Distributed biodynamic characteristics of the human hand-arm system coupled with vibrating handles and power tools

Clinical and epidemiological studies have shown that operators of hand-held power tools are prone to develop peripheral, vascular, neurological and musculoskeletal disorders collectively known as hand-arm vibration syndrome (HAYS). The reported biodynamic responses of the human hand-arm to hand-transmitted vibration exhibit considerable differences, which could be partly attributed to the complexity of the hand-arm system. Furthermore, the vast majority of the hand-arm models offer limited applicability to the tools since these lack consideration of the anthropometric, anatomical and biological properties of the hand-arm system. Experimental and analytical methods are used in this dissertation research to: (i) identify sources of discrepancies in the reported hand-arm biodynamic responses to vibration; (ii) simultaneously characterize localized vibration transmission to different segments of the human hand-arm and the driving-point mechanical impedance (DPMI) response under different hand-arm postures, hand forces, and excitation levels; (iii) develop biomechanical models corresponding to bent- and extended-arm postures on the basis of both the DPMI and vibration transmissibility responses; and (iv) characterize vibration power absorption (VPA) distribution of different components of the hand-arm for potential injury risks assessments. The results show that the discrepancies in the reported biodynamic responses above 500 Hz were due to acceleration measurement location, handle dynamics (handle resonant frequency and deformation) and ineffectiveness of handle inertia correction. The peaks and valleys in the DPMI magnitude correspond to resonant frequencies of the tissues/muscles and the bones/structure, respectively. On the other hand, the peaks in transmissibility magnitudes represent the resonant frequencies of both the tissues/muscles and bones/structure. Furthermore, the DPMI seems to characterize the dynamic response of the entire hand-arm system with emphasis around the driving-point, while the transmissibility responses emphasize the dynamic response of the tissues/muscles of the human hand-arm system. The VPA distributions in the forearm and upper-arm were observed to be considerably higher than those of the hand components below 100 Hz, while the VPA distribution in the fingers was greater above 100 Hz. The overall results suggest the need for two frequency-weightings for assessing the potential risks due to tools with low and high frequency vibrations