Retooling Jack’s Static Strength Prediction Tool

Often, ergonomists need to determine the maximum acceptable load or force for a given task. Ergonomic tools, like the NIOSH Lifting Guidelines (Waters et al, 1993) and the Liberty Mutual Tables (Snook & Ciriello, 1991)), provide such loads for selected population percentiles. In contrast, the UGS Jack Static Strength Prediction tool (JSSP), based on the University of Michigan’s 3D Static Strength Prediction Program (3DSSPP), uses force(s) as inputs and calculates the percentage of the male or female population that would be capable (%Cap) for a given task. Typically, the %Cap threshold will be a fixed number determined from corporate or government guidelines (e.g. 75% of females). Thus, in order to find the acceptable load, users of JSSP must iterate through loads until they find a %Cap that is just below their predetermined threshold. This paper details a new interface to the JSSP tool which, given the normal inputs plus the predetermined %Cap, will output the maximum acceptable force. It is expected that this interface will enhance the utility of the JSSP and allow for an easier determination of the optimal postures and acceptable forces for a particular task.