Biomechanical assessment of lateral stiffness elements in the suspension system of a backpack

The purpose of this study was to examine the change in load distribution characteristics associated with adding lateral stiffness elements (rods) to a rucksack (backpack). A load distribution mannequin was instrumented with two 3D load cells to allow determination of the load applied to the shoulders and upper torso independent of the load applied to the hips and lower trunk. Position and mass of the payload (25 kg) were fixed at the centre of the volume of the rucksack and held constant during all testing. It was hypothesized that lateral rods would provide a force bridge that transfers part of the vertical load of the pack from the upper back and shoulders to the hip belt thereby reducing the vertical load on the torso, and possibly reducing the horizontal reaction force that produces a shear load on the spine. Results showed that these active stiffness elements shifted 14% of the vertical load from the upper torso to the pelvic region with lumbar shear load remaining relatively unchanged for all combinations of shoulder strap and waist belt tension. The lateral rods also provided a mean increase of 12% in the extensor moment at the L3-L4 level, thus reducing some demand on the erector spinae muscles.     

Development and assessment of the Canadian personal load carriage system using objective biomechanical measures

The Defence Research and Development Canada—Toronto managed a collaborative team of designers, biomechanists, ergonomists and military stakeholders in the development of a new personal load carriage (LC) system for the Canadian Forces. Ergonomics design principles using objective measurement tools and user-centred feedback from soldiers were considered essential to system development. The purpose of this study was to provide a detailed report of contributions by biomechanical testing to the final design of the final Canadian LC system. The Load Carriage Simulator and Compliance Tester were used to test design iterations of: three fragmentation vests, seven tactical vests and three iterations of the backpack. Test data were compared to a data pool of seventeen previously tested systems. Results indicated that the objective measures helped the design team by: (1) quantifying and understanding the consequences of various design changes; (2) predicting soldiers' responses to design changes in skin contact pressure, force and relative motion; (3) objectively comparing design iterations to other systems; and (4) providing information quickly so that ideas and recommendations could be incorporated into the next design iteration. It was concluded that objective assessments added valuable information not easily interpreted from human trials. However, objective assessments cannot replace human trials for feedback on functionality and features.     

A suite of objective biomechanical measurement tools for personal load carriage system assessment

For application to military and civilian needs, Defence Research and Development Canada—Toronto contracted Queen's University, Kingston to develop a suite of biomechanical assessment and analytical tools to supplement human-based load carriage system assessment methods. This suite of tools permitted efficient objective evaluation of biomechanical aspects of load-bearing webbing, vests, packs and their components, and therefore contributed to early system assessment and a rapid iterative design process. This paper is a summary of five assessment and analytical tools. A dynamic load carriage simulator was developed to simulate cadence of walking, jogging and running. The simulator comprised a computer-controlled pneumatic platform that oscillated anthropometrically weighted mannequins of varying dimensions from which measures of skin contact pressure, hip reaction forces and moments and relative pack-person displacements were taken. A stiffness tester for range of motion provided force-displacement data on pack suspension systems. A biomechanical model was used to determine forces and moments on the shoulders and hips, and validated using a static load distribution mannequin. Subjective perceptual rating systems were used gather soldier feedback during a standardized mobility circuit. Objective outcome measures were validated by means of other objective measures (e.g., Optotrak®, video, Instron®, etc.) and then compared to subjective ratings. This approach led to development of objective performance criteria for load carriage systems and to improvements in load carriage designs that could be used both in the military and in general.     

Thick shells of revolution: Derivation of the dynamic stiffness matrix of continuous elements and application to a tested cylinder

This paper describes a procedure for calculating the dynamic stiffness matrix of tubular shells with free edge boundary conditions. Such an analysis forms the basis for the Continuous Element Method. The method is used to formulate a thick axisymmetric shell element which takes into account rotatory inertia, transverse shear deformation and non-axisymmetric loadings.     

On the development of a computer-based handwriting assessment tool to objectively quantify handwriting proficiency in children

Standardized writing assessments such as the Minnesota Handwriting Assessment (MHA) can inform interventions for handwriting difficulties, which are prevalent among school-aged children. However, these tests usually involve the laborious task of subjectively rating the legibility of the written product, precluding their practical use in some clinical and educational settings. This study describes a portable computer-based handwriting assessment tool to objectively measure MHA quality scores and to detect handwriting difficulties in children. Several measures are proposed based on spatial, temporal, and grip force measurements obtained from a custom-built handwriting instrument. Thirty-five first and second grade students participated in the study, nine of whom exhibited handwriting difficulties. Students performed the MHA test and were subjectively scored based on speed and handwriting quality using five primitives: legibility, form, alignment, size, and space. Several spatial parameters are shown to correlate significantly (p < 0.001) with subjective scores obtained for alignment, size, space, and form. Grip force and temporal measures, in turn, serve as useful indicators of handwriting legibility and speed, respectively. Using only size and space parameters, promising discrimination between proficient and non-proficient handwriting can be achieved.