The Application of Whole-Body Musculoskeletal Modelling and Simulation to Estimate Lumbar Spinal Loading and Muscle Forces in Lifting Activities

Abstract

Lower back injury (LBI) commonly occurs in many workplaces during manual material handling tasks. Critical reviews indicate that compression force combined with axial rotation during lifting is highly associated with LBI. Moreover, although many existing biomechanical models have attempted to quantify lumbar spinal loading, many of them provide inaccurate results due to oversimplified representations of the musculoskeletal systems. Therefore, the purpose of this study was to apply a computer whole-body musculoskeletal modelling and simulation to estimate lumbar spinal loading at the L5/S1, L4/L5 and L3/L4 and the trunk muscle forces during vertical lifting (VL) and vertical lifting combined with a twisting movement (TL) of the spine. Thirteen healthy males lifted loads of 7 kg and 12 kg of two lifting types, VL and TL. For each lift, the movement of body segments and the ground reaction forces were recorded using an 8-camera Vicon system and two force plates, respectively. All the data were then analysed in OpenSim software (www.simtk.org) using the whole-body musculoskeletal model. The peak lateral shear forces at the L5/S1 and L4/L5 were significantly (p < 0.05) higher during TL than VL. Increased load (12 kg) resulted in significantly greater peak compression force, anterior shear force and lateral shear force than a 7 kg load at the L5/S1 and L4/L5. The peak force production of the psoas major, quadratus lumborum, multifidus, iliocostalis lumborum pars lumborum, longissimus thoracis pars lumborum, and external oblique were significantly higher during TL than VL. These muscle groups also produced greater peak force when lifting a 12 kg load than a 7 kg load. Additionally, asymmetrical muscle contractions were observed in these muscle groups, especially during TL. This study supports the notion that lifting a heavier load combined with a twisting movement may not be ideal due to excessive lumbar spinal loading, especially with a high lateral shear force at the L5/S1 and L4/L5. The great muscle force and asymmetrical muscle contractions during TL may also be related to the high occurrence of LBI within asymmetric lifting movements. Since the whole-body musculoskeletal modelling and simulation can reliably estimate lumbar spinal loading and the trunk muscles forces under all lifting conditions, this study may provide insight into their role during lifting tasks. The model may be applicable to future studies in many research disciplines involving dynamic movements.