Effects of Working Environment Factors and Operator Experience on Upper Extremity Mechanical Properties During Powered Hand Tool Use

OCCUPATIONAL APPLICATIONS Powered hand tools are widely used during assembly operations. The hand displacement during powered hand-tool use has been identified as a potential risk factor for upper extremity musculoskeletal disorders. In the current study, the mechanical properties of the upper extremity were identified, which represent muscle capacity to react to an impulsive power tool torque loading and affect the responsive hand displacement. These properties were obtained from among experienced and inexperienced participants under various operating configurations, including working heights, horizontal working distances, tool moments of inertia, and joint type. The results indicated that operating configurations and experiences affected the mechanical properties of upper extremities in different ways. This research may help in future studies on powered hand-tool work-station design, for example by improving parameters in biomechanical models. TECHNICAL ABSTRACT Rationale: Hand-tool displacement during powered hand-tool use is a potential risk factor for upper extremity injuries and is correlated to the subjective discomfort level. The upper extremity has been modeled as a second-order linear system to describe the hand-tool response. While previous studies have found that working environment factors and operator experience significantly affect the hand-tool response during powered tool use, how those factors affect the mechanical properties of the upper extremity has not been investigated. Purpose: This study assessed the mechanical properties of the upper extremity under various working environment factors and operator experience levels. Method: A least-squares method was used to identify the mechanical properties of the upper extremity during powered hand-tool use, directly from the dynamics of hand-tool response. Results: Working heights, horizontal working distances, hand tool moments of inertia, joint type, and experience significantly affected some mechanical properties of the upper extremities in various operating configurations. In addition, stiffness and damping coefficients of the upper extremities were greater than those values identified from a free oscillation system in a previous study. Conclusions: Mechanical properties of the upper extremities can be used to predict hand displacement during powered hand-tool use. The current results provide additional information to improve the understanding of operator reactions to powered hand tools.