A systems-level perspective of the flexion-relaxation phenomenon in the lumbar spine

Standard anatomic classifications such as trunk , lower limbs , upper limbs can be misleading regarding the functional role and influence that the tissues in these body regions may play in adjacent body regions. In particular, much of the spine biomechanics literature has considered the lumbar spine in isolation, neglecting to account for the influence of the tissues of the lower extremities (muscles, ligaments and fascia) on the performance of the lumbar region of the torso. Some previous literature supports a systems level (i.e., trunk, pelvis and lower extremities) approach for better understanding of trunk stability during flexion-extension motions. The current study presents a new musculoskeletal model of the active spinal stability system that includes the local system (e.g., multifidus muscles) and global system (e.g., lateral erector spinae, rectus abdominis muscles etc.) as proposed by Bergmark (1989), but then adds a super global system that considers the influence of the lower extremity tissues on the responses of the lumbar region. This innovative model was verified throughout in vivo experiments involving human subjects that included three different physical exertion tasks that stressed the low back and the lower extremities in different ways to explore these important interactions. The empirical work in this dissertation focused on gathering data from the local, global and super global biomechanical systems before and after three 10 minute exercise protocols and then during a 40 minute recovery session. Twelve participants performed three separate experiments (three protocols) on different days: Protocol A- alternately perform 25 seconds of full trunk flexion and 5 seconds upright, relaxed posture; Protocol B- alternately perform 25 seconds of isometric exertion in a 45 degree trunk flexion posture and 5 seconds upright, relaxed posture; and Protocol C- consecutively perform 25 seconds of full trunk flexion followed by 5 seconds of upright, relaxed posture followed by 25 seconds of isometric exertion in a 45 degree trunk flexion posture and 5 seconds upright, relaxed posture. Kinematic and physiological measures were recorded before during after these protocols as well as during the recovery period. In addition, a variable describing the level of fixation of the pelvis was considered to allow for a direct evaluation of the role of the pelvis/lower extremities on the performance of the lumbar region during these exertions: 1) lower extremity restricted stooping posture (pelvis and thigh restriction) and 2) free stooping posture. The data collected in these experimental trials included the peak lumbar flexion angle, the peak hip flexion angle, the peak trunk flexion angle, the EMG-off angle (i.e., flexion-relaxation), and the average normalized integrated electromyography (NIEMG) for the agonist muscles (lumbar extensors (multifidus and iliocostalis)), the antagonist muscles (lumbar flexors (rectus abdominis and external obliques)) and the lower extremity synergistic muscles (gluteus maximus and biceps femoris). The results of in vivo experiments, focused on the role of the pelvis/lower extremities in trunk flexion-extension, showed a 6.4% greater lumbar flexion angle (36y vs. 38.3y), a 10.2% greater (or later) EMG-off angle in multifidus (31.6y vs. 34.8y), and a 8% greater EMG-off angle in the iliocostalis (30.6y vs. 33y) in the restricted stooping posture than in the free stooping posture. Collectively, these results suggest that additional passive moments about the lumbar spine are generated in the restricted stooping posture because of the relative fixation of the pelvis that is seen during the restricted stooping condition. Consistent with these results, 22% greater lower extremity activation (10.5% MVC vs. 8.2% MVC) was observed in the free stooping posture, as compared to the restricted stooping posture. This additional lower extremity muscle activation acts to stabilize the pelvis (the foundation of the spinal column) and generate passive moments in low back through the lumbodorsal fascia. Consequently, the enhanced pelvic stability and passive moments in the low back generated by the lower extremity active system (i.e. the super global system) led to the an 8% lower low back muscle activation level (15.1% MVC vs. 16. 3% MVC) in the free stooping condition. In addition, under the abnormal low back conditions (after protocols), the agonist muscles showed significant increases in both the free stooping posture and the restricted stooping posture (15% in both) to maintain spinal stability, but the synergist only increased in the free stooping (22%, 11.2% MVC vs. 13.7% MVC) (no difference in the restricted stooping posture). To summarize, these results indicate a significant role of the tissues of the larger super global system as a trunk stabilizer by immobilizing the pelvis during trunk flexion-extension motions and increasing the stiffness of the trunk systems by enhancing tension of the lumbodorsal fascia. Regarding the effects of the 10 minute protocols on the biomechanical responses, results showed greater full lumbar flexion and deeper biomechanical equilibrium point between passive tissues and external moment (i.e., EMG-off angles) than the baseline (initial measure) after Protocol A: full lumbar flexion increased 7%; EMG-off angle increased 7.2% in multifidus and increased 7.8% in iliocostalis. In Protocol B the trends in the dependent variables were opposite to those seen in Protocols A: full lumbar flexion angle decreased by 4% and the EMG-off angles decreased by 4.9% in the multifidus and by 6.3% in iliocostalis. Protocol C (the mixed protocol) generated similar, but less pronounced results as compared to Protocol A: full lumbar flexion increased by 3.7%; EMG-off angles increased by 3.7% in multifidus and by 5.9% in iliocostalis. The results of Protocol A and B are consistent with the results of previous studies of these responses and demonstrate important biomechanical effects that need to be considered when modeling the lumbar spine in full or near full-flexion postures. Protocol C was a condition that had not been considered in previous studies and these results indicate that the result of a mixed effort protocol may depend on the relative intensity of the passive vs. the active fatigue. In the current study the passive tissue fatigue appears to have dominated since the results of Protocol C are somewhat similar to those seen in Protocol A. In all three protocols there appears to have been significant compromise of the passive spinal stability system, as the muscle activities in agonist muscles and synergist muscles were significantly increased in all three protocols illustrating an increased need for active control of the lumbar region. In terms of the recovery process, the in vivo experiment, comparing characteristics of the recovery phase in three protocols, showed longer recovery time after the passive tissue elongation protocol (not fully recovered until 40 minutes of rest in all variables) than the muscle fatigue protocol (recovered after 5 minutes of resting in all variables) and the combined protocol (not fully recovered until 40 minutes of resting for the full lumbar flexion angle and the EMG-off angle; fully recovered in agonist muscle activation after 40 minutes of resting; and fully recovered in the synergist muscles after 5 minutes of resting). The results suggest that the slow recovery of the viscoelastic tissues caused by the prolonged stooping of Protocols A and C may lead to periods of spinal instability because of the abnormally lax passive tissues. While not a direct results of this study, these results may indicate an increased risk of injury during this period of passive tissue remodeling. Also, the enhanced activation in the synergist muscles (i.e., super global system) and depression in the antagonist muscles during the recovery session suggest an interaction mechanism between antagonist and synergist which may be planned in skilled motor programs before the initiation of the movement. Meanwhile, contrary to the results of passive tissues elongation protocol, the muscle fatigue protocol showed relatively quick recovery in all responses measures, but higher levels of muscle activity increase immediately after the protocol: Protocol B (agonist: 14.2%; synergist: 12.5%) vs. Protocol A (agonist: 9.2%; synergist: 4.7%) and Protocol C (agonist: 11.5%; synergist: 5.1%)). In all three protocols, the super global system (i.e., synergist) showed a recovery pattern that was quite similar to the agonist muscle response. The results of the theoretical modeling and experimental validation components of the current study indicate that a new musculoskeletal model with a more systems-level perspective is necessary to fully understand the biomechanical response of the lumbar spine during full flexion and near full flexion exertion. This study has filled a void in the literature in that it addresses 1) the role of the super global system (i.e., lower extremity) in both normal and abnormal condition, 2) the effect of combined effect protocol (both laxity of the passive tissues and fatigue of the active tissues), 3) differences in the biomechanical responses as a function of the type of fatigue developed (passive tissue, active tissue, combined passive and active tissue fatigue), and 4) dynamic and variable responses of the chosen biomechanical measures during recovery. The results of this new systems-level biomechanical model can be used to develop a new EMG-assisted model of spinal loading and spinal stability as well as guidelines for designing safer working environments that can lower the risks of musculoskeletal injury to the low back

A systems-level perspective of the biomechanics of the trunk flexion-extension movement: Part II – Fatigued low back conditions

Our companion paper demonstrated the importance of a systems-level perspective on spine biomechanics by showing the effects of lower extremity constraints during simple, trunk flexion-extension motions. This paper explores the impact of trunk muscle fatigue and stress-relaxation of lumbar passive tissues on this systems-level response. Twelve participants performed experimental protocols to achieve lumbar passive tissue stress-relaxation fatigue and lumbar muscle fatigue. Participants performed full range of sagittal-plane trunk flexion-extension under unconstrained stoop movement and pelvic/lower extremity constrained stoop movement. They performed these motions both before and after the fatigue protocols and trunk kinematics and muscle activities in trunk and lower extremity muscles were monitored. Under the condition of passive tissue fatigue, low back muscles and lower extremity muscles revealed significantly increased activation level (21% and 22%, respectively) in the free stoop condition but under the restricted stoop condition, there was no significant effect of the protocol. Under the lumbar muscle fatigue condition, a significant antagonistic and lower extremity activation effect (34% increase in abdominal muscles, 16% increase in lower extremity muscles) was observed in the free stooping condition while these variables were not affected by the protocol under the restricted stooping condition. Relevance to industry Fatigue of the lumbar musculature and passive tissues is prevalent in jobs requiring full trunk flexion postures. Developing accurate biomechanical models of spinal stress in these full stooping postures can help in the development of appropriate interventions to reduce the prevalence of back injuries in these jobs

A systems-level perspective of the biomechanics of the trunk flexion-extension movement: Part I – Normal low back condition

Most of the previous studies of the lumbar region have not considered the influence of pelvic and lower extremity characteristics on the performance of the lumbar region. The goal of the current study was to explore these more systems-level effects by assessing the effects of a pelvic/lower extremity constraint on the biomechanical response of the lumbar spine in an in-vivo experiment. Twelve participants performed full range of motion, sagittal-plane trunk flexion-extension movements under two conditions: unconstrained stoop movement and pelvic/lower extremity constrained stoop movement (six repetitions in each condition over three days). Kinematics and muscle activities of the trunk and lower extremity muscles were monitored. Results showed a significant effect of pelvic/lower-extremity constraint on a number of lumbar performance measures. Trunk flexion angle was, as expected, significantly reduced with the lower extremity constraints (81° (free stoop) vs. 56° (lower extremity constrained)). At a more local level, there was a 6.4% greater peak lumbar flexion angle and a 9.1% increase in the lumbar angle at which the trunk extensor musculature demonstrated flexion-relaxation in the constrained stooping condition as compared to the unconstrained stooping condition. Also, the EMG of the L3/L4 paraspinals was greater in the restricted stooping as compared to the free stooping (16.3% MVC vs. 15.1% MVC). Relevance to industry Low back injuries are a significant challenge to many industries and developing accurate models of spinal stress at full stooping postures can help in the development of appropriate interventions to reduce prevalence

Influence of asymmetry on the flexion relaxation response of the low back musculature

Background The flexion relaxation phenomenon has been extensively studied in sagittally symmetric postures. Knowledge about this phenomenon in asymmetric trunk postures is less well understood, and may help to reveal the underlying physiology of the passive tissue/active tissue load-sharing mechanism in the lumbar region. Methods Twelve participants performed fifteen controlled, full range trunk flexion–extension motions toward three asymmetric lifting postures (0° (sagittally symmetric), 15°, and 30° from the mid-sagittal plane). The electromyographic activity data from the paraspinals at the L3 and L4 levels and trunk kinematics data from motion sensors over the C7, T12 and S1 vertebrae were recorded. The lumbar flexion angles at which these muscles\u27 activities were reduced to resting levels during forward flexion provided quantitative data describing the effects of asymmetry on the passive tissue/active tissue interaction. Findings Flexion relaxation was observed in the muscles contralateral to the direction of the asymmetric trunk flexion motion. The response of the ipsilateral extensor musculature was much less consistent, with many trials indicating that flexion relaxation was never achieved. Increasing asymmetry from 0° to 30° led to a 10% reduction in the maximum lumbar flexion. Lumbar flexion angles necessary to achieve flexion relaxation in the contralateral muscles also decreased (L4 paraspinal-related angle decreasing by 15% and the L3 paraspinal-related angle decreasing by 21%). Interpretation Under asymmetric conditions the lumbar flexion angle at which the transition from active muscle to passive ligamentous extension moment is altered from that seen in symmetric motions and this transition can have implications for the loading of the spine in full flexion (or near full flexion) postures

The effects of horizontal load speed and lifting frequency on lifting technique and biomechanics

Lifting loads that have a horizontal velocity (e.g. lifting from a conveyor) is often seen in industry and it was hypothesised that the inertial characteristics of these loads may influence lifting technique and low back stress. Seventeen male participants were asked to perform lifting tasks under conditions of four horizontal load speeds (0 m/s, 0.7 m/s, 1.3 m/s and 2.4 m/s) and two lifting frequencies (10 and 20 lifts/min) while trunk motions and trunk muscle activation levels were monitored. Results revealed that increasing horizontal load speed from 0 m/s to 2.4 m/s resulted in an increase in peak sagittal angle (73° vs. 81°) but lower levels of peak sagittal plane angular acceleration (480°/s2 vs. 4°/s2) and peak transverse plane angular acceleration (200°/s per s vs. 140°/s per s) and a consistent increase in trunk muscle co-activation. Participants used the inertia of the load to reduce the peak dynamics of the lifting motion at a cost of increased trunk flexion and higher muscle activity

Digital Forensic Methodology for Detection of Abnormal Flight of Drones

When a drone accident has occurred, it is difficult to decide whether it is due to a crime, malfunction, mistake, or external force. Although the cause of the accident is elucidated through analysis of artifacts or flight data, there are many limitations. In this study, we present a method for detecting an abnormal flight using the motor current values and controller direction values of a drone. The experimental result revealed that, in the case of a normal flight, the current values of four motors were similar in hovering state and the current value of rear motors were increased when the drone was flying forwards. In the case of an abnormal flight, when the drone moved rightwards due to external force in hovering state, the current values of the two motors on the right side were increased greatly. After a period of time following the movement to the right side, the current values of all the motors converged to 0. In the future, motor current values and controller direction values may be used to determine whether an abnormal flight in a drone accident has occurred because of external force by wind, birds, persons, or the like

Nanoporous CuCo2O4 nanosheets as a highly efficient bifunctional electrode for supercapacitors and water oxidation catalysis

Efficient and low‐cost multifunctional electrodes play a key role in improving the performance of energy conversion and storage devices. In this study, ultrathin nanoporous CuCo2O4 nanosheets are synthesized on a nickel foam substrate using electrodeposition followed by air annealing. The CuCo2O4 nanosheet electrode exhibits a high specific capacitance of 1473 F g─1 at 1 A g─1 with a capacity retention of ∼93% after 5000 cycles in 3 M KOH solution. It also works well as an efficient oxygen evolution reaction electrocatalyst, demonstrating an overpotential of 260 mV at 20 mA cm─2 with a Tafel slope of ∼64 mV dec─1. in 1 M KOH solution, which is the lowest reported among other copper-cobalt based transition metal oxide catalysts. The catalyst is very stable at >20 mA cm─2 for more than 25 h. The superior electrochemical performance of the CuCo2O4 nanosheet electrode is due to the synergetic effect of the direct growth of 2D nanosheet structure and a large electrochemically active surface area associated with nanopores on the CuCo2O4 nanosheet surface