Dynamic push and pull forces while using a manual material handling assist device

Movement assist devices are quickly replacing traditional manual methods of material handling. By providing these devices, ergonomists assume they are substantially reducing the musculo-skeletal strain associated with completing the task. Unfortunately, assist devices usually only minimize the gravitational force components of the task, and by their additional inertia, tend to increase dynamic manual requirements. The experiment reported here examines the dynamic force levels produced by inexperienced operators symmetrically pushing and pulling a small material handling assist device. Values are presented as a function of system and task parameters, such as load transported, movement distance, final placement accuracy and system friction. The results demonstrate that subjects performed the task using remarkably high push and pull forces. Experimental manipulations had only relatively small effects on the force levels observed. These results are discussed in terms of the ergonomic issues that may affect individual performance, training and device design.