Kinematics, kinetics, and psychophysical perceptions in symmetric and twisting pushing and pulling tasks

The use of material handling devices (MHDs) to eliminate the repetitive lifting components of industrial jobs has introduced a new set of issues for industrial ergonomics. Worker performance and safety when using MHDs depends on the mass and distance moved, the asymmetry of the postures, and the positioning accuracy required at each endpoint of the movement. Ten participants moved loads of up to 68 kg and placed them in targets of different sizes. In one experiment they maintained sagittally symmetric postures; in the another they were required to rotate their entire body 180 degrees to complete the task. Measured peak push and pull hand forces ranged from 40 to 120 N and peak hand velocities ranged from 1.0 to 1.6 m/s in both studies. Psychophysical ratings were significantly correlated with peak push and pull hand forces but not peak velocity. Averages of peak hand force and velocity are used to develop some general recommendations for improved implementation of MHDs in industry.