The evaluation of a practical biomechanical model estimating lumbar moments in occupational activities

Abstract

To estimate the mechanical load on the low back in manual materials handling, the Static Strength Prediction Model (SSPM, University of Michigan) is widely used in the occupational field. It requires (for practical reasons) only a small number of input variables (five body segment angles, standing height, total body mass, external load on the hands) on which basis the moment at the lumbo-sacral intervertebral joint (beside other parameters) is computed. The dynamic character of the activities is ignored in the calculations. To evaluate the validity of the SSPM in various situations, lumbar moments in lifting/lowering activities at different lifting techniques and speeds obtained by the SSPM, were compared with those obtained by a more comprehensive dynamic model (DM). An analysis of variance showed significant effects (p = 0.001) of the biomechanical model applied and the lifting speed used on the peak lumbar moment values. No effects of lifting technique were found. The differences in results from the SSPM and DM were dependent on the lifting speed: the SSPM peak lumbar moments were on average 9% (not significant), 21% (significant at p = 0.005) and 42% (p = 0.0001) smaller compared to the DM moments in the slow (mean velocity in a complete lifting/lowering cycle, 0.2 m s-1), normal (0.4 m s-1) and fast (0.8 m s-1) speed condition respectively. The results indicate that the static/dynamic difference between the models is a major source for the different lumbar moments, while other differences between the SSPM and DM are of minor importance.

Supporting the upper body with the hand on the thigh reduces back loading during lifting

“…However, it has been shown previously that dynamic lifting results in higher forces compared to static or slow lifts (e.g., de Looze et al, 1994;Kingma et al, 2001;Lavender et al, 1999). Indeed, Gagnon et al (2011) reported peak L5S1 compression forces during unloaded dynamic full trunk flexion of 3107 when using a model requiring single-joint equilibrium and 3651N when using a model requiring multijoint equilibrium.…”

Analysis of squat and stoop dynamic liftings: muscle forces and internal spinal loads

“…It should be emphasized that the relative merits of these lifting techniques depend not only on the relative rotations at the thorax, pelvis and lumbar spine but also on other factors such as position of external loads, voluntary alterations in the lumbar curvature and speed of movement. These could partly be the reason why the literature remains yet inconclusive as some report smaller net moment and trunk load in squat lifting [13,43,58,83] while others indicate otherwise [23,28,57,59,98]. The reduction in net moment in squat lifts, under all cases with and without external load, is due primarily to smaller pelvic and lumbar (and hence thorax) rotations in this technique resulting in much reduced net moments from the mass of the upper body and the external load about the L5-S1 (Fig.…”

Foot positioning instruction, initial vertical load position and lifting technique: effects on low back loading

“…Knowledge about the effect of those determinants on low back loading could be used to develop effective preventive measures. For some determinants, like object weight (Davis and Marras 2000), lifting speed (Gagnon and Gagnon 1992, de Looze et al 1994, Kingma et al 2001, horizontal (Dolan et al 1994, Ferguson et al 2002 and vertical (Davis et al 1998, Ferguson et al 2002 position of the object relative to the worker, as well as several interactions between these factors (Lavender et al 2003), substantial evidence has been presented showing their influence on lumbar loading (de Looze et al 1994, Dolan et al 1994, Kingma et al 2001, Lavender et al 2003.…”