A biodynamic model of human reaction to impulsive torques encountered in hand tools

The human tool operator was modeled as a one degree of freedom mechanical torsion system in order to predict human capacity to react against large non-harmonic forces. Such a practical model can be used to design better hand tools and industrial tasks that minimize the risk of upper limb disorders by predicting the kinetic and kinematic responses of the body to impulsive torques in hand tool use for a given population. A standing operator grasping a tool handle was therefore mechanically represented as mass, spring and damper elements. The values of these elements were dependent upon body posture and the individual operator. The apparatus used to quantify the model parameters measured the response change of a known mechanical system by the external loading of the hand and arm during free vibration frequency and amplitude decay. Twenty-five subjects were tested in a repeated measures experiment for factors representative of actual workplace conditions including hand horizontal location, hand vertical location, handle shape and tool orientation.