Muscle force evaluation and the role of posture in human lumbar spine under compression

Abstract

Using two nonlinear finite element models of the lumbar spine, the concept of optimal posture is explored by minimizing the segmental sagittal moments required for the equilibrium of the passive lumbar spine under a total of 2800 N axial compression while varying the pelvic tilt and lumbar lordosis. The redundant active-passive system is subsequently solved for this posture using a novel kinematics-based muscle calculation algorithm along with minimization approach. Some flattening in the lumbar spine substantially reduces the required moments and internal passive shear forces under 2800 N axial compression force. Small muscle forces are calculated for this optimal posture. The role of flattening in the lumbar lordosis and posterior pelvic tilt in diminishing the lumbar muscle activities in neutral postures is demonstrated. Without such changes in posture, the required moments probably exceed the moment-generating capability of local lumbar muscles. Consideration of such active-passive synergy and lack of its restriction may prove crucial in many activities. Moreover, a kinematics-based algorithm is proposed for the solution of spinal redundancy that fully accounts for the existing passive-active synergy while simultaneously satisfying all kinematics and equilibrium conditions along the length of the spine.

The lumbar spine has an intrinsic shape specific to each individual that remains a characteristic throughout flexion and extension

“…This might explain our findings such that the desired flexion posture was achievable largely through flexion in the upper lumbar levels with the lower lumbar spine remaining lordotic. The amount of curvature in the lumbar spine can affect the stresses and strains in the spine [8,14,36] and the distribution of curvature has been linked to some spinal pathologies [37]. Twin studies have reported a genetic influence on LBP occurrence [38,39] and with suggestions of postural familial associations it begs the question of whether intrinsic spinal shape might be genetically influenced and whether certain shapes might be more prone to LBP than others.…”

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

“…The beams modeled the overall nonlinear stiffness of T12-S1 motion segments (i.e., vertebrae, disc, facets and ligaments) at different directions and levels. The nonlinear load-displacement response under single and combined loads along with flexion versus extension differences were represented in this model based on numerical and measured results of previous single-and multi-motion segment studies [6,73,80,85,88,104]. The trunk mass and mass moments of inertia were assigned at gravity centers at different levels along the spine based on published data for trunk segments [77,78] and head/arms [105].…”

Role of intra-abdominal pressure in the unloading and stabilization of the human spine during static lifting tasks

“…The current study was set to delineate the role of IAP on muscle forces and spinal loads during regular static lifting activities involving standing and forward-flexed postures. The kinematics-based approach combined with a nonlinear finite-element model of spinal activepassive components was applied to estimate trunkmuscle forces, spinal loads, and stability [3,30,67]. This realistic nonlinear finite-element model circumvents many shortcomings in other biomechanical models by accounting for kinematics and kinetics conditions as well as passive-active synergies at all the spinal levels.…”

“…More details for both in vivo and finite-element model studies can be found elsewhere [3,30,67]. Kinematics of the spine under standing posture as well as trunk flexions of 40°and 65°with 180 N in hands were measured in fifteen healthy males (age 30±6 years, height 177±7 cm, mass 74±11 kg) using infrared light-emitted markers, LED, attached on the skin at the tip of T1, T5, T10, T12, L1, L3, L5, and S1 spinous processes.…”

“…1). The nonlinear load-displacement response under single and combined axial/shear forces and moments along with the flexion versus extension differences were represented in this model based on numerical and measured results of previous single-and multi-motion segment studies [59,60,66,67,75]. In all cases, based on the mean body weight of our subjects and percentage of body weight at each motion segment level reported elsewhere [62,70], a gravity load of 387 N was distributed eccentrically at different segmental levels.…”