impedance and transmissibility responses. The results showed that the models' parameters and responses are strongly dependent on the type of the target function. The models derived using impedance or transmissibility responses target function yield good comparisons with measured impedance or transmissibility responses, respectively, but none adequately characterize both the impedance and transmissibility responses. The models based on combined impedance and transmissibility target functions yield reasonably good comparisons with both measured biodynamic responses and characteristic frequencies. The results suggest that the transmissibility responses characterize the dynamics of the local tissues/muscles of the human hand-arm at different locations, while impedance characterizes the entire hand-arm system with emphasis around the driving-point. The results showed a strong coupling between the human hand-arm system and the whole-body. Relevance to industry: Occupational exposure to hand-transmitted vibration has caused health problems in some operators of hand-held power tools. This has resulted in loss of manpower and costs in terms of compensations paid to affected workers. The existing International guidelines (ISO 5349-1, 2001) could not adequately predict some components of the hand-arm vibration syndrome due to lack of knowledge about hand-arm injury mechanism and probably due to neglect of the effect of posture adopted by workers in the assessment method. The biomechanical models for different postures presented in this study could be used to estimate distributed biodynamic responses (vibration power, dynamic forces, vibration intensity and deformation of joints) of the human hand-arm system exposed to vibration. Potential injury assessment based on these distributed biodynamic responses may yield better prediction of different components of the hand-arm injury and enhance understanding of injury mechanism. (C) 2012 Elsevier B.V. All rights reserved.