Biomechanical Modelling and Objective Evaluation of a Dynamic Load Carriage Device

Abstract

The overall aim of this research project was to develop a methodology for the development and evaluation of an energy storage and return (ESAR) system, specifically dynamic rods (DR), for insertion into a typical backpack. The criteria for a successful ESAR were to reduce the relative pack vertical displacement at a delayed phase of the gait cycle thus reducing the force demands on the body. The first objective of this research project was to investigate the effectiveness of the DR across different loads and dynamic conditions. The approach involved the use of two types of load carriage evaluation tools: (1) a computational dynamic biomechanical model (DBM) and (2) a physical Load Carriage Simulator (LCS). The secondary objective was to examine the efficacy of this methodology and determine if the DR design concept met the ESAR criteria in both the DBM and LCS. The results demonstrated that, even though the DR had a marginal effect on the relative z-displacement of the pack and z-forces experienced at the waist and hips for the DBM, similar results were not observed in the LCS trials. There was also no phase shift of the backpack observed in either evaluation tool. This, along with the displacement and force data, suggested that the current DR design did not meet the criteria for an ESAR load carriage device. Finally, the comparison of key variables between the DBM and LCS demonstrated that the LCS could not be used to validate the DBM. Despite the limitations of this study, it has provided a starting point toward developing a standardized protocol for the design and development of novel load carriage systems. A supplemental study demonstrated that increased tension of the DR straps resulted in a reduction of shoulder strap forces because the DR acted as a bridge in the mechanical system, transferring some of the forces from the shoulders to the hip belt (pelvis). Therefore, this DR concept should be considered in the design of LC devices as the reduction of shoulder forces during load carriage is an area of concern.