Showing papers by "Jaap H. van Dieën published in 2000"

A review of biomechanical studies on stoop and squat lifting

Abstract: To assess the rationale of advocating the squat as opposed to the stoop technique, biomechanical studies comparing the two were reviewed. With the exception of some specific lifting tasks, net moments and compression forces were estimated to be equal or higher in squat lifting. Shear force and spinal bending moments appeared lower in squat lifting. Net moments and compression forces probably can cause injury, whereas the other load components remain below injury threshold. In conclusion, the literature does not provide support for advocating squat lifting.

Back Compressive and Shear Forces during Cart Pushing and Pulling

Abstract: Several epidemiological studies suggest that 9–18% of low back injuries are associated with pushing and pulling. Handle height and the direction of the exerted forces (pushing or pulling) are expected to be important determinants of the health risk. The objective of the present study was to investigate the effect of handle height during pushing and pulling on the peak net moments, peak compressive forces and peak shear forces at the L5-S1 level. Handle height was shown to effect low back loading during pushing and pulling.

2D Analysis of 3D Lifting: How Far can we Go?

Abstract: Occupational manual material handling (MMH) is generally not limited to the sagittal plane. Yet, for practical reasons, biomechanical modeling of low back loading during occupational MMH is mostly restricted to 2D. In this study, the limitations to such an approach are analyzed through quantification of the errors made during 2D analysis of 3D lifting. In addition, an estimate is given of the improvements that can be obtained using a simple method to resolve one major source of error, i.e. the error due to projection of lumbar markers onto the sagittal plane.

Occupational biomechanics of the low back

Abstract: Low back pain (LBP), the most prevalent and costly workrelated disorder, has often been associated with high or repetitive mechanical loading. In this respect it is not surprising that biomechanical modeling has a long-standing tradition in research related to the prevention of LBP. Theoretically one could think of several ways in which biomechanical modeling can contribute to the prevention of workrelated low-back pain. Biomechanical methods and models could be applied to: • evaluate alternative workplace layouts, working methods and techniques, • detect the most stressful tasks and task elements in a function, • set standards for workload and to compare MMH tasks against these standards, • increase understanding of how MMH can cause LBP. The multi-session symposium "Occupational Biomechanics of the Low Back" intends to present an overview of the possibilities and the limitations (validity and applicability) oflow back biomechanical modeling in ergonomics. Generally the first step in mechanical modeling of loads on the spine is aimed at obtaining an estimate of the net moment produced by all active muscles and stretched passive tissues crossing the lumbar spine. This estimate can be obtained through standard rigid body mechanics using a 'linked-segment model'. Kinetic, and kinematic measurements are combined with individual anthropometric data to calculate the forces and moments acting on the lumbosacral junction. Since the 1980's improved motion analysis systems greatly facilitated collection of kinematic data and consequently inverse dynamic models have become commonly used in the laboratory, both still only to a limited extent in the field. An introductory paper (Jager, et a1.)presents an overview of the possibilities and limitations of inverse dynamics in ergonomic field studies. This will be followed by papers focussing on common methodological problems in field applications and solutions to these problems. In view of limitations in data collection procedures several simplifying assumptions are commonly made in ergonomic studies. Two papers (Kingma, et a1.; Gagnon, et a1.) illustrate the errors these assumptions may cause and present solutions to reduce these. Finally, Baten et al. present a promising new approach to estimating low back moment in field studies. It has been argued that in order to gain more insight into injury mechanisms underlying work-related low back pain it is necessary to obtain estimates of forces acting on the spine and surrounding structures. The net moment provides a starting point for estimating these forces. Spinal forces are mainly determined by the muscle forces, which are in general much higher than the ligament forces and the gravitational force acting on the upper body and load. The estimation of muscle forces is unfortunately not straightforward. Since many muscles are spanning the lumbosarcal joint an infinite number of combinations of muscle forces can produce the same net moment. Several types of models, using for instance EMG based muscle force estimates, static optimization, or neural network technology, have been developed to tackle this problem The second session will focus on the validity of these approaches, which depend on the strategy for estimating load sharing between muscles (Perez, & Nussbaum), anatomical fidelity of the model (Marras, et al.) and assumptions regarding cocontraction (Dieen, et a1.). Biomechanical modeling can provide insight in spinalloads, which by comparison with in vitro strength data of spinal structures might even allow setting of standards with respect to load magnitude. However, this requires epidemiological verification, which may be hampered by the complexity of the biomechanical methods, precluding application in large-scale epidemiological studies, and by the nature of the suspected injury mechanisms. For example, complex or cumulative loading have been indicated by biomechanical experiments to be likely causes of injury, which can not be studied in epidemiological investigations very readily. However, recently epidemiological studies firmly based on biomechanical knowledge and expertise have been performed, which have verified the importance of task or subject characteristics which from a biomechanical perspective appear to constitute a risk. Three ofthe papers (Fathallah, et aI.; Norman, et aI.; Dolan, & Adams) will focus on this type of studies and their relationship to the underlying biomechanical experimentation and modeling. A fourth paper (Fraser and Potvin) will address the issue of unexpected loading a factor thusfar not studies extensively in epidemiology. Finally, in the fourth session applied ergonomic studies will be presented in which biomechanical low-back modeling was used to evaluate alternative designs (Kuijer, et a1.; Hoozemans, et a1.), to evaluate alternative working techniques (Dieen, et a1.), and to identify hazardous task elements requiring ergonomic redesign (Plamondon, et al.).

Effect of Center of Mass and Handle Location of Two-Wheeled Refuse Containers on Mechanical Loading

Abstract: The aim of the current study was to find out how the center of mass (COM) and handle location of a two-wheeled container affects handle forces and joint loading. Forces at the handles and joint loading were quantified in four subjects during steady, two-handed pushing and pulling of two-wheeled containers with nine different COM locations and eleven different handle locations. The COM location turned out to have a major influence on handle forces and joint loading, whereas the influence of the handle location was moderate. Subjects considerably adapted the tilt angle of the container in response to variations in handle location but hardly in response to variations in COM location. For two-handed pushing and pulling the current design of a two-wheeled container can be improved by moving the centre of mass of the loaded container in the direction of the axis of the wheels and by slightly increasing the height of the handles.

Effect of the number of two-wheeled containers at a gathering point on energetic workload and work efficiency

Abstract: The effect of the number of two-wheeled containers at a gathering point on the energetic workload and the work efficiency in refuse collecting was studied. The results showed that the size of the gathering point had no effect on the energetic workload. However, the size of the gathering point had an effect on the work efficiency. This study shows that an increase in work efficiency does not directly imply an increase in workload.