Describing the active region boundary of EMG-assisted biomechanical models of the low back

Abstract

Background: Electromyography-assisted (EMG-assisted) biomechanical models are used to characterize the muscle and joint reaction forces in the lumbar region. However, during a fullrange trunk flexion, there is a transition of extension moment from the trunk extensor muscles to the passive tissues of the low back, indicating that the empirical EMG data used to drive these EMG-assisted models becomes less correlated with the extensor moment. The objectives of this study were to establish the trunk flexion angles at which the passive tissues generate substantial trunk extension moment and to document how these angles change with asymmetry.Methods: Participants performed controlled trunk flexion-extension motions in three asymmetric postures. The trunk kinematics data and the electromyographic activity from L3-and L4-level paraspinals and rectus abdominis were captured. The time-dependent net internal active moment (from an EMG-assisted model) and the net external moment were calculated. The trunk and lumbar angles at which the net internal active moment was less than 70% of the external moment were found. Interpretation: These results indicate that EMG-assisted biomechanical models need to consider the role of passive tissues at trunk flexion angles significantly less than previously thought and these flexion angles vary as a function of the asymmetry and direction of motion.

Recovery Of Force Output And Electromyography From Trunk Muscles After Cyclic Passive Loading.

“…As the load on posterior lumbar tissues is increased the angle of trunk flexion also increases, whether statically or in repetitive cyclic movements (Dickey et al 2003;McGill & Brown1992). The increase in trunk flexion causes the lumbar tissues to become the dominant load bearers (Ning & Mirka, 2012). These repetitive loading schemes reduce the posterior viscoelastic tissue tension independent of muscular fatigue or external load applications (Olson).…”

Lumbar Posture and Tissue Loading During Short-Term Static Trunk Bending

“…During trunk bending, a transition of load from lumbar active muscles (e.g. lumbar extensor muscles) to lumbar passive tissues (ligaments, fascia discs, bone, and non-contractile component of muscles) occurs at deeper trunk flexion postures (Ning et al, 2011;Ning et al, 2012), which demonstrates the synergy between lumbar active muscles and passive tissues. Studies have suggested that this transition of load indicates that the tension generated by passive tissue stretching was adequate to counterbalance the external moment acting on the lumbar spine, therefore allowing lumbar extensor muscles to cease activation (Solomonow et al, 2003;Floyd and Silver, 1951;Allen, 1948).…”

“…the contractile component of muscles) and passive tissues (ligaments, fascia discs, bone, and non-contractile component of muscles). During forward trunk bending, a transition of load from lumbar active tissues to passive tissues occurs at deeper trunk flexion postures (Ning et al, 2011;Ning et al, 2012). This load shifting demonstrates the synergy between lumbar active and passive tissues and was termed as flexion relaxation phenomenon (FRP) by Silver (1951, 1955).…”

“…With the increase of lumbar and trunk flexion, the mechanical loadings on lumbar posterior ligamentous and discs increase (Adams and Dolan, 1996;Arjmand et al, 2011;McGill, 1997;Potvin et al, 1991;Kahrizi et al, 2007). In vivo studies have found an exponential increment in the bending moment resisted by lumbar passive tissues (spinal ligaments and discs) when the trunk is flexed more than half of the range between upright standing and full flexion (Adams and Dolan, 1991;Dolan et al, 1994b;Ning et al, 2012;Ning and Nussbaum, 2015). A number of previous studies have shown that the increase of lumbar and trunk flexion significantly increases spinal loading (Ning et al, 2012;Ning and Nussbaum 2015;Arjmand and Shirazi-Adl, 2006;Kahrizi et al, 2007), which was highly associated with the occurrence of LBP (Granata and Marras, 1993;Granata et al, 1997;Marras and Granata, 1995;Marras and Granata, 1997).…”

“…Flexion-Relaxation Phenomenon (FRP) was first discovered in the early 1950's (Floyd and Silver, 1951). During the past 30 years, FRP has been studied more intensively to investigate the load sharing mechanism between lumbar active and passive tissues (Kippers and Parker, 1984;Ning et al, 2011;Ning et al, 2012). FRP is identified by an observed reduction and eventual silence of the EMG signals of the lumbar extensor muscles during full trunk flexion motion ( Figure 4A).…”