Evaluation of Limiting Strength Constraints in a Comprehensive Biomechanical Model

Abstract

The strength constraints in a two-dimensional static human force exertion capability model (HFEC) have been evaluated using eight male and female subjects of varying anthropometry and strength capability. The model comprehensively estimates feasible exertion capability under symmetric conditions using a set of fifteen linear constraint equations from three constraint classes: strength, stability, and coefficient of friction (COF). This evaluation examines the nature of the limiting strength constraints. The computer model aided in designing tasks (combining posture with force exertion direction) that isolated upper extremity strength constraints and hip/torso strength constraints from stability and COF constraints. Subject performances of maximum exertions were recorded using force platforms and a multi-axis load cell to record external reaction forces at the hands and feet. Body posture was recorded with a 2D motion analysis system. The observed hand force exertions were compared to the exertions predicted by the model. The identity of the limiting constraints was well predicted by the model. The location of the constraints was logical and predictable. The results are discussed in the context of other modeling approaches as well as implications for future research. The HFEC approach shows excellent potential as an ergonomic engineering tool for teaching, evaluation, and design.