The Effects of Experimentally Induced Low Back Pain on Spine Rotational Stiffness and Local Dynamic Stability

The effects of soft vs. rigid back-support exoskeletons on trunk dynamic stability and trunk-pelvis coordination in young and old adults during repetitive lifting

While back-support exoskeletons are increasing in popularity as an ergonomic intervention for manual material handling, they may cause alterations to neuromuscular control required for maintaining spinal stability. This study evaluated the effects of soft and rigid passive exoskeletons on trunk local dynamic stability and trunk-pelvis coordination. Thiry-two young (18-30 years) and old (45-60 years) men and women completed repetitive lifting and lowering tasks using two different exoskeletons and in a control condition. Both exoskeletons significantly reduced the short-term maximum Lyapunov exponent (LyE) of the trunk (p < 0.01), suggesting improved local dynamic stability. There was also a significant main effect of age (p = 0.05): older adults exhibited lower short-term LyE that young adults. Use of the soft exoskeleton significantly increased, while the rigid exoskeleton significantly decreased, long-term LyE, and these changes were more pronounced in the young group compared to the old group. Additionally, exoskeleton use resulted in significant increase (p < 0.001) of mean absolute relative phase (MARP) and deviation phase (DP) by ∼30-60 %, with greater increases due to the rigid than the soft device. Thus, trunk-pelvic coordination and coordination variability were negatively impacted by exoskeleton use. Potential reasons for these findings may include exoskeleton-induced changes in lifting strategy, reduced peak trunk flexion velocity, and cycle-to-cycle variability of trunk velocity. Furthermore, although the soft and rigid devices caused comparable changes in trunk-extensor muscle activity, they exhibited differential effects on long-term maximum Lyapunov exponents as well as trunk-pelvic coordination, indicating that exoskeleton design features can have complex effects on trunk neuromuscular control.

Differences in dynamic balance control based on pain catastrophizing level in individuals with nonspecific chronic low back pain

BACKGROUND

Pain catastrophization (PC) is related to motor control changes in individuals with nonspecific chronic low back pain (NSCLBP). However, differences in dynamic balance control based on the level of PC still remain unclear in these individuals.

OBJECTIVE

The aim of this study was to compare the dynamic balance control between healthy controls and individuals with NSCLBP with high and low PC.

METHODS

Forty individuals with NSCLBP and 20 healthy participants were enrolled in this cross-sectional study. Individuals with NSCLBP were classified into two groups of high and low PC. Dynamic balance control was assessed using the Modified Star Excursion Balance Test (MSEBT), Five-Time Sit-to-Stand Test (FTSST), and Timed Up and Go Test (TUGT).

RESULTS

Statistical analyses showed that mean values of reach distances in the anterior, posteromedial, and posterolateral directions of the MSEBT were significantly lower in individuals with NSCLBP with high PC compared to low PC (p = .04, p = .01, and p = .04, respectively) and healthy controls (p < .001, p = .001, and p = .006, respectively). In addition, for both the FTSS and TUG tests, the mean time was significantly greater in individuals with NSCLBP with high PC compared to low PC (p < .001 and p = .004, respectively) and healthy controls (p < .001).

CONCLUSIONS

Our results showed poor dynamic balance control in individuals with NSCLBP with high PC. This suggests that PC could contribute to the impaired dynamic balance control in individuals with NSCLBP. Combining balance exercises and cognitive-behavioral treatments targeting PC may be useful for the improvement of dynamic balance control in individuals with NSCLBP with high PC.

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.

Exploring how metronome pacing at varying movement speeds influences local dynamic stability and coordination variability of lumbar spine motion during repetitive lifting

Auditory metronomes have been used to preserve movement consistency when examining local dynamic stability (LDS) and coordination variability (CV) of lumbar spine motion during repetitive movements. However, the potential influence of the metronome itself on these outcome measures has rarely been considered. Therefore, this study investigated the influence of different metronome paces (i.e., lifting speeds) on measures of lumbar spine LDS and thorax-pelvis CV during a repetitive lifting/lowering task in comparison to self-paced movements. Ten participants completed 5 repetitive lift/lower trials, where participants completed 35 consecutive repetitions (analysis on last 30 repetitions) at a self-selected pace for the first and last trial, and were paced by a 10 lift/min, 15 lift/min, and 20 lift/min metronome, in randomized order, for the remaining three trials. The average self-paced lift/lower speed before and after experiencing the three different metronome paced speeds was 16.2 (±1.02) and 17.2 (±0.73) lifts/min, respectively, and the most-preferred metronome pace trial was 15 lifts/min. Thorax-pelvis CV during the self-paced trials were similar (p > 0.05) to the 15 lift/min metronome paced trials, while greater thorax-pelvis CV was observed for the 10 lift/min compared to the 15 lift/min and 20 lift/min and second self-paced trial (all p < 0.026). This movement speed effect was not observed for lumbar spine LDS; however, more-dynamically stable movements were observed during all metronome paced trials in comparison to the self-paced trials. This study highlights that careful consideration is required when employing a metronome to control/manipulate movement characteristics while examining neuromuscular control using non-linear dynamical systems measures.

Neuromuscular adaptations to experimentally induced pain in the lumbar region: systematic review and meta-analysis

ABSTRACT

Experimental pain models are frequently used to understand the influence of pain on the control of human movement. In this systematic review, we assessed the effects of experimentally induced pain in the lumbar region of healthy individuals on trunk muscle activity and spine kinematics. Databases were searched from inception up to January 31, 2022. In total, 26 studies using either hypertonic saline injection (n = 19), heat thermal stimulation (n = 3), nociceptive electrical stimulation (n = 3), or capsaicin (n = 1) were included. The identified adaptations were task dependent, and their heterogeneity was partially explained by the experimental pain model adopted. Meta-analyses revealed an increase of erector spinae activity (standardized mean difference = 0.71, 95% confidence interval [CI] = 0.22-1.19) during full trunk flexion and delayed onset of transversus abdominis to postural perturbation tasks (mean difference = 25.2 ms, 95% CI = 4.09-46.30) in the presence of pain. Low quality of evidence supported an increase in the activity of the superficial lumbar muscles during locomotion and during voluntary trunk movements during painful conditions. By contrast, activity of erector spinae, deep multifidus, and transversus abdominis was reduced during postural perturbation tasks. Reduced range of motion of the lumbar spine in the presence of pain was supported by low quality of evidence. Given the agreement between our findings and the adaptations observed in clinical populations, the use of experimental pain models may help to better understand the mechanisms underlying motor adaptations to low back pain.

Effect of postural threat on motor control in people with and without low back pain

INTRODUCTION

Negative pain-related cognitions are associated with persistence of low-back pain (LBP), but the mechanism underlying this association is not well understood. We propose that negative pain-related cognitions determine how threatening a motor task will be perceived, which in turn will affect how lumbar movements are performed, possibly with negative long-term effects on pain.

OBJECTIVE

To assess the effect of postural threat on lumbar movement patterns in people with and without LBP, and to investigate whether this effect is associated with task-specific pain-related cognitions.

METHODS

30 back-healthy participants and 30 participants with LBP performed consecutive two trials of a seated repetitive reaching movement (45 times). During the first trial participants were threatened with mechanical perturbations, during the second trial participants were informed that the trial would be unperturbed. Movement patterns were characterized by temporal variability (CyclSD), local dynamic stability (LDE) and spatial variability (meanSD) of the relative lumbar Euler angles. Pain-related cognition was assessed with the task-specific 'Expected Back Strain'-scale (EBS). A three-way mixed Manova was used to assess the effect of Threat, Group (LBP vs control) and EBS (above vs below median) on lumbar movement patterns.

RESULTS

We found a main effect of threat on lumbar movement patterns. In the threat-condition, participants showed increased variability (MeanSDflexion-extension, p<0.000, η2 = 0.26; CyclSD, p = 0.003, η2 = 0.14) and decreased stability (LDE, p = 0.004, η2 = 0.14), indicating large effects of postural threat.

CONCLUSION

Postural threat increased variability and decreased stability of lumbar movements, regardless of group or EBS. These results suggest that perceived postural threat may underlie changes in motor behavior in patients with LBP. Since LBP is likely to impose such a threat, this could be a driver of changes in motor behavior in patients with LBP, as also supported by the higher spatial variability in the group with LBP and higher EBS in the reference condition.

The influence of experimental low back pain on neural networks involved in the control of lumbar erector spinae muscles

INTRODUCTION

Low back pain (LBP) often modifies spine motor control, but the neural origin of these motor control changes remains largely unexplored. This study aimed to determine the impact of experimental low back pain on the excitability of cortical, subcortical, and spinal networks involved in the control of back muscles.

METHOD

Thirty healthy subjects were recruited and allocated to Pain (capsaicin and heat) or Control (heat) groups. Corticospinal excitability (motor-evoked potential-MEP) and intracortical networks were assessed by single- and paired-pulse transcranial magnetic stimulation, respectively. Electrical vestibular stimulation was applied to assess vestibulospinal excitability (vestibular MEP-VMEP), and the stretch reflex for excitability of the spinal or supraspinal loop (R1 and R2, respectively). Evoked back motor responses were measured before, during and after pain induction. Nonparametric rank-based ANOVA determined if pain modulated motor neural networks.

RESULTS

A decrease of R1 amplitude was present after the pain disappearance (p=0.01) whereas an increase was observed in the control group (p=0.03) compared to the R1 amplitude measured at pre-pain and pre-heat period, respectively (Group x Time interaction - p<0.001). No difference in MEP and VMEP amplitude was present during and after pain (p>0.05).

CONCLUSION

During experimental LBP, no change in cortical, subcortical, or spinal networks was observed. After pain disappearance, the reduction of the R1 amplitude without modification of MEP and VMEP amplitude suggest a reduction in spinal excitability potentially combined with an increase in descending drives. The absence of effect during pain needs to be further explored.

Trunk Dynamic Stability Assessment for Individuals With and Without Nonspecific Low Back Pain During Repetitive Movement

OBJECTIVE

This study aimed to employ nonlinear dynamic approaches to assess trunk dynamic stability with speed, symmetry, and load during repetitive flexion-extension (FE) movements for individuals with and without nonspecific low back pain (NSLBP).

BACKGROUND

Repetitive trunk FE movement is a typical work-related LBP risk factor contingent on speed, symmetry, and load. Improper settings/adjustments of these control parameters could undermine the dynamic stability of the trunk, hence leading to low back injuries. The underlying stability mechanisms and associated control impairments during such dynamic movements remain elusive.

METHOD

Thirty-eight male volunteers (19 healthy, 19 NSLBP) enrolled in the current study. All participants performed repetitive trunk FE movements at high/low speeds, in symmetric/asymmetric directions, with/without a wearable loaded vest. Trunk instantaneous rotation angle was computed for each trial to be assessed in terms of local and orbital stability, using maximum finite-time Lyapunov exponents (LyEs) and Floquet multipliers (FMs), respectively.

RESULTS

Both groups demonstrated equivalent competency in terms of trunk control and stability, suggesting functional adaptation strategies may be used by the NSLBP group. Wearing the loaded vest magnified the effects of trunk control impairment for the NSLBP group. The combined presence of high-speed and symmetrical FE movements was associated with least trunk local stability.

CONCLUSION

Nonlinear dynamic techniques, particularly LyE, are potentially effective for assessing trunk dynamic stability dysfunction for individuals with NSLBP during various activities.

APPLICATION

This work can be applied toward the development of quantitative personalized spinal evaluation tools with a wide range of potential occupational and clinical applications.

Associations of low-back pain and pain-related cognitions with lumbar movement patterns during repetitive seated reaching

BACKGROUND

Development of more effective interventions for nonspecific chronic low back pain (LBP), requires a robust theoretical framework regarding mechanisms underlying the persistence of LBP. Altered movement patterns, possibly driven by pain-related cognitions, are assumed to drive pain persistence, but cogent evidence is missing.

AIM

To assess variability and stability of lumbar movement patterns, during repetitive seated reaching, in people with and without LBP, and to investigate whether these movement characteristics are associated with pain-related cognitions.

METHODS

60 participants were recruited, matched by age and sex (30 back-healthy and 30 with LBP). Mean age was 32.1 years (SD13.4). Mean Oswestry Disability Index-score in LBP-group was 15.7 (SD12.7). Pain-related cognitions were assessed by the 'Pain Catastrophizing Scale' (PCS), 'Pain Anxiety Symptoms Scale' (PASS) and the task-specific 'Expected Back Strain' scale(EBS). Participants performed a seated repetitive reaching movement (45 times), at self-selected speed. Lumbar movement patterns were assessed by an optical motion capture system recording positions of cluster markers, located on the spinous processes of S1 and T8. Movement patterns were characterized by the spatial variability (meanSD) of the lumbar Euler angles: flexion-extension, lateral-bending, axial-rotation, temporal variability (CyclSD) and local dynamic stability (LDE). Differences in movement patterns, between people with and without LBP and with high and low levels of pain-related cognitions, were assessed with factorial MANOVA.

RESULTS

We found no main effect of LBP on variability and stability, but there was a significant interaction effect of group and EBS. In the LBP-group, participants with high levels of EBS, showed increased MeanSD_{lateral-bending} (p = 0.004, η² = 0.14), indicating a large effect. MeanSD_{axial-rotation} approached significance (p = 0.06).

SIGNIFICANCE

In people with LBP, spatial variability was predicted by the task-specific EBS, but not by the general measures of pain-related cognitions. These results suggest that a high level of EBS is a driver of increased spatial variability, in participants with LBP.

Segmental Chiropractic Spinal Manipulation Does not Reduce Pain Amplification and the Associated Pain-Related Brain Activity in a Capsaicin-Heat Pain Model

Musculoskeletal injuries lead to sensitization of nociceptors and primary hyperalgesia (hypersensitivity to painful stimuli). This occurs with back injuries, which are associated with acute pain and increased pain sensitivity at the site of injury. In some cases, back pain persists and leads to central sensitization and chronic pain. Thus, reducing primary hyperalgesia to prevent central sensitization may limit the transition from acute to chronic back pain. It has been shown that spinal manipulation (SM) reduces experimental and clinical pain, but the effect of SM on primary hyperalgesia and hypersensitivity to painful stimuli remains unclear. The goal of the present study was to investigate the effect of SM on pain hypersensitivity using a capsaicin-heat pain model. Laser stimulation was used to evoke heat pain and the associated brain activity, which were measured to assess their modulation by SM. Eighty healthy participants were recruited and randomly assigned to one of the four experimental groups: inert cream and no intervention; capsaicin cream and no intervention; capsaicin cream and SM at T7; capsaicin cream and placebo. Inert or capsaicin cream (1%) was applied to the T9 area. SM or placebo were performed 25 min after cream application. A series of laser stimuli were delivered on the area of cream application (1) before cream application, (2) after cream application but before SM or placebo, and (3) after SM or placebo. Capsaicin cream induced a significant increase in laser pain (p < 0.001) and laser-evoked potential amplitude (p < 0.001). However, SM did not decrease the amplification of laser pain or laser-evoked potentials by capsaicin. These results indicate that segmental SM does not reduce pain hypersensitivity and the associated pain-related brain activity in a capsaicin-heat pain model.

Concurrent validity of a custom computer vision algorithm for measuring lumbar spine motion from RGB-D camera depth data

Using RGB-D cameras as an alternative motion capture device can be advantageous for biomechanical spine motion assessments of movement quality and dysfunction due to their lower cost and complexity. In this study, we evaluated RGB-D camera performance relative to gold-standard optoelectronic motion capture equipment. Twelve healthy young adults (6M, 6F) were recruited to perform repetitive spine flexion-extension, while wearing infrared reflective marker clusters placed over their T₁₀-T₁₂ spinous processes and sacrum, and motion capture data were recorded simultaneously by both systems. Custom computer vision algorithms were developed to extract spine angles from depth data. Root mean square error (RMSE) was calculated for continuous Euler angles, and intraclass correlation coefficients (ICC_2,1) were calculated between minimum and maximum angles and range of motion in all movement planes. RMSE was low (RMSE ≤ 2.05°) and reliability was good to excellent (0.849 ≤ ICC_2,1 ≤ 0.979) across all movement planes. In conclusion, the proposed algorithm for tracking 3D lumbar spine motion during a sagittal movement task from one RGB-D camera is reliable in comparison to gold-standard motion tracking equipment. Future research will investigate accuracy and validity in a wider variety of movements, and will also investigate the development of novel methods to measure spine motion without using infrared reflective markers.

Changes in Trunk Variability and Stability of Gait in Patients with Chronic Low Back Pain: Impact of Laboratory versus Daily-Living Environments

BACKGROUND

Individuals with chronic low back pain (CLBP) experience changes in gait control due to pain and/or fear. Although CLBP patients' gait has been performed in laboratory environments, changes in gait control as an adaptation to unstructured daily living environments may be more pronounced than the corresponding changes in laboratory environments. We investigated the impacts of the environment and pathology on the trunk variability and stability of gait in CLBP patients.

METHODS

CLBP patients (n=20) and healthy controls with no low-back pain history (n=20) were tasked with walking in a laboratory or daily-living environment while wearing an accelerometer on the low back. We calculated the stride-to-stride standard deviation and multiscale sample entropy as indices of "gait variability" and the maximum Lyapunov exponent as an index of "gait stability" in both the anterior-posterior and medial-lateral directions. The participants were assessed on the numerical rating scale for pain intensity, the Tampa Scale for Kinesiophobia, and the Roland-Morris Disability Questionnaire for quality of life (QOL).

RESULTS

In a repeated-measures ANOVA, the standard deviation was affected by environment in the anterior-posterior direction and by group and environment in the medial-lateral direction. Multiscale sample entropy showed no effect in the anterior-posterior direction and showed both effects in the medial-lateral direction. Maximum Lyapunov exponents showed both effects in the anterior-posterior direction, but none in the medial-lateral direction. These changes of trunk motor control by CLBP patients were found to be related to pain intensity, fear of movement, and/or QOL in the daily-living environment but not in the laboratory environment.

CONCLUSION

These results revealed that CLBP patients exhibit changes in trunk variability and stability of gait depending on the environment, and they demonstrated that these changes are related to pain, fear, and QOL. We propose useful accelerometer-based assessments of qualitative gait in CLBP patients' daily lives, as it would provide information not available in a general practice setting.

Beyond the mechanical lens: Systemic inflammatory responses to repetitive lifting under varying loads and frequencies

OBJECTIVE

Currently, low back disorder (LBD) research focuses primarily on mechanical variables to assess whether task demands exceed tissue capacity; however, it is important to assess how other nonmechanical variables affect tissue capacity in a time-dependent manner. The current investigation sought to explore physiological responses to an acute lifting task, as lifting has been implicated as a risk factor in the development of LBDs.

METHODS

Twelve participants completed two sessions of 2 h of repetitive symmetrical lifting from floor to knuckle height under two conditions, matched for total external work (Low Force High Repetition (LFHR) and High Force Low Repetition (HFLR)). Full-body kinematics and ground reaction forces were measured throughout. Interleukin 6 (IL-6) and interleukin 8 (IL-8), markers of systemic inflammation, were assessed from blood sampling at Baseline, 0, 4 and 24 h post-lifting on both days. Dual x-ray absorptiometry (DEXA) scans were also performed on participants to quantify body composition.

RESULTS

Significant load (HFLR and LFHR) * time (Baseline, 0, 4, 24 h) interaction effects were found for both IL-6 and IL-8, where the LFHR condition resulted in greater responses at 0 and 4 h post-lifting.

CONCLUSIONS

This was the first study of its kind to concurrently measure peak and cumulative spinal moments and their relationship to systemic inflammation in both sexes, while strictly controlling for confounding variables (e.g. physical activity, caloric intake, body composition, etc.). Greater levels of IL-6 and IL-8 were seen in the LFHR condition, likely due to the greater cumulative spinal moments in this condition.

The immediate and prolonged effects of military body armor on the relative timing of thorax and pelvis rotations during toe-touch and two-legged squat tasks

Although military body armor is an effective life saver, it considerably loads more weight on the warfighters, increasing the risk of musculoskeletal injury. This study investigated the immediate and prolonged effects of wearing body armor on timing aspect of lumbo-pelvic coordination during the toe-touch (TT) and two-legged-squat (TLS) tests. A cross-over study design was used wherein twelve asymptomatic and gender-balanced individuals completed two experimental sessions with and without body armor. A session included two similar sets of tests, before and after exposure to a treadmill walk, containing a TT and a TLS test with ten cycles of fast bending and return. Reflective markers were attached on the participants to capture the kinematics of body segments in conjunction with a motion capture system. The mean absolute relative phase (MARP) and deviation phase (DP) between the thorax and pelvis were calculated for each test. The pre-walk MARP in the return was significantly larger with versus without body armor (p = 0.022), while there were no significant effects of body armor on the other outcome measures. In addition, the pre-walk MARP and DP in the bending and return, as well as the walk-induced changes in the MARP in the bending phase were significantly larger in TLS versus TT (p < 0.026). Therefore, using a body armor immediately made the lumbo-pelvic coordination less in-phase during return, but no prolonged effects were found. Further investigation is necessary to specify chances wearing a body armor increases the risk of musculoskeletal injuries in the lower back and lower extremities joints.

Intervertebral disc herniation effects on multifidus muscle composition and resident stem cell populations

BACKGROUND

Paraspinal muscles are crucial for vertebral stabilization and movement. These muscles are prone to develop fatty infiltration (FI), fibrosis, and atrophy in many spine conditions. Fibro-adipogenic progenitors (FAPs), a resident muscle stem cell population, are the main contributors of muscle fibrosis and FI. FAPs are involved in a complex interplay with satellite cells (SCs), the primary myogenic progenitor cells within muscle. Little is known about the stem cell composition of the multifidus. The aim of this study is to examine FAPs and SCs in the multifidus in disc herniation patients. Multifidus muscle samples were collected from 10 patients undergoing decompressive spine surgery for lumbar disc herniation. Hamstring muscle was collected from four patients undergoing hamstring autograft ACL reconstruction as an appendicular control. Multifidus tissue was analyzed for FI and fibrosis using Oil-Red-O and Masson's trichrome staining. FAPs and SCs were visualized using immunostaining and quantified with fluorescence-activated cell sorting (FACS) sorting. Gene expression of these cells from the multifidus were analyzed with reverse transcription-polymerase chain reaction and compared to those from hamstring muscle. FI and fibrosis accounted for 14.2%± 7.4% and 14.8%±4.2% of multifidus muscle, respectively. The multifidus contained more FAPs (11.7%±1.9% vs 1.4%±0.2%; P<.001) and more SCs (3.4%±1.6% vs 0.08%±0.02%; P=.002) than the hamstring. FAPs had greater α Smooth Muscle Actin (αSMA) and adipogenic gene expression than FAPs from the hamstring. SCs from the multifidus displayed upregulated expression of stem, proliferation, and differentiation genes.

CONCLUSION

The multifidus in patients with disc herniation contains large percentages of FAPs and SCs with different gene expression profiles compared to those in the hamstring. These results may help explain the tendency for the multifidus to atrophy and form FI and fibrosis as well as elucidate potential approaches for mitigating these degenerative changes by leveraging these muscle stem cell populations.

Characterizing Local Dynamic Stability of Lumbar Spine Sub-regions During Repetitive Trunk Flexion-Extension Movements

Using a technique of tracking intersegmental spine kinematics via skin surface markers, this study aimed to estimate local dynamic spine stability across smaller sub-regions (or segments) of the lumbar spine while also considering the impact of an external pelvic constraint during repetitive movements. Sixteen participants (10 males) performed two trials [Free Motion (FM), Pelvis Constrained (PC)] each consisting of 65 repetitive trunk flexion-extension movements to assess dynamic spine stability using maximum Lyapunov exponents (LyE). First, results indicated that LyE obtained from analysis of 30 repetitive flexion-extension movements did not differ from those obtained from analysis of greater numbers of repetitive movements, which aligns with results from a previous study for the whole lumbar spine. Next, for both males and females, and FM and PC trials, the most caudal region of the lumbar spine behaved the most dynamically stable, while upper lumbar regions behaved the most dynamically unstable. Finally, females demonstrated greater lumbar and intersegmental stability (lower LyE) during PC trials compared to FM, while males demonstrated slightly decreased lumbar and intersegmental stability (higher LyE) during PC trials compared to FM; this resulted in PC trials, but not FM trials, being different between sexes. Altogether, these data show that dynamic stability of lumbar spine sub-regions may be related to the proximity of the motion segment to rigid skeletal structures, and that consideration is needed when deciding whether to constrain the pelvis during analyses of dynamic spine stability.

Concurrent validity of a wearable IMU for objective assessments of functional movement quality and control of the lumbar spine

Inertial measurement units (IMUs) are being recognized in clinical and rehabilitation settings for their ability to assess movement-related disorders of the spine for better guidance of treatment-planning and tracking of recovery. This study evaluated the Mbientlab MetaMotionR IMUs, relative to Vicon motion capture equipment in measuring local dynamic stability of the spine (quantified using maximum finite-time Lyapunov exponent; λ_max), lumbopelvic coordination (quantified using mean absolute relative phase; MARP), and intersegmental motor variability (quantified using deviation phase; DP) of lumbopelvic segments in 10 participants during 35 cycles of repetitive spine flexion-extension (FE). Intraclass correlations were strong between systems when using both the FE angle time-series and the sum of squares (SS) time-series to measure local dynamic stability (0.807 ≤ICC_2,1^λmax,FE ≤ 0.919; 0.738 ≤ ICC_2,1^λmax,SS ≤ 0.868), sagittal-plane lumbopelvic coordination (0.961 ≤ICC_2,1^MARP ≤ 0.963), and sagittal-plane lumbopelvic variability (0.961 ≤ICC_2,1^DP ≤ 0.963). It was concluded that the MetaMotionR IMUs can be reliably used for measuring features associated with spine movement quality and motor control during a repetitive FE task. Future work will assess the reliability of sensor placement, performance during multi-directional movements, and ability to discern clinical and healthy populations based on assessment of movement quality and control.

The effects of protective footwear on spine control and lifting mechanics

Manual materials handling is often performed in hazardous environments where protective footwear must be worn; however, workers can wear different types of footwear depending on the hazards present. Therefore, the goal of this study was to investigate how three-dimensional lifting mechanics and trunk local dynamic stability are affected by different types of protective footwear (i.e. steel-toed shoes (unlaced boot), steel-toed boots (work boot), and steel-toed boots with a metatarsal guard (MET)). Twelve males and twelve females performed a repetitive lifting task at 10% of their maximum lifting effort, under three randomized footwear conditions. Footwear type influenced ankle range of motion (ROM). The work boot condition reduced ankle sagittal ROM (p = 0.007) and the MET condition reduced ankle ROM in the sagittal (p = 0.004), frontal (p = 0.001) and transverse (p = 0.003) planes. Despite these differences at the ankle, no other changes in participant lifting mechanics were observed.

Effects of Reiki Versus Physiotherapy on Relieving Lower Back Pain and Improving Activities Daily Living of Patients With Intervertebral Disc Hernia

Patients with intervertebral disc herniation (IVDH) seek complementary and conventional medical therapies to manage related problems. This study aimed to determine the effectiveness of Reiki compared with physiotherapy to relieve the lower back pain intensity and to improve the activities of daily living (ADL) in the IDVH patients. In this clinical trial study, 60 patients with IVDH were randomly assigned to one of the Reiki, physiotherapy, and drug therapy groups. The severity of pain and the ADL were measured using visual analog scale (VAS) pain and ADL–Instrumental ADL questionnaire before and after the intervention. A significant difference was found in pain intensity and ADL improvement between Reiki and the drug therapy. However, there was no significant difference between Reiki and physiotherapy groups in managing pain and improving ADL. Reiki and physiotherapy are effective methods in managing pain and improving ADL in patients with IVDH; however, Reiki is more cost-effective and faster treatment method than physiotherapy.

Differential effects of muscle fatigue on dynamic spine stability: Implications for injury risk

This study was designed to assess the utility of using a measure of dynamic spine stability in an unfatigued, rested state as a predictor of dynamic spine stability in a challenged, fatigued state. Participants completed three trials (Day 1: Rested, Fatigued; Day 2: Recovery) during which the dynamic stability of the spine was assessed over 30 repeated flexion/extension motions using maximum finite-cycle Lyapunov exponents. Multiple sets of dynamic trunk extensions were performed to fatigue the trunk extensor muscles. Across the sample population, an increase in dynamic spine stability when fatigued was observed, as well as a moderate correlation between the level of dynamic stability when rested and a stabilizing response when fatigued. Further analysis of the data on a person-by-person basis revealed three distinct responses in which participants either stabilized, destabilized or had no change in dynamic spine stability when fatigued. Therefore, the mean response of the sample population did not adequately represent the true, meaningful response of individuals within the population. These results illustrate the importance of considering individualized responses when examining dynamic stability measures, and provide preliminary evidence that suggests that individual injury risk cannot be completely captured by measures taken in an unchallenged, rested state.

The effect of attentional focus on local dynamic stability during a repetitive spine flexion task

The association between low back pain and spine movement control suggests that it is important to reliably quantify movement behavior. One method to characterize spine movement behavior is to measure the local dynamic stability (LDS) of spine movement during a repetitive flexion task in which a participant is asked to touch multiple targets repetitively. Within the literature, it has been well established that an individual's focus of attention (FOA) can modulate their neuromuscular control and affect task performance. The goal of this project was to examine the unknown effect of FOA on LDS measurements and timing error during a repetitive spine flexion task that is commonly used to assess movement control. Fourteen healthy adults (7 male) were instructed to touch two targets (shoulder height and knee height) to the beat of a metronome (4 s/cycle) for 35 consecutive cycles. They completed this task under internal (focus on trunk movement) and external (focus on targets) FOA conditions. Motion capture data of the trunk and sacrum were collected at 120 Hz. The lumbar spine angle was defined as the orientation of the trunk relative to the pelvis. The local divergence exponent (λ_max) was calculated from the sum of squares of the 3-dimensional spine angle. Timing error was calculated as the time difference between target touches and metronome beats. Changing an individual's FOA had no effect on λ_max calculations or timing error. Although clear task instructions are important, it is not essential to control for FOA during this movement assessment protocol.

Variations of handheld loads increase the range of motion of the lumbar spine without compromising local dynamic stability during walking

BACKGROUND

Walking is often considered a beneficial management strategy for certain populations of low back pain patients. However, little is known about how simple challenges that people often encounter, such as carrying loads in the hands, affect the low back during walking.

RESEARCH QUESTION

How do variations in hand loading affect arm swing, lumbar spine range of motion (ROM), and lumbar spine local dynamic stability (LDS) during walking?

METHODS

Sixteen young healthy participants (8 female) performed nine treadmill walking trials, each at 1.25 m/s for 3 consecutive minutes. Conditions manipulated the magnitude of hand loads (unloaded, low, high) and location of hand loads (directly in hands, in bags). Kinematic markers were used to measure sagittal plane arm swing, 3D lumbar spine ROM, and lumbar spine LDS during each trial.

RESULTS

Arm swing was significantly (p < 0.001) reduced as load increased directly in the hands; however, when held in bags load magnitude had no effect. Further, arm swing was significantly (p < 0.0001) lower when loads were held in bags. Lumbar flexion/extension ROM was greatest with the low load compared to both unloaded (p = 0.012) and high load (p = 0.0717) conditions, and was also greater (p < 0.0001) with loads held directly in the hands compared to loads in bags. Despite these changes in lumbar spine ROM, lumbar spine LDS was not significantly affected by any of the variations in hand loading.

SIGNIFICANCE

The greater lumbar spine cyclic motion, elicited by low hand loads held directly in the hands during walking, may be beneficial to the health of the low back. No changes in lumbar LDS were found, thereby suggesting that the small, likely beneficial, increases in lumbar spine ROM are well controlled by the motor control system and do not create an increased risk of injury.

Relationships between muscle electrical activity and the control of inter-vertebral motion during a forward bending task

Muscle strengthening exercises are commonly used in primary care for the treatment of chronic, non-specific low back pain (CNSLBP) as it has been theorised that increased muscle activity contributes to the stabilisation of inter-vertebral motion segments during bending and other spinal movements, however this has never been demonstrated in vivo. This study used contemporaneous quantitative fluoroscopy (QF) and surface electromyography (sEMG) to investigate relationships between continuous inter-vertebral motion variables and muscle electrical activity in the lumbar multifidus (LMU), lumbar and thoracic erector spinae (LES and TES) during standardised lumbar flexion and return in 18 healthy male human subjects. Our results demonstrated that the variability in the sharing of angular motion (i.e. Motion Share Variability MSV) and motion segment laxity during a bending task were significantly (p < 0.05) negatively correlated (Spearman) with muscle electrical activity throughout the participant bend for both locally and globally acting muscle groups. MSV was also strongly correlated with L2-3 laxity. The former suggests a damping mechanism reducing irregular displacements (i.e. less variability in the sharing of segmental motion) during bending and an action of spinal stabilisation by muscles at segmental levels, and the latter a synergy between laxity at L2-3 and MSV. While this has previously been theorised, it has never been shown in vivo at the inter-vertebral level. These assessments may be considered for use in validation studies of exercise programs for CNSLBP, however further replication is required.

Muscle Strength and Neuromuscular Control in Low-Back Pain: Elite Athletes Versus General Population

The purpose of the study was to investigate the athletic-based specificity of muscle strength and neuromuscular control of spine stability in chronic non-specific low-back pain (LBP). Thirty elite athletes and 29 age-matched non-athletes with (15 athletes and 15 non-athletes) and without LBP (15 athletes and 14 non-athletes) participated in the study. Muscle strength was measured during maximal isometric trunk flexion and trunk extension contractions. The neuromuscular control of spine stability was analyzed by determining trunk stiffness, trunk damping, and onset times of the lumbar and thoracic erector spinae muscles after sudden perturbations (quick release experiments) as well as maximum Lyapunov exponents (local dynamic stability) using non-linear time series analysis of repetitive lifting movements. LBP was assessed using the visual analog scale. We found lower maximal trunk extension moments (p = 0.03), higher trunk damping (p = 0.018) and shorter onset times (p = 0.03) of the investigated trunk muscles in LBP patients in both athletes and non-athletes. Trunk stiffness and the local dynamic stability did not show any differences (p = 0.136 and p = 0.375, respectively) between LBP patients and healthy controls in both groups. It can be concluded that, despite the high-level of training in athletes, both athletes and non-athletes with LBP showed the same deconditioning of the lumbar extensor muscles and developed similar strategies to ensure spine stability after sudden perturbations to protect the spine from pain and damage. The findings highlight that specific training interventions for the trunk muscles are not only crucial for individuals of the general population, but also for well-trained athletes.

A random-perturbation therapy in chronic non-specific low-back pain patients: a randomised controlled trial

The purpose of the study was to assess the effectiveness of a specific rehabilitation therapy for chronic non-specific low-back pain patients, based on a random/irregular functional perturbation training induced by force disturbances to the spine. Forty patients (20 controls and 20 in the perturbation-based group) finished the whole experimental design. A random-perturbation exercise, which included variable and unpredictable disturbances, was implemented in the therapy of the perturbation-based group (13 weeks, two times per week and 1.5 h per session). The participants of the control group did not receive any specific training. Low-back pain, muscle strength, and neuromuscular control of spine stability were investigated before and after the therapy using the visual analog scale, maximal isometric and isokinetic contractions, nonlinear time series analysis, and by determining the stiffness and damping of the trunk after sudden perturbations. The perturbation-based therapy reduced patient's low-back pain (35%), increased muscle strength (15-22%), and trunk stiffness (13%), while no significant changes were observed in the control group. It can be concluded that the proposed therapy has the potential to enhance trunk muscle capability as well as sensory information processing within the motor system during sudden loading and, as a consequence, improve the stabilization of the trunk.

Wearing an Inflatable Vest Alters Muscle Activation and Trunk Angle While Paddling a Surfboard

Low back pain is a commonly reported problem among recreational surfers. Some individuals report that wearing a vest with an inflatable bladder that alters trunk angle may help to alleviate pain. The purpose of this study was to determine whether such a vest has an effect on muscle activation and extension of the lower back. Twelve recreational surfers completed 12 paddling trials at 1.1 m/s in a swim flume on both a shortboard and a longboard on 2 separate days. Three conditions of no vest, vest uninflated, and vest inflated were presented to participants in random order. Surface EMG and trunk angle were acquired via wireless sensors placed over the right erector spinae, mid-trapezius, upper trapezius, and latissimus dorsi. Wearing the inflated vest affected muscle activation: erector spinae and mid-trapezius demonstrated a significant decrease in activation relative to wearing no vest (12% and 18% respectively, p < .05). Trunk extension was also significantly reduced when the vest was inflated (18% reduction, p < .05). Results were similar for both the short and longboard, though this effect was greater while paddling the larger board. These results suggest that a properly inflated vest can alter trunk extension and muscle activity while paddling a surfboard in water.

Differences in kinematics of the lumbar spine and lower extremities between people with and without low back pain during the down phase of a pick up task, an observational study

BACKGROUND

Limited research exists on lumbar spine and lower extremity movement during functional tasks in people with and without low back pain (LBP).

OBJECTIVE

To determine differences in lumbar spine and lower extremity kinematics in people with and without LBP during the down phase of a pick up task.

DESIGN

Cross-sectional, observational study.

METHOD

35 people (14 M, 21 F, 26.9 ± 10.9 years, 24.8 ± 3.2 kg/m2); 18 with and 17 without LBP were matched based on age, gender and BMI. Kinematics of the lumbar spine and lower extremities were measured using 3D motion capture, while subjects picked up an object off the floor. People with LBP were examined and assigned to movement-based LBP subgroups. Repeated measures ANOVA tests were conducted to determine the effect of group and region on lumbar spine and lower extremity kinematics. A secondary analysis was conducted to examine the effect of LBP subgroup on lumbar spine kinematics.

RESULTS

Compared to controls, subjects with LBP displayed greater upper and less lower lumbar flexion (P < 0.05), and more lumbar flexion during the first 25% of the pick up task (P < 0.01). There were no group differences in frontal or axial plane lumbar spine kinematics. Subjects with LBP displayed more frontal plane movement at the knee than control subjects (P < 0.01). There were no significant effects of movement-based LBP subgroup on kinematics (P > 0.05).

CONCLUSIONS

When evaluating movement during a functional task, the clinician should consider regional differences in the lumbar spine, pattern of movement, and lower extremity movement.

Low back skin sensitivity has minimal impact on active lumbar spine proprioception and stability in healthy adults

The purpose of the current work was to (1) determine whether low back cutaneous sensitivity could be reduced through the use of a topical lidocaine-prilocaine anesthetic (EMLA(®)) to mirror reductions reported in chronic lower back pain (CLBP) patients, as well as to (2) identify whether reductions in cutaneous sensitivity resulted in decreased lumbar spine proprioception, neuromuscular control and dynamic stability. Twenty-eight healthy participants were divided equally into matched EMLA and PLACEBO treatment groups. Groups completed cutaneous minimum monofilament and two-point discrimination (TPD) threshold tests, as well as tests of sagittal and axial lumbar spine active repositioning error, seated balance and repeated lifting dynamic stability. These tests were administered both before and after the application of an EMLA or PLACEBO treatment. Results show that low back minimum monofilament and TPD thresholds were significantly increased within the EMLA group. Skin sensitivity remained unchanged in the PLACEBO group. In the EMLA group, decreases in low back cutaneous sensitivity had minimal effect on low back proprioception (active sagittal and axial repositioning) and dynamic stability (seated balance and repeated lifting). These findings demonstrate that treating the skin of the low back with an EMLA anesthetic can effectively decrease the cutaneous sensitivity of low back region. Further, these decreases in peripheral cutaneous sensitivity are similar in magnitude to those reported in CLBP patients. Within this healthy population, decreased cutaneous sensitivity of the low back region has minimal influence on active lumbar spine proprioception, neuromuscular control and dynamic stability.

The acute effects of targeted abdominal muscle activation training on spine stability and neuromuscular control

Background

Targeted activation of the transversus abdominis (TrA) muscle through the abdominal drawing-in maneuver (ADIM) is a frequently prescribed exercise for the prevention and rehabilitation of low back pain. However, there is still debate over the role the ADIM plays in maintaining a stable spine during movement. Thus, a single cohort pre/post-intervention protocol was used to examine whether 5 min of ADIM training prior to a dynamic movement task alters dynamic spine stability and control.

Methods

Thirteen healthy participants performed a repetitive spine flexion task twice, once before and once after they received biofeedback training on how to correctly perform the ADIM in standing. Abdominal and back muscle activation (indwelling and surface electromyography, EMG) and 3D kinematic data were recorded during all trials. EMG activation (percent maximum) and local dynamic stability of spine movement [maximum finite-time Lyapunov exponent (λ_max)] were compared before and after the training using Friedman’s rank test and repeated-measures ANOVA, respectively. To assess the moderating effects of absolute changes in EMG (∆EMG) of each muscle after training on changes in stability, the ∆EMG (peak and mean) were added to the ANOVA as separate covariates (ANCOVA).

Results

Following ADIM training, there were greater peak and mean levels of activation in all tested abdominal muscles, including TrA, (p < 0.05), but not in the back muscles. The ANOVA showed no significant change in λ_max following training (p = 0.633). However, after considering the moderating effects of the ∆EMG seen in each muscle with training, it was found that only changes in TrA EMG significantly influenced stability. The ANCOVA revealed a significant main effect of training on stability as well as a significant interaction effect between training and ∆EMG recorded from TrA (p < 0.05); those with larger increases in TrA activation demonstrated larger improvements in stability.

Conclusion

As a group, 5 min of ADIM training did not change spine stability during dynamic movement. However, those who were most successful in improving TrA activation with a 5-min ADIM training session showed the greatest improvements in local dynamic spine stability after training. As such, dynamic spine stability in some individuals may benefit from ADIM training.

Electronic supplementary material

The online version of this article (doi:10.1186/s12984-016-0126-9) contains supplementary material, which is available to authorized users.

Effects of noxious stimulation to the back or calf muscles on gait stability

Gait stability is the ability to deal with small perturbations that naturally occur during walking. Changes in motor control caused by pain could affect this ability. This study investigated whether nociceptive stimulation (hypertonic saline injection) in a low back (LBP) or calf (CalfP) muscle affects gait stability. Sixteen participants walked on a treadmill at 0.94ms(-1) and 1.67ms(-1), while thorax kinematics were recorded using 3D-motion capture. From 110 strides, stability (local divergence exponent, LDE), stride-to-stride variability and root mean squares (RMS) of thorax linear velocities were calculated along the three movement axes. At 0.94ms(-1), independent of movement axes, gait stability was lower (higher LDE) and stride-to-stride variability was higher, during LBP and CalfP than no pain. This was more pronounced during CalfP, likely explained by the biomechanical function of calf muscles in gait, as supported by greater mediolateral RMS and stance time asymmetry than in LBP and no pain. At 1.67ms(-1), independent of movement axes, gait stability was greater and stride-to-stride variability was smaller with LBP than no pain and CalfP, whereas CalfP was not different from no pain. Opposite effects of LBP on gait stability between speeds suggests a more protective strategy at the faster speed. Although mediolateral RMS was greater and participants had more asymmetric stance times with CalfP than LBP and no pain, limited effect of CalfP at the faster speed could relate to greater kinematic constraints and smaller effects of calf muscle activity on propulsion at this speed. In conclusion, pain effects on gait stability depend on pain location and walking speed.

The effect of different ranges of motion on local dynamic stability of the elbow during unloaded repetitive flexion-extension movements

Local dynamic stability (LDS) of movement is controlled primarily by active muscles, and is known to be influenced by factors such as movement speed and inertial load. Other factors such as muscle length, the length of the target trajectory, and the resistance of passive tissues through ranges of motion (ROM) may also influence LDS. This study was designed to examine the effect of ROM, which impacts each of the aforementioned factors, on LDS of the elbow. 16 participants performed 30 unloaded, repetitive, flexion-extension movements of the elbow with varying (1) angular displacement magnitudes: 40° and 80°; (2) locations of ROM: mid-range, flexion end-range, extension end-range; and (3) rotated positions of the forearm: pronated and supinated. LDS was calculated using a finite time Lyapunov analysis of angular elbow flexion-extension kinematic data. EMG-based muscle activation and co-contraction data were also examined for possible mechanisms of stabilization. Results showed no changes in LDS with any movement condition; however, there were significant effects on muscle activation with ROM location and forearm rotated position. This suggests that a consistent level of LDS of the elbow through varying ROMs is maintained, at least in part, by the active control of the elbow flexor and extensor muscles.