Are Stability and Instability Relevant Concepts for Back Pain?

Back-Health Knowledge and Misconceptions Related to the Daily Life Activities of Secondary School Students

High school students with better knowledge about back care have fewer problems, but conceptual errors can hinder the acquisition of essential knowledge necessary for developing healthy habits. This study analyzed secondary school students' declarative knowledge and misconceptions related to back care in daily activities. An exploratory cross-sectional study was conducted with 80 girls and 89 boys aged 14-18 years (M = 15.68, SD = 2.12). The Health Questionnaire on Back Care Knowledge in Activities of Daily Living was used to evaluate knowledge using the true answer model (TAM) and the misconception model (MM). Using the test-retest method, both models' reliability was confirmed (TAM = 0.75; MM = 0.77), while only a minimal measurement error was identified (TAM = -0.01; MM = -0.07). The average scores were 6.23 for the TAM and 2.29 for the MM. The results showed no significant differences in both models. The analysis indicated that students had the most accurate knowledge of the location and function of the spine, whereas misconceptions regarding anatomical understanding and body posture usage were common. An analysis of the results under Reassumption Theory emphasizes the significance of comprehending concepts such as load transmission and spinal stability to maintain back health, thus highlighting the need for improved education in these areas to address misconceptions and enhance overall back-care knowledge.

Muscle short-range stiffness behaves like a maxwell element, not a spring: Implications for joint stability

INTRODUCTION

Muscles play a critical role in supporting joints during activities of daily living, owing, in part, to the phenomenon of short-range stiffness. Briefly, when an active muscle is lengthened, bound cross-bridges are stretched, yielding forces greater than what is predicted from the force length relationship. For this reason, short-range stiffness has been proposed as an attractive mechanism for providing joint stability. However, there has yet to be a forward dynamic simulation employing a cross-bridge model, that demonstrates this stabilizing role. Therefore, the purpose of this investigation was to test whether Huxley-type muscle elements, which exhibit short-range stiffness, can stabilize a joint while at constant activation.

METHODS

We analyzed the stability of an inverted pendulum (moment of inertia: 2.7 kg m2) supported by Huxley-type muscle models that reproduce the short-range stiffness phenomenon. We calculated the muscle forces that would provide sufficient short-range stiffness to stabilize the system based in minimizing the potential energy. Simulations consisted of a 50 ms long, 5 Nm square-wave perturbation, with numerical simulations carried out in ArtiSynth.

RESULTS

Despite the initial analysis predicting shared activity of antagonist and agonist muscles to maintain stable equilibrium, the inverted pendulum model was not stable, and did not maintain an upright posture even with fully activated muscles.

DISCUSSION & CONCLUSION

Our simulations suggested that short-range stiffness cannot be solely responsible for joint stability, even for modest perturbations. We argue that short-range stiffness cannot achieve stability because its dynamics do not behave like a typical spring. Instead, an alternative conceptual model for short-range stiffness is that of a Maxwell element (spring and damper in series), which can be obtained as a first-order approximation to the Huxley model. We postulate that the damping that results from short-range stiffness slows down the mechanical response and allows the central nervous system time to react and stabilize the joint. We speculate that other mechanisms, like reflexes or residual force enhancement/depression, may also play a role in joint stability. Joint stability is due to a combination of factors, and further research is needed to fully understand this complex system.

The effect of chronic low back pain and lumbopelvic stabilization instructions on gluteus medius activation during sidelying hip movements

BACKGROUND

People with chronic low back pain (LBP) often demonstrate altered muscle activation with movements that involve the lumbopelvic region and hips.

OBJECTIVE

The purpose of this study was to compare gluteus medius activity during sidelying hip abduction (SHA) and sidelying hip abduction-lateral rotation (SHALR) with and without instruction for lumbopelvic stabilization in people with and without chronic LBP.

METHODS

A cross-sectional study was conducted recruiting participants with (n = 17) and without (n = 17) chronic LBP. Gluteus medius activity was recorded with surface electromyography during the performance of SHA and SHALR with and without instructions including the abdominal drawing-in maneuver for lumbopelvic stabilization.

RESULTS

For SHA and SHALR, there was a significant main effect for instruction for stabilization indicated by a decrease in gluteus medius activity with instructions (p = .001, p < .001). There was not a significant main effect of chronic LBP on gluteus medius activity between groups for either activity. There was no significant interaction effect of pain and instruction for stabilization with SHA or SHALR.

CONCLUSION

Knowledge of changes in gluteus medius muscle activation patterns with trunk stabilization instruction may help clinicians with assessment of exercise performance to optimize gluteus medius activation.

Attentional Distractions Do Not Influence Lumbar Spine Local Dynamic Stability during Repetitive Flexion-Extension Movements

The association between low back pain and lumbar spine local dynamic stability (LDS) appears to be modulated by if and how someone catastrophizes about pain, suggesting that the cognitive perceptions of pain may influence an individual's ability to control lumbar spine motion. Previous work also demonstrates that directing cognitive resources and attentional focus can influence movement performance. Therefore, we aimed to examine whether distracting attentional focus would influence lumbar spine LDS during repetitive flexion-extension movements. Sixteen participants performed repetitive spine flexion-extension movements under two baseline conditions (pre- and post-), and while attentional focus was distracted by either an external sensory stimulus or a cognitive-motor dual-task, both targeted at the hands. Lumbar spine LDS was examined over 30 continuous movement repetitions using maximum Lyapunov exponents. In comparison to both Baseline and Post-Baseline trials, the perceived mental workload was significantly elevated during the cognitive-motor dual-task trial but not the external sensory stimulus trial. The only statistically significant effect on LDS occurred in the Post-Baseline trial, where LDS was higher than in the cognitive-motor dual-task. In combination with previous work, these findings suggest that distracting attentional focus during repetitive lumbar spine flexion-extension movements does not have a negative influence on lumbar spine LDS.

The effect of the diaphragm stretching technique in the diaphragm contraction rate and trunk muscle activity in back pain patients

BACKGROUND

The diaphragm plays an important role in trunk stability. Therefore, diaphragmatic dysfunction is associated with low back pain.

OBSECTIVE

This study aimed to confirm the effectiveness of diaphragm stretching technique as a treatment method for low back pain by evaluating the diaphragm contraction rate, trunk muscle activity in patients with low back pain.

METHODS

Thirty-four patients with low back pain were randomly divided into two group: an experimental group and a control group. The diaphragm stretching technique was conducted in the experimental group and the placebo intervention was conducted in the control group. The diaphragm stretching technique was conducted once, maintaining the tension for 7 min. The placebo intervention was conducted in the same position as the diaphragm stretching technique but with only light contact maintained without pressure. The diaphragm contraction rate and trunk muscle activity were measured before and after the intervention, and the changes were compared and analyzed. A paired sample t-test was used to compare measurements before and after the intervention within the group. An independent t-test was used to compare the experimental and control group. Statistical significance (α) was set at 0.05.

RESULTS

In the experimental group, the diaphragm contraction rate increased significantly after the intervention. Trunk muscle activity decreased significantly (p< 0.05). However, all domains in the control group receiving the placebo intervention were not significantly different (p> 0.05). Comparative analysis of changes before and after the intervention between the groups showed significant differences in the diaphragm contraction rate and trunk muscle activity in the experimental group (p< 0.05).

CONCLUSION

The diaphragm stretching technique improved the diaphragm contraction rate and trunk muscle activity was lower due to the improved trunk stabilization function of the diaphragm. Therefore, the diaphragm stretching technique can be recommended as a physical therapy intervention to improve pain in patients with low back pain.

Comparative evaluation of different spinal stability metrics

Direct in vivo measurements of spinal stability are not possible, leaving computational estimations (such as dynamic time series and structural analyses) as the feasible option. However, differences between different stability assessment approaches and metrics remain unclear. To explore this, we asked 32 participants to perform 35 cycles of repetitive lifts with and without load (4/2.6 kg for males/females). EMG signals and 3D kinematics were collected via 12 surface electrodes and 17 inertial sensors, and three dynamical stability measures were computed: short and long temporal and conventional maximum Lyapunov exponents (LyE) and maximum Floquet multipliers (FM). A dynamic subject-specific EMG-assisted musculoskeletal model computed four structural stability measures (critical muscle stiffness coefficient at which spine becomes unstable, average spine stiffness, minimum and geometric average of Hessian matrix eigenvalues). Across cycles, dynamical and structural stability outcomes varied noticeably. Temporal short-term LyE and all structural stability measures were more influenced by the cycle percentage (posture factor) than by phase (lifting, lowering) or load factor. The effect of all factors were non-significant for FM and long LyE, except for the posture on LyE-L with a small effect size. Pearson's correlations revealed a weak to moderate, or non-existent, correlation between structural and dynamical stability metrics, with small shared variances, underscoring their distinct and independent nature and theoretical foundations. Moreover, the low sensitivity of dynamic measures to posture and load factors, found in this study, calls for further examination. Considering the limitations and shortcomings of both dynamical and structural stability assessment approaches, there is a need for the development of improved musculoskeletal stability evaluation techniques.

Numerical investigation of intra-abdominal pressure and spinal load-sharing upon the application of an abdominal belt

Chronic low back pain patients may experience spinal instability. Abdominal belts (ABs) have been shown to improve spine stability, trunk stiffness, and resiliency to spinal perturbations. However, research on the contributing mechanisms is inconclusive. ABs may increase intra-abdominal pressure (IAP) and reduce paraspinal soft tissue contribution to spine stability without increasing spinal compressive loads. A finite element model (FEM) of the spine inclusive of the T1-S1 vertebrae, intervertebral discs (IVDs), ribcage, pelvis, soft tissues, and abdominal cavity, without active muscle forces was developed. An identical FEM with an AB was developed. Both FEMs underwent trunk flexion. Following validation, the models' intervertebral rotation (IVR), IAP, IVD pressure, and tensile stress in the multifidus (MF), erector spinae (ES), and thoracolumbar fascia (TLF) were compared. The inclusion of an AB resulted in a 3.8 kPa IAP increase, but a decreased average soft tissue tensile stress of 0.28 kPa. The TLF withstood the majority of tension being transferred across the paraspinal soft tissues (>70 %). The average IVR in the AB model decreased by 10 %, with the lumbar spine experiencing the largest reduction. The lumbar IVDs of the AB model likewise showed a 31 % reduction in average IVD pressure. Using an AB improved trunk bending stiffness, primarily in the lumbar spine. Wearing an AB had minimal effect on reducing tensile stress in theES. The skewed stress distribution towards the TLF suggests its large contribution to spine stability and the potential advantage in unloading the structure when wearing an AB, measured herein at8 %.

Impaired Lumbar Extensor Force Control Is Associated with Increased Lifting Knee Velocity in People with Chronic Low-Back Pain

The ability of the lumbar extensor muscles to accurately control static and dynamic forces is important during daily activities such as lifting. Lumbar extensor force control is impaired in low-back pain patients and may therefore explain the variances in lifting kinematics. Thirty-three chronic low-back pain participants were instructed to lift weight using a self-selected technique. Participants also performed an isometric lumbar extension task where they increased and decreased their lumbar extensor force output to match a variable target force within 20-50% lumbar extensor maximal voluntary contraction. Lifting trunk and lower limb range of motion and angular velocity variables derived from phase plane analysis in all planes were calculated. Lumbar extensor force control was analyzed by calculating the Root-Mean-Square Error (RMSE) between the participants' force and the target force during the increasing (RMSEA), decreasing (RMSED) force portions and for the overall force error (RMSET) of the test. The relationship between lifting kinematics and RMSE variables was analyzed using multiple linear regression. Knee angular velocity in the sagittal and coronal planes were positively associated with RMSEA (R2 = 0.10, β = 0.35, p = 0.046 and R2 = 0.21, β = 0.48, p = 0.004, respectively). Impaired lumbar extensor force control is associated with increased multiplanar knee movement velocity during lifting. The study findings suggest a potential relationship between lumbar and lower limb neuromuscular function in people with chronic low-back pain.

Muscle-driven forward dynamic active hybrid model of the lumbosacral spine: combined FEM and multibody simulation

Most spine models belong to either the musculoskeletal multibody (MB) or finite element (FE) method. Recently, coupling of MB and FE models has increasingly been used to combine advantages of both methods. Active hybrid FE-MB models, still rarely used in spine research, avoid the interface and convergence problems associated with model coupling. They provide the inherent ability to account for the full interplay of passive and active mechanisms for spinal stability. In this paper, we developed and validated a novel muscle-driven forward dynamic active hybrid FE-MB model of the lumbosacral spine (LSS) in ArtiSynth to simultaneously calculate muscle activation patterns, vertebral movements, and internal mechanical loads. The model consisted of the rigid vertebrae L1-S1 interconnected with hyperelastic fiber-reinforced FE intervertebral discs, ligaments, facet joints, and force actuators representing the muscles. Morphological muscle data were implemented via a semi-automated registration procedure. Four auxiliary bodies were utilized to describe non-linear muscle paths by wrapping and attaching the anterior abdominal muscles. This included an abdominal plate whose kinematics was optimized using motion capture data from upper body movements. Intra-abdominal pressure was calculated from the forces of the abdominal muscles compressing the abdominal cavity. For the muscle-driven approach, forward dynamics assisted data tracking was used to predict muscle activation patterns that generate spinal postures and balance the spine without prescribing accurate spinal kinematics. During calibration, the maximum specific muscle tension and spinal rhythms resulting from the model dynamics were evaluated. To validate the model, load cases were simulated from -10° extension to +30° flexion with weights up to 20 kg in both hands. The biomechanical model responses were compared with in vivo literature data of intradiscal pressures, intra-abdominal pressures, and muscle activities. The results demonstrated high agreement with this data and highlight the advantages of active hybrid modeling for the LSS. Overall, this new self-contained tool provides a robust and efficient estimation of LSS biomechanical responses under in vivo similar loads, for example, to improve pain treatment by spinal stabilization therapies.

Effect of Instability Training on Compensatory Muscle Activation during Perturbation Challenge in Young Adults

Balance requires constant adjustments in muscle activation to attain force steadiness. Creating appropriate training can be challenging. The purpose of this study was to examine the effects of 2 weeks of front squat instability training using a water-filled training tube on force steadiness during an instability challenge. Control (CON, n = 13) and experimental (EXP, n = 17) subjects completed pre- and post-testing for EMG variability by completing one set of 10 repetitions with a stable and unstable training tube. Electrodes were placed bilaterally on the anterior deltoid, paraspinal, and vastus lateralis muscles. CON subjects completed 2 weeks of training using a stable training tube, while EXP subjects trained with a water-filled instability tube. EMG data were integrated for each contraction, and force steadiness was computed using the natural log of coefficient of variation. CON results showed no changes in force steadiness for any condition. EXP showed significant reductions in EMG activation variability across all muscles. These results indicate a significant training effect in reducing muscle activation variability in subjects training with a water-filled instability training device. Improvements seen in these healthy subjects support the development of training implements for a more clinical population to help improve force steadiness.

Delayed response in rectus abdominis muscle following a step perturbation in subjects with and without recurrent low back pain

BACKGROUND

Delayed trunk and lower limb muscle activation is associated with balance loss and fall injuries in subjects with recurrent low back pain (LBP).

PURPOSE

This study was conducted to compare differences in the onset of muscle contractions of the trunk and lower limb muscles following a treadmill-induced step perturbation between subjects with and without LBP.

METHODS

Eighty-three right limb dominant individuals (43 subjects with LBP and 40 control subjects) were exposed to the perturbation (0.31 m/s velocity for 0.2 m). The electromyography (EMG) reaction times were analyzed during the first step following the perturbation. The EMG electrodes were placed on both sides of the trunk and lower limbs, including the rectus abdominis (RA), erector spinae (ES), tibialis anterior (TA), and gastrocnemius (GA) muscles.

RESULTS

The group x muscle interaction was statistically significant (F = 9.44, p = 0.003). The TA muscle activation was significantly delayed compared to the RA, ES, and GA. There was a significant interaction on side x muscle (F = 4.14, p = 0.04). The RA muscles were significantly delayed on the non-dominant (t = - 3.35, p = 0.001) and dominant (t = - 2.53, p = 0.01) sides in the LBP group.

CONCLUSION

The LBP group demonstrated a delayed reaction time on the RA muscles, which indicated poor trunk control relative to the lower limbs. The delayed bilateral RA muscle might indicate possible coordination problems relative to the ES and lower limb muscles, which may lead to potential fall hazards.

Evaluation of the degeneration of the multifidus and erector spinae muscles in patients with low back pain and healthy individuals

BACKGROUND

Although several studies have been conducted to determine the cause of low back pain (LBP), a sufficient correlation has not been found between research findings and symptoms. Therefore there seems to be a need for studies to explain the relationship between pain and morphological changes in the paraspinal muscles of patients with LBP through comparisons with healthy control subjects.

OBJECTIVE

The aim of this study was to examine degeneration in the lumbar musculus multifidus (LMF) and lumbar musculus erector spinae (LES) muscles in patients with chronic LBP with non-radiculopathy lumbar disc herniation (LDH), patients with mechanical LBP, and healthy individuals.

METHODS

The study included 35 patients with mechanical LBP, 38 patients with non-radiculopathy LDH, and a control group of 36 healthy participants. In all patients and the control group, evaluations were made on axial magnetic resonance imaging slices at L3-S1 level of the LMF and LES cross-sectional areas (CSA), total CSA (TCSA = LMF+LES), fat infiltrations and asymmetries.

RESULTS

The mean CSA values of the right and left LMF and LES showed significant differences between the groups (p< 0.001, p= 0.002, p= 0.002, p= 0.010, respectively). Fat infiltrations showed a difference between the right-left LMF and left LES groups (p= 0.007, p< 0.001, p= 0.026, respectively). Asymmetry was not observed between the CSA and TCSA of the right and left sides.

CONCLUSION

A correlation was found between fat infiltration in the LMF and mechanical LBP and LDH. However, no significant correlation was determined between LBP and the CSA and TCSA of the LMF and LES. This was thought to be due to an incorrect result of CSA and TCSA in the evaluation of muscle mass. Therefore, for a more accurate evaluation of muscle mass, it can be considered necessary to measure muscle atrophy associated with fat infiltration or functional CSA.

The interactions between agonist-to-antagonist muscle strength performance and plantar pressure distribution, foot contact area, and impulse in novice ballet dancers

BACKGROUND

Hip, trunk, knee, and ankle/foot muscles may lead to increased variability in the components of balance and plantar pressure distribution (PPD) analysis. However, the role of these muscle groups in the PPD of different ballet techniques in novice ballet dancers has not previously been studied.

OBJECTIVE

Our objective was to examine whether balance and PPD vary among five different ballet techniques and correlate with the agonist-to-antagonist strength performance of trunk, knee, hip, and ankle muscles in adolescent ballet dancers.

METHODS

The anthropometric parameters, muscle strength performance, balance, and PPD of sixty healthy female ballet dancers (age: 14.36 ± 2.18 y) were measured at 48-h intervals.

RESULTS

The forefoot's PPD was significantly greater than the midfoot and rearfoot for all techniques (p= 0.000). The percent plantar load of forefoot during développé à la seconde (side, front, back), passé, and penché was greater than midfoot (166.56%, 161.51%, 168.11%, 165.14%, 174.04%) and rearfoot (47.75%, 32.84%, 43.83%, 48.73%, 49.66) for all techniques, respectively. The forefoot's PPD, impulse, and contact area during all techniques were significantly correlated with the trunk muscle strength ratio (p< 0.05).

CONCLUSION

Ballet dancers with higher trunk muscle strength imbalance showed a greater percentage difference in pressure load between the left and right foot in the anterior and posterior directions, poor balance, aggravated trunk imbalance, increased PPD, contact area, and impulse in the forefoot during each technique.

Differences in trunk and lower extremity muscle activity during squatting exercise with and without hammer swing

Perturbation exercises enhance lower limb and trunk muscles, and adding swing perturbation while loading during exercise might improve muscle activation or strength. This study aimed to check variations in trunk and lower limb muscle activity during conventional isometric squats, and whether it will change with or without swing using the Hammerobics-synchronized squat method. Twelve healthy men participated in this study. Activities for the abductor hallucis, tibialis anterior, tibialis posterior, peroneus longus, rectus femoris, biceps femoris long head, semitendinosus, gluteus maximus, multifidus, and internal oblique muscles were measured using surface electromyography during a Hammerobics-synchronized squat and conventional isometric squat. Muscle activities were statistically compared between squat methods. Hammerobics-synchronized squats significantly activated the abductor hallucis, tibialis anterior, tibialis posterior, peroneus longus, semitendinosus, and multifidus muscles, in both phases, compared with the conventional isometric squats. The Hammerobics-synchronized squat exercise can be considered for trunk and foot stability exercise.

The Efficacy of Lumbar Support on Pain, Disability, and Motor Control in Women With Postpartum Pelvic Girdle Pain: Protocol for a Randomized Controlled Trial

BACKGROUND

Pregnancy-related posterior pelvic girdle pain (PPGP) is one of the most important clinical manifestations of postpartum back pain. Those affected often complain of discomfort during daily activities. It is hypothesized that altered motor control is associated with perceived pain. Pelvic support can regulate possible underlying altered motor control mechanisms and decrease pain. However, the influence of a lumbosacral orthosis, which is broader support that allows for a wider contact area and more skin sensory stimulation to restore proper motor function, has not yet been investigated in women with postpartum PPGP.

OBJECTIVE

This study investigates the efficacy of broader lumbar support and narrower pelvic support on pain, proprioception, disability, and muscle strength in women with pregnancy-related PPGP.

METHODS

This study will be a single-center, 3-armed, participant-blinded, randomized controlled trial. In total, 84 women diagnosed with pregnancy-related PPGP will be recruited and randomly assigned into 3 groups. Intervention groups A and B will receive pelvic and lumbar supports, respectively. Group C (control) will receive only a patient education leaflet containing advice on strengthening exercises, comfortable positions, and other practical information. The study outcomes are pain, effort score during the active straight leg raising test, maximum isometric hip flexion force, maximum isometric hip external rotation force, maximum isometric trunk rotation force, and joint position reproduction of hip abduction. The study outcomes will be measured at 4 time points: baseline (T1), immediately after the intervention (T2), 4 weeks following interventions began (at this time, the intervention period is completed) (T3), and 1 week after discontinuing the interventions (T4) to evaluate the possible lasting effects of wearing supports. Multivariate analysis of variance will be used to test between- and within-group differences.

RESULTS

Recruitment for this study will be started in summer 2022 and is expected to be completed by the end of fall 2022.

CONCLUSIONS

This study will examine the efficacy of broader lumbar support as an early rehabilitative treatment for women receiving postpartum posterior pelvic pain support compared to those receiving a narrower pelvic support. We expect the broader lumbar support to impact pain management and disability better than the current narrower pelvic belt. Long-term follow-up studies will help determine whether such lumbosacral orthosis reduces pain and improves daily activities in women with pregnancy-related PPGP.

TRIAL REGISTRATION

Iranian Registry of Clinical Trials IRCT20150210021034N11; https://www.irct.ir/trial/54808.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

PRR1-10.2196/40553.

Perturbation-based trunk stabilization training in elite rowers: A pilot study

Introduction

Low back pain is a major health issue in elite rowers. High training volume, frequent flexion movements of the lower spine and rotational movement in sweep rowing contribute to increased spinal strain and neuropathological patterns. Perturbation-based trunk stabilization training (PTT) may be effective to treat neuromuscular deficits and low back pain.

Methods

All boat classes (8+, 4+/-, 2-) of the male German national sweep rowing team participated in this non-randomized parallel group study. We included 26 athletes (PTT: n = 12, control group: n = 14) in our analysis. Physical and Sports therapists conducted 16 individualized PTT sessions á 30–40 minutes in 10 weeks, while the control group kept the usual routines. We collected data before and after intervention on back pain intensity and disability, maximum isometric trunk extension and flexion, jump height and postural sway of single-leg stance.

Results

We found less disability (5.3 points, 95% CI [0.4, 10.1], g = 0.42) for PTT compared to control. Pain intensity decreased similar in both groups (-14.4 and -15.4 points), yielding an inconclusive between-group effect (95% CI [-16.3, 14.3]). Postural sway, strength and jump height tend to have no between- and within-group effects.

Conclusion

Perturbation-based trunk stabilization training is possibly effective to improve the physical function of the lower back in elite rowers.

Evaluating stability of human spine in static tasks: a combined in vivo-computational study

Various interpretations and parameters have been proposed to assess spinal stability such as antagonist muscle coactivity, trunk stiffness and spinal buckling load; however, the correlation between these parameters remains unknown. We evaluated spinal stability during different tasks while changing the external moment and load height and investigated likely relationships between different EMG- and model-based parameters (e.g., EMG coactivity ratio, trunk stiffness, force coactivity ratio) and stability margins. EMG and kinematics of 40 young healthy subjects were recorded during various quasi-static tasks. Muscle forces, trunk stiffness and stability margins were calculated by a nonlinear subject-specific EMG-assisted-optimization musculoskeletal model of the trunk. The load elevation and external moment increased muscle activities and trunk stiffness while all stability margins (i.e., buckling loads) decreased. The force coactivity ratio was strongly correlated with the hand-load stability margin (i.e., additional weight in hands to initiate instability; R² = 0.54) demonstrating the stabilizing role of abdominal muscles. The total trunk stiffness (Pearson's r = 0.96) and the sum of EMGs of back muscles (Pearson's r = 0.65) contributed the most to the T1 stability margin (i.e., additional required load at T1 for instability/buckling). Force coactivity ratio and trunk stiffness can be used as alternative spinal stability metrics.

Recovery of the lumbopelvic movement and muscle recruitment patterns using motor control exercise program in people with chronic nonspecific low back pain: A prospective study

This study aims to investigate the dysfunction and recovery of the lumbopelvic movement and motor control of people with chronic nonspecific low back pain after a structured rehabilitation which emphasizes on re-education and training of movement and motor control. The lumbopelvic movement and motor control pattern of 30 adults (15 with chronic low back pain, 15 healthy controls) were assessed using 3D motion and electromyographic analysis during the repeated forward bending test, in additional to the clinical outcome measures. Regional kinematics and muscle recruitment pattern of the symptomatic group was analysed before and after the 6-week rehabilitation, and compared to healthy controls. Significant improvement in back pain, functional capacity and self-efficacy of the symptomatic group was found after the rehabilitation. Patients with chronic nonspecific low back pain were capable to recover to a comparable level of the healthy controls in terms of their lumbopelvic movement and motor control pattern upon completion of a 6-week rehabilitation program, despite their dysfunction displayed at baseline. Phase specific motor control reorganization in which more profound and positive changes shown during the flexion phase. Our findings indicate that the recovery of the movement and motor control pattern in patients with chronic low back pain achieved to a comparable level of the healthy able-bodies. The improvement of both the physical outcome measures suggest that specific rehabilitation program which emphasizes on optimizing motor control during movements would help promoting the functional recovery of this specific low back pain subgroup.

Calibration and validation of a novel hybrid model of the lumbosacral spine in ArtiSynth-The passive structures

In computational biomechanics, two separate types of models have been used predominantly to enhance the understanding of the mechanisms of action of the lumbosacral spine (LSS): Finite element (FE) and musculoskeletal multibody (MB) models. To combine advantages of both models, hybrid FE-MB models are an increasingly used alternative. The aim of this paper is to develop, calibrate, and validate a novel passive hybrid FE-MB open-access simulation model of a ligamentous LSS using ArtiSynth. Based on anatomical data from the Male Visible Human Project, the LSS model is constructed from the L1-S1 rigid vertebrae interconnected with hyperelastic fiber-reinforced FE intervertebral discs, ligaments, and facet joints. A mesh convergence study, sensitivity analyses, and systematic calibration were conducted with the hybrid functional spinal unit (FSU) L4/5. The predicted mechanical responses of the FSU L4/5, the lumbar spine (L1-L5), and the LSS were validated against literature data from in vivo and in vitro measurements and in silico models. Spinal mechanical responses considered when loaded with pure moments and combined loading modes were total and intervertebral range of motions, instantaneous axes and centers of rotation, facet joint contact forces, intradiscal pressures, disc bulges, and stiffnesses. Undesirable correlations with the FE mesh were minimized, the number of crisscrossed collagen fiber rings was reduced to five, and the individual influences of specific anatomical structures were adjusted to in vitro range of motions. Including intervertebral motion couplings for axial rotation and nonlinear stiffening under increasing axial compression, the predicted kinematic and structural mechanics responses were consistent with the comparative data. The results demonstrate that the hybrid simulation model is robust and efficient in reproducing valid mechanical responses to provide a starting point for upcoming optimizations and extensions, such as with active skeletal muscles.

Abdominal Expansion versus Abdominal Drawing-In Strategy on Thickness and Electromyography of Lumbar Stabilizers in People with Nonspecific Low Back Pain: A Cross-Sectional Study

The abdominal expansion (AE) strategy, involving eccentric contraction of the abdominal muscles, has been increasingly used in clinical practices; however, its effects have not been rigorously investigated. This study aimed to investigate the immediate effects of the AE versus abdominal drawing-in (AD) strategy on lumbar stabilization muscles in people with nonspecific low back pain (LBP). Thirty adults with nonspecific LBP performed the AE, AD, and natural breathing (NB) strategies in three different body positions. Ultrasonography and surface electromyography (EMG) were, respectively, used to measure the thickness and activity of the lumbar multifidus and lateral abdominal wall muscles. The AE and AD strategies showed similar effects, producing higher EMG activity in the lumbar multifidus and lateral abdominal wall muscles when compared with the NB strategy. All muscles showed higher EMG activity in the quiet and single leg standing positions than in the lying position. Although the AE and AD strategies had similar effects on the thickness change of the lumbar multifidus muscle, the results of thickness changes of the lateral abdominal muscles were relatively inconsistent. The AE strategy may be used as an alternative method to facilitate co-contraction of lumbar stabilization muscles and improve spinal stability in people with nonspecific LBP.

A systematic review of movement and muscular activity biomarkers to discriminate non-specific chronic low back pain patients from an asymptomatic population

The identification of relevant and valid biomarkers to distinguish patients with non-specific chronic low back pain (NSCLBP) from an asymptomatic population in terms of musculoskeletal factors could contribute to patient follow-up and to evaluate therapeutic strategies. Several parameters related to movement and/or muscular activity impairments have been proposed in the literature in that respect. In this article, we propose a systematic and comprehensive review of these parameters (i.e. potential biomarkers) and related measurement properties. This systematic review (PROSPERO registration number: CRD42020144877) was conducted in Medline, Embase, and Web of Knowledge databases until July 2019. In the included studies, all movements or muscular activity parameters having demonstrated at least a moderate level of construct validity were defined as biomarkers, and their measurement properties were assessed. In total, 92 studies were included. This allowed to identify 121 movement and 150 muscular activity biomarkers. An extensive measurement properties assessment was found in 31 movement and 14 muscular activity biomarkers. On the whole, these biomarkers support the primary biomechanical concepts proposed for low back pain. However, a consensus concerning a robust and standardised biomechanical approach to assess low back pain is needed.

The immediate effect of two lumbar stabilization methods on postural control parameters and their reliability during two balance tasks

Background: Lumbosacral orthosis (LSO) and/or the isolated contraction of the transversus abdominis muscle by the abdominal drawing-in maneuver (ADIM) can increase lumbar stiffness, consequently influencing postural control. The purpose of this study was to compare the effects of LSO and ADIM on postural control during two balance tasks and determine their reliability.Methods: Twenty participants (50% men) randomly performed three experimental conditions: 1) without lumbar stabilization, 2) with LSO), and 3) with ADIM. Each experimental condition was tested in two postural tasks: semi-tandem and one-legged stance on a force platform for 30 seconds, while the Center of pressure postural (COP) parameters were computed.Results: The two methods of lumbar stabilization were comparable and did not significantly reduce the COP values across time, even though a few individuals presented a change in their COP data above the levels of measurement errors. The reliability of these measurements was generally acceptable and sometimes excellent (≥ 0.90 and ≤10% error measurement).Conclusions: Both LSO and isolated contraction of the transversus abdominis muscle by ADIM do not change postural control in one-legged stance and in semi-tandem tasks. These results have implications for use or not these methods for postural control on a rehabilitation perspective.

Low-Back Pain and Knee Position-Related Differences on Postural Control Measures During a One-Legged Stance in Athletes

CONTEXT

Chronic low-back pain (CLBP) may be associated with changes in postural balance in athletes as poor postural control during sports practice.

OBJECTIVE

To compare the postural control of athletes with and without CLBP during 2 one-legged stance tasks and identify the center of pressure (COP) cutoff values to determine the main differences. Designed: A cross-sectional study.

SETTING

Laboratory of functional evaluation and human motor performance.

PARTICIPANTS

A total of 56 male athletes, 28 with and 28 without CLBP (mean age = 26 y).

INTERVENTION

The one-legged stance with knee extension and with the knee at 30° flexion tasks were measured and analyzed on a force platform. The participants completed three 30-second trials (30 s of rest between each trial).

MAIN OUTCOME MEASURES

The COP parameters: the area of COP, mean COP sway velocity in both the anteroposterior and mediolateral directions, and total COP displacement were computed, and a receiver operating characteristics curve analysis was applied to determine the group differences.

RESULTS

Athletes with CLBP had poorer postural control (P < .01) in both tasks. The 30° knee flexion reported more postural instability than the knee extension for all COP parameters (a large effect size d = 0.80).The knee extension cutoffs identified were >7.1 cm2 for the COP area, >2.6 cm/s for the COP sway velocity in the anterior-posterior direction, and >3.2 cm/s for the mediolateral direction. Whereas, the 30° knee flexion cutoffs were >10.9 cm2 for the COP area, >2.9 cm/s for the COP sway velocity in the anterior-posterior direction, and >4.1 cm/s for the mediolateral direction. Both measures showed enough sensitivity and specificity (ie, area under the curve = 0.88 in and 0.80, respectively) to discriminate both groups.

CONCLUSIONS

The athletes with CLBP had poorer postural control than the healthy athletes and obtained specific cutoff scores from the COP values.

Treating low back pain - Bridging the gap between manual therapy and exercise

As therapists, we often recommend exercise to reduce patients' low-back pain, as well as increase their active range of motion and muscle strength. However, physical therapists face a challenge when recommending exercise to reduce low-back pain because the pain itself often inhibits the patient's ability to exercise or perform activities of daily living. This situation becomes even more challenging if the prescribed exercise program aggravates the individual's low-back pain. This article discusses a method which provides for the effective treatment of low back pain by allowing patients to exercise pain free earlier in the rehabilitation process. The method comprises a unique approach utilizing the following four components simultaneously from the onset of treatment: isometric muscle contraction (IMC); assisted active oscillatory mobilization; end-of-range passive stretch; and mindfulness.

Persons in remission from recurrent low back pain alter trunk coupling under dual-task interference during a dynamic balance task

This study investigated effects of cognitive dual-task interference and task prioritization instructions on task performance and trunk control during a dynamic balance task in persons with and without recurrent low back pain (rLBP). First, we tested the hypothesis that those with rLBP rely more on cognitive resources than back-healthy controls, and therefore trunk kinematics would be altered under dual-task interference conditions. Then, we tested participants' ability to modulate task performance in accord with prioritization instructions. Persons with and without rLBP (n = 19/group) performed the Balance-Dexterity Task, which involved single-limb balance while compressing an unstable spring with the other limb, with and without a cognitive task engaging verbal working memory. Trunk coupling was quantified with the coefficient of determination (R²) of an angle-angle plot of thorax-pelvis frontal plane motion. Task performance was quantified using variability of spring compression force and of cognitive task errors. Trunk coupling in the rLBP group was lower than that of the back-healthy control group in the single-task condition (p = 0.024) and increased in the dual-task condition (p = 0.006), abolishing the difference between groups. Significant main effects of task prioritization instruction on performance were observed with no differences between groups, indicating similar performance modulation. Cognitive task error variability decreased with a switch from a single- to dual-task condition, exposing an unexpected facilitation effect. We interpret these findings in the context of movement-specific reinvestment and action-specific perception theories as they pertain to cognitive contributions to posture and how the dual-task interference paradigm may influence those contributions.

Effects of age and sex on trunk motor control

The goal of the present study was to assess the effects of age and sex on trunk motor control. Fifty healthy adults (aged between 19 and 67 years, 28 males) participated in this study. Trunk motor control was assessed using force-controlled perturbations directly applied to the trunk. Admittance (inverse of lumped intrinsic and reflexive impedance) decreased with age and tended to be lower in females than males. The age effect on admittance was due to increasing intrinsic stiffness and damping with age, while intrinsic damping and position- and velocity feedback gains were lower in females than males. Feedback delays were not dependent on age. The decrease of trunk admittance with age is most likely due to increasing levels of antagonistic co-activation. Trunk admittance was (just) not significantly different between females and males, in spite of lower feedback gains and damping, possibly due to differences in trunk mass between sexes. These results imply that age and sex differences should be considered when assessing the relationship between back pain and trunk motor control.

September 2019 Letter to the Editor-in-Chief

Letter to the Editor-in-Chief of JOSPT as follows: "Highlighting Distinctions Between Discrete Perturbations and Continuous Perturbations in the Study of Dynamic Trunk Control" with Authors' Response J Orthop Sports Phys Ther 2019;49(9):679-681. doi:10.2519/jospt.2019.0201.

Time to Reflect on the Role of Motor Control in Low Back Pain

The articles in this special issue on low back pain are the outcome of work undertaken by a series of working parties established during the meeting, "State-of-the-Art in Motor Control and Low Back Pain: International Clinical and Research Expert Forum," held in Chicago in October 2015. This multidisciplinary meeting provided an opportunity for discussion of key issues that interconnect motor control, pain, and the spine. What started as a relatively straightforward objective to summarize the field subsequently developed into an extensive process of literature review and discussion that culminated in the commentaries and articles presented in this special issue. We hope that the up-to-date information and in-depth insights into pain, motor control, and rehabilitation provide novel insights and a clear trajectory for future work and form the foundation for ongoing lively discussion. J Orthop Sports Phys Ther 2019;49(6):367-369. doi:10.2519/jospt.2019.0104.

Changes in Structure and Function of the Back Muscles in Low Back Pain: Different Time Points, Observations, and Mechanisms

Spinal health depends on optimal back muscle performance, and this is determined by muscle structure and function. There has been substantial research evaluating the differences in structure and function of many back muscles, including the multifidus and erector spinae, but with considerable variation in results. Many studies have shown atrophy, fat infiltration, and connective tissue accumulation in back muscles, particularly deep fibers of the multifidus, but the results are not uniform. In terms of function, results are also somewhat inconsistent, often reporting lower multifidus activation and augmented recruitment of more superficial components of the multifidus and erector spinae, but, again, with variation between studies. A major recent observation has been the identification of time-dependent differences in features of back muscle adaptation, from acute to subacute/recurrent to chronic states of the condition. Further, these adaptations have been shown to be explained by different time-dependent mechanisms. This has substantial impact on the rationale for rehabilitation approaches. The aim of this commentary was to review and consolidate the breadth of research investigating adaptation in back muscle structure and function, to consider explanations for some of the variation between studies, and to propose how this model can be used to guide rehabilitation in a manner that is tailored to individual patients and to underlying mechanisms. J Orthop Sports Phys Ther 2019;49(6):464-476. doi:10.2519/jospt.2019.8827.