Measures of internal lumbar load in professional drivers – the use of a whole-body finite-element model for the evaluation of adverse health effects of multi-axis vibration

Abstract

In a re-analysis of an epidemiological study of professional drivers, a software tool available with standards DIN SPEC 45697:2012 and ISO/CD 2631–5:2014 Model 1 was used to calculate the risk to the lumbar spine in terms of daily compressive dose S(ed) and risk factor R. The tool was found to be suitable for risk assessment in a large cohort.

A prospective cohort study of low-back outcomes and alternative measures of cumulative external and internal vibration load on the lumbar spine of professional drivers

“…As aforementioned, this was done for purposes of comparison with the metrics for vibration shocks recommended by ISO 2631-5 (9). It should be noted, however, that the z-axis (vertical) weighted acceleration (a wz ) was the dominant directional component of vibration measured in all of the machines and vehicles (7,12). Considering the multiplying factor 1.4 for the horizontal axes according to EU Directive on mechanical vibration (5), only one vehicle during a special activity (wheel loader, stone transportation in a quarry) revealed a dominant directional component in the x-axis (7).…”

“…Some subjects operated a combination of two or three vehicles per working day, other subjects operated one machine exclusively. All of the time histories contained shocks in at least one direction according to several criteria for detecting shock (7). Impacts due to sitting down or losing the contact to the seat were eliminated.…”

“…These 80 model modifications delivered 17280 acceleration to spine-force transfer functions in total as a basis for calculating the force time histories (80 modifications of the model, 4 acceleration inputs (buttock, back, hands, feet), 3 acceleration directions, 6 spine levels, 3 spinal force directions). A description of the 4 observed sitting postures and the 10 BM/BMI categories, and the sophisticated procedure of data processing for the estimation of static and dynamic spinal forces based on FE models have been reported elsewhere (7).…”

“…The FE-models have been validated by means of experimental laboratory research on human biodynamics and field research on anthropometry and posture of representative groups of European drivers (10,(32)(33)(34). Present limitations of the FE-models concern its linearity, simplified modelling of soft tissue at the input areas, missing consideration of twisting, and limited verification for horizontal and rotational inputs (7). The current FE-models to calculate spinal forces during exposure to WBV do not provide a quantitative risk assessment for internal stresses caused by shear forces, bending and torsion, since reliable strength data (ultimate static strength, strength under dynamic repetitive load) for such stresses are not available.…”

“…or the vibration dose value according to a fourth power time-dependency (VDV in ms −1.75 ). A (8) and VDV are metrics of external vibration acceleration load and may be poorly correlated with the internal load acting on the lumbar spine (7). In particular, there is some evidence that the current metrics of WBV exposure might underestimate the severe health effects of vibration that contain shocks (8).…”