Methods for assessment of trunk stabilization, a systematic review

Intra-day, short- and long-term reliability of surface electromyographic measurements during a standardized measurement protocol for lower back pain patients

BackgroundThe identification of back muscle dysfunction is a prerequisite for successful rehabilitation. Therefore, surface electromyography can be used for diagnostic and evaluative purposes. However, data quality highly depends on a) variance and inaccuracies in methodological procedures and b) on time-dependent changes, particularly in complex conditions such as chronic low back pain.ObjectiveTo assess intra-day, short-term and long-term reliability of a protocol designed for electromyographic measurements of the paraspinal muscles.MethodsThree everyday tasks were selected for measurement in two healthy populations (mean age (years): 26.25/30.49 (SD: 7.05/11.03), sex-balanced). The procedure follows a detailed protocol (e.g., including ultrasound, electrode placement, movement commands). Intraclass correlation coefficient (ICC), standard error of measurement (SEM) and minimum detectable change (MDC) were calculated.ResultsProne extension task demonstrated excellent test-retest agreement in all timespans (ICC = 0.92-0.96, SEM = 6.08-8.11, MDC = 16.85-22.49). Forward bending reliability ranged from moderate in long-term (ICC = 0.68-0.71, SEM = 1.98-2.52, MDC = 5.48-6.99) to good in intra-day (ICC = 0.76-0.89, SEM = 1.73-2.15, MDC = 4.79-5.95) to excellent in short-term assessment (ICC = 0.97, SEM = 1.07-1.21, MDC = 2.96-3.34). Sitting task showed the lowest test-retest agreement ranging between good to moderate in intra-day (ICC = 0.60-0.77, SEM = 1.22-1.26, MDC = 1.61-3.48)) and short-term reliability (ICC = 0.50-0.75, SEM = 1.24-2.06, MDC = 0.62-4.04) and moderate in long-term reliability (ICC = 0.65-0.71, SEM = 1.43-1.85, MDC = 3.95-5.12).ConclusionUsing standardized procedures, surface electromyography can provide reliable data for practitioners in low back pain rehabilitation. Timespan had a limited influence on reliability compared to the type of task performed.

Trunk postural control during unstable sitting among individuals with and without low back pain: A systematic review with an individual participant data meta-analysis

INTRODUCTION

Sitting on an unstable surface is a common paradigm to investigate trunk postural control among individuals with low back pain (LBP), by minimizing the influence lower extremities on balance control. Outcomes of many small studies are inconsistent (e.g., some find differences between groups while others do not), potentially due to confounding factors such as age, sex, body mass index [BMI], or clinical presentations. We conducted a systematic review with an individual participant data (IPD) meta-analysis to investigate whether trunk postural control differs between those with and without LBP, and whether the difference between groups is impacted by vision and potential confounding factors.

METHODS

We completed this review according to PRISMA-IPD guidelines. The literature was screened (up to 7th September 2023) from five electronic databases: MEDLINE, CINAHL, Embase, Scopus, and Web of Science Core Collection. Outcome measures were extracted that describe unstable seat movements, specifically centre of pressure or seat angle. Our main analyses included: 1) a two-stage IPD meta-analysis to assess the difference between groups and their interaction with age, sex, BMI, and vision on trunk postural control; 2) and a two-stage IPD meta-regression to determine the effects of LBP clinical features (pain intensity, disability, pain catastrophizing, and fear-avoidance beliefs) on trunk postural control.

RESULTS

Forty studies (1,821 participants) were included for the descriptive analysis and 24 studies (1,050 participants) were included for the IPD analysis. IPD meta-analyses revealed three main findings: (a) trunk postural control was worse (higher root mean square displacement [RMSdispl], range, and long-term diffusion; lower mean power frequency) among individuals with than without LBP; (b) trunk postural control deteriorated more (higher RMSdispl, short- and long-term diffusion) among individuals with than without LBP when vision was removed; and (c) older age and higher BMI had greater adverse impacts on trunk postural control (higher short-term diffusion; longer time and distance coordinates of the critical point) among individuals with than without LBP. IPD meta-regressions indicated no associations between the limited LBP clinical features that could be considered and trunk postural control.

CONCLUSION

Trunk postural control appears to be inferior among individuals with LBP, which was indicated by increased seat movements and some evidence of trunk stiffening. These findings are likely explained by delayed or less accurate corrective responses.

SYSTEMATIC REVIEW REGISTRATION

This review has been registered in PROSPERO (registration number: CRD42021124658).

Development and pilot of equine facilitated physical therapy outcome measure tool for chronic low back pain patients

Equine Facilitated Physical Therapy (EFPT) lacks consistent documentation due to being an unconventional physical therapy treatment to chronic low back pain patients (LBP) and lacking rehabilitation outcome measure tools for a stable (equestrian) environment. The objectives were to develop an online evaluation tool as well as to define inter- and intra-rater reliability to validate the outcome measurement tool "Evaluation of maintaining sitting position (on a horse) and walking (short distances)" designed for LBP patients in EFPT". A total of 48 movement related functions (n = 48), were derived from the International Classification of Functioning (ICF) and organized to an online evaluation tool. Depending on the state of validation two to six (2-6) raters scored randomized patient (n = 22) video material, recorded during a 12-week EFPT intervention, with the designed tool. Inter-rater agreement level between the experts reached good (α = 87) reliability for the scoring of the items and calculated per patient excellent (α = 100). Intra-rater reliability reached good (α = 87) and per patient good (α = 80) repeatability. For the healthy adults the reliability between raters reached acceptable (α = 72) levels and per rated excellent (α = 100). The developed assessment tool was found satisfactory to fulfil the requirement for the therapeutic practice. With the use of the tool physical therapist may detect postural changes for LBP patients as outcome report in EFPT. The tool may be used to identify treatment progress and to help design home exercises. The created tool will help to collect similar outcome measures from LBP patients in EFPT and to validate the treatment within industry.

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.

Stereophotogrammetric approaches to multi-segmental kinematics of the thoracolumbar spine: a systematic review

BACKGROUND

Spine disorders are becoming more prevalent in today's ageing society. Motion abnormalities have been linked to the prevalence and recurrence of these disorders. Various protocols exist to measure thoracolumbar spine motion, but a standard multi-segmental approach is still missing. This study aims to systematically evaluate the literature on stereophotogrammetric motion analysis approaches to quantify thoracolumbar spine kinematics in terms of measurement reliability, suitability of protocols for clinical application and clinical significance of the resulting functional assessment.

METHODS

Electronic databases (PubMed, Scopus and ScienceDirect) were searched until February 2022. Studies published in English, investigating the intersegmental kinematics of the thoracolumbar spine using stereophotogrammetric motion analysis were identified. All information relating to measurement reliability; measurement suitability and clinical significance was extracted from the studies identified.

RESULTS

Seventy-four studies met the inclusion criteria. 33% of the studies reported on the repeatability of their measurement. In terms of suitability, only 35% of protocols were deemed suitable for clinical application. The spinous processes of C7, T3, T6, T12, L1, L3 and L5 were the most widely used landmarks. The spine segment definitions were, however, found to be inconsistent among studies. Activities of daily living were the main tasks performed. Comparable results between protocols are however still missing.

CONCLUSION

The literature to date offers various stereophotogrammetric protocols to quantify the multi-segmental motion of the thoracolumbar spine, without a standard guideline being followed. From a clinical point of view, the approaches are still limited. Further research is needed to define a precise motion analysis protocol in terms of segment definition and clinical relevance.

Abdominal wall tension increases using Dynamic Neuromuscular Stabilization principles in different postural positions

BACKGROUND

Intra-abdominal pressure (IAP) is an important mechanism stabilizing the spine and trunk. IAP regulation depends on the coordination of abdominal muscles, diaphragm and pelvic floor muscles.

OBJECTIVE

To determine the differences in abdominal wall tension (AWT) of various postural positions, first without any correction, then after verbal and manual instructions according to Dynamic Neuromuscular Stabilization (DNS) principles.

METHODS

In a cross-sectional observational study, thirty healthy individuals (mean age = 22.73 ± 1.91 years) were fitted with two Ohmbelt sensors contralaterally above the inguinal ligament and in the upper lumbar triangle. AWT was measured during five postural positions: sitting, supine with legs raised, squat, bear and hang position. First, spontaneous AWT was measured, then again after manual and verbal instructions following DNS principles.

RESULTS

AWT increased significantly with DNS instructions compared to spontaneous activation. Both sensors recorded significant increases (p < .01; Cohen's d = -1.13 to -2.06) in all observed postural situations. The increase in activity occurred simultaneously on both sensors, with no significant differences noted in pressure increases between the sensors. The greatest activation for both sensors occurred in the bear position. Significant increases in activity were identified for both sensors in the supine leg raise position and in the bear position compared to spontaneous activation in sitting (p < .001). There were no statistically significant differences (for both sensors) between women and men in any position.

CONCLUSION

The amount of AWT significantly increases after verbal and manual instructions according to DNS. The greatest abdominal wall activation was achieved in the bear position.

Acute effects of game-based biofeedback training on trunk motion in chronic low back pain: a randomized cross-over pilot trial

BACKGROUND

Improving movement control might be a promising treatment goal during chronic non-specific low back pain (CLBP) rehabilitation. The objective of the study is to evaluate the effect of a single bout of game-based real-time feedback intervention on trunk movement in patients with CLBP.

METHODS

Thirteen CLBP patients (8female;41 ± 16 years;173 ± 10 cm;78 ± 22 kg) were included in this randomized cross-over pilot trial. During one laboratory session (2 h), participants performed three identical measurements on trunk movement all including: first, maximum angle of lateral flexion was assessed. Secondly, a target trunk lateral flexion (angle: 20°) was performed. Main outcome was maximum angle ([°]; MA). Secondary outcomes were deviation [°] from the target angle (angle reproduction; AR) and MA of the secondary movement planes (rotation; extension/flexion) during lateral flexion. The outcomes were assessed by an optical 3D-motion-capture-system (2-segment-trunk-model). The measurements were separated by 12-min of intervention and/or resting (randomly). The intervention involved a sensor-based trunk exergame (guiding an avatar through virtual worlds). After carryover effect-analysis, pre-to-post intervention data were pooled between the two sequences followed by analyses of variances (paired t-test).

RESULTS

No significant change from pre to post intervention for MA or AR for any segment occurred for the main movement plane, lateral flexion (p > .05). The upper trunk segment showed a significant decrease of the MA for trunk extension/flexion from pre to post intervention ((4.4° ± 4.4° (95% CI 7.06-1.75)/3.5° ± 1.29° (95% CI 6.22-0.80); p = 0.02, d = 0.20).

CONCLUSIONS

A single bout of game-based real-time feedback intervention lead to changes in the secondary movement planes indicating reduced evasive motion during trunk movement.

TRIAL REGISTRATION NO

DRKS00029765 (date of registration 27.07.2022). Retrospectively registered in the German Clinical Trial Register.

Postural control of the trunk in individuals with and without low back pain during unstable sitting: A protocol for a systematic review with an individual participant data meta-analysis

Introduction

Postural control of the trunk is critical for performance of everyday activities and the health of spinal tissues. Although some studies report that individuals with low back pain (LBP) have poorer/compromised postural control than pain-free individuals when sitting on an unstable surface, others do not. Analyses commonly lack the statistical power to evaluate the relevance of features that could impact the performance of postural control, such as sex, age, anthropometrics, pain intensity or disability. This paper outlines a protocol for a systematic review with an individual participant data (IPD) meta-analysis that aims to synthesise the evidence and evaluate differences of postural control measures between individuals with and without LBP during unstable sitting.

Methods and analysis

A systematic review with IPD meta-analysis will be conducted according to PRISMA-IPD guidelines. To identify relevant studies, electronic databases and the reference lists of included articles will be screened. Unstable seat movements are derived from centre of pressure (CoP) data using a force plate or angle of the seat using motion systems/sensors. The comprehensiveness of reporting and methodological quality of included studies will be assessed. Analysis will involve a descriptive analysis to synthesise the findings of all included studies and a quantitative synthesis using two-stage IPD meta-analysis of studies that include both individuals with and without LBP for which IPD set can be obtained from authors. Analyses will include consideration of confounding variables.

Ethics

Exemption from ethical approval was obtained for this review (University of Queensland, ID: 2019003026).

Systematic review registration

PROSPERO ID: CRD42021124658.

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.

Center of pressure displacement due to graded controlled perturbations to the trunk in standing subjects: the force-impulse paradigm

PURPOSE

Many studies have investigated postural reactions (PR) to body-delivered perturbations. However, attention has been focused on the descriptive variables of the PR rather than on the characterization of the perturbation. This study aimed to test the hypothesis that the impulse rather than the force magnitude of the perturbation mostly affects the PR in terms of displacement of the center of foot pressure (ΔCoP).

METHODS

Fourteen healthy young adults (7 males and 7 females) received 2 series of 20 perturbations, delivered to the back in the anterior direction, at mid-scapular level, while standing on a force platform. In one series, the perturbations had the same force magnitude (40 N) but different impulse (range: 2-10 Ns). In the other series, the perturbations had the same impulse (5 Ns) but different force magnitude (20-100 N). A simple model of postural control restricted to the sagittal plane was also developed.

RESULTS

The results showed that ΔCoP and impulse were highly correlated (on average: r = 0.96), while the correlation ΔCoP-force magnitude was poor (r = 0.48) and not statistically significant in most subjects. The normalized response, ΔCoP_n = ΔCoP/I, was independent of the perturbation magnitude in a wide range of force amplitude and impulse and exhibited good repeatability across different sets of stimuli (on average: ICC = 0.88). These results were confirmed by simulations.

CONCLUSION

The present findings support the concept that the magnitude of the applied force alone is a poor descriptor of trunk-delivered perturbations and suggest that the impulse should be considered instead.

Preferred Limb Reaction, Swing and Recovery Step Times between Subjects with and without Chronic Low Back Pain

A compensatory stepping strategy following repeated perturbations may compromise dynamic balance and postural stability. However, there is a lack of study on preferred limb reaction, swing, and step time adjustments. The purpose of this study was to investigate limb reaction, swing, and recovery step times following repeated trip perturbations in individuals with and without non-specific chronic low back pain (LBP). There were 30 subjects with LBP and 50 control subjects who participated in the study. The limb reaction, swing, and recovery step times (s) were measured following treadmill-induced random repeated perturbations (0.12 m/s velocity for 62.5 cm displacement), which caused subjects to move forward for 4.90 s. Both groups demonstrated a significant interaction of repetitions and times (F = 4.39, p = 0.03). Specifically, the recovery step time was significantly shorter in the LBP group during the first trip (t = 2.23, p = 0.03). There was a significant interaction on repetitions and times (F = 6.03, p = 0.02) in the LBP group, and the times were significantly different (F = 45.04, p = 0.001). The initial limb reaction time of the LBP group was significantly correlated with three repeated swing times to avoid falls. The novelty of the first trip tends to enhance a protective strategy implemented by the LBP group. Although limb preference did not demonstrate a significant difference between groups, the LBP group demonstrated shorter recovery step times on their preferred limb initially in order to implement an adaptive strategy to avoid fall injuries following repeated perturbations.

Reliability of measures to characterize lumbar movement patterns, in repeated seated reaching, in a mixed group of participants with and without low-back pain: A test-retest, within- and between session

Literature highlights the need for research on changes in lumbar movement patterns, as potential mechanisms underlying the persistence of low-back pain. Variability and local dynamic stability are frequently used to characterize movement patterns. In view of a lack of information on reliability of these measures, we determined their within- and between-session reliability in repeated seated reaching. Thirty-six participants (21 healthy, 15 LBP) executed three trials of repeated seated reaching on two days. An optical motion capture system recorded 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). Reliability was evaluated using intraclass correlation coefficients (ICC), coefficients of variation (CV) and Bland-Altman plots. Sufficient reliability was defined as an ICC ≥ 0.5 and a CV < 20%. To determine the effect of number of repetitions on reliability, analyses were performed for the first 10, 20, 30, and 40 repetitions of each time series. MeanSD, CyclSD, and the LDE had moderate within-session reliability; meanSD: ICC = 0.60-0.73 (CV = 14-17%); CyclSD: ICC = 0.68 (CV = 17%); LDE: ICC = 0.62 (CV = 5%). Between-session reliability was somewhat lower; meanSD: ICC = 0.44-0.73 (CV = 17-19%); CyclSD: ICC = 0.45-0.56 (CV = 19-22%); LDE: ICC = 0.25-0.54 (CV = 5-6%). MeanSD, CyclSD and the LDE are sufficiently reliable to assess lumbar movement patterns in single-session experiments, and at best sufficiently reliable in multi-session experiments. Within-session, a plateau in reliability appears to be reached at 40 repetitions for meanSD (flexion-extension), meanSD (axial-rotation) and CyclSD.

Adaptive trunk sway velocities following repeated perturbations in subjects with and without low back pain

Faster trunk motions could be a strategy to prevent loss of balance and fall injuries due to unexpected perturbations. However, it is unclear how trunk sway velocities can be compensated during stepping in subjects with low back pain (LBP). The purpose of this study was to investigate lower limb reaction, swing, and step times, as well as trunk sway velocities at heel strike and toe-off, following repeated step perturbations between subjects with and without LBP. There were 30 subjects with LBP and 42 control subjects who were exposed to treadmill-induced perturbations at a velocity of 0.12 m/sec for 0.62 m. The treadmill-induced steps caused subjects to walk forward for 4.90 sec after the perturbation. The groups demonstrated significant interactions on the lower limb reaction times and on the number of repeated perturbations (F = 4.83, p = 0.03) due to a decreased step time at the first perturbation (t = 2.52, p = 0.01) in the LBP group. For the trunk sway velocities, the repeated perturbations demonstrated a significant interaction between groups (F = 4.65, p = 0.03). This adaptive trunk strategy for gait stability increased step times with repeated perturbations in the LBP group. The group interactions on the trunk sway velocities also indicated a possible somatosensory integration for step time adjustments to avoid potential fall hazards. This adaptive response with repeated step perturbations could result in compensatory trunk sway for gait stability.

Effect of whole body vibration on the electromyographic activity of core stabilizer muscles: WBV ON CORE STABILIZER MUSCLES

OBJECTIVE

To analyze the effects of whole body vibration on electromyographic activity of the core muscles.

METHODS

This is an observational cross-sectional study composed of 30 males who practice physical activity. The amplitude of the electromyographic activation (Root Mean Square - RMS) of the rectus abdominis, external oblique, longissimus thoracis, multifidus muscles were evaluated during supine bridge, side plank and frontal plank exercises, performed with and without vibration (frequency: 50 Hz and amplitude: 4 mm). A significance level of 5% was assigned for all analyzes.

RESULTS

Whole body vibration did not alter the amplitude of electromyographic activity for any of the evaluated muscle groups, showing no difference between the conditions with and without vibration during the performance of the proposed exercises.

CONCLUSION

Under the conditions analyzed in this study, the vibrating platform does not change the activation amplitude of core muscles, suggesting that the use of whole body vibration is not necessary as an additional method to increase muscle activity during stabilization exercises in healthy men.

Linearity and repeatability of postural responses in relation to peak force and impulse of manually delivered perturbations: a preliminary study

PURPOSE

Postural reactions (PR) of standing subjects have been mostly investigated in response to platform displacements or body perturbations of fixed magnitude. The objective of this study was to investigate the relationship between PR and the peak force and impulse of the perturbation.

METHODS

In ten healthy young men, standing balance was challenged by anteriorly directed perturbations (peak force: 20-60 N) delivered to the back, at the lumbar (L) or inter-scapular (IS) level, by means of a manual perturbator equipped with a force sensor. Postural reactions as expressed by the displacement of the center of pressure (CoP) were recorded using a force platform. Two sets of 20 randomly ordered perturbations (10 to each site) were delivered in two separate testing sessions.

RESULTS

The magnitude of CoP response (∆CoP) was better correlated with the impulse (I) than with the peak force of the perturbation. The normalized response, ∆CoP_n = ∆CoP/I, exhibited good reliability (ICCs of 0.93 for IS and 0.82 for L), was higher with IS than with L perturbations (p < 0.01), and was significantly correlated with the latency of CoP response: r = 0.69 and 0.71 for IS and L, respectively.

CONCLUSION

These preliminary findings support the concept that manually delivered perturbations can be used to reliably assess individual PR and that ∆CoP_n may effectively express a relevant aspect of postural control.

Hypogravity reduces trunk admittance and lumbar muscle activation in response to external perturbations

Reduced paraspinal muscle size and flattening of spinal curvatures have been documented after spaceflight. Assessment of trunk adaptations to hypogravity can contribute to development of specific countermeasures. In this study, parabolic flights were used to investigate spinal curvature and muscle responses to hypogravity. Data from five trials at 0.25 g, 0.50 g, and 0.75 g were recorded from six participants positioned in a kneeling-seated position. During the first two trials, participants maintained a normal, upright posture. In the last three trials, small-amplitude perturbations were delivered in the anterior direction at the T₁₀ level. Spinal curvature was estimated with motion capture cameras. Trunk displacement and contact force between the actuator and participant were recorded. Muscle activity responses were collected by intramuscular electromyography (iEMG) of the deep and superficial lumbar multifidus, iliocostalis lumborum, longissimus thoracis, quadratus lumborum, transversus abdominis, obliquus internus, and obliquus externus muscles. The root mean square iEMG and the average spinal angles were calculated. Trunk admittance and muscle responses to perturbations were calculated as closed-loop frequency-response functions. Compared with 0.75 g, 0.25 g resulted in lower activation of the longissimus thoracis (P = 0.002); lower responses of the superficial multifidus at low frequencies (P = 0.043); lower responses of the superficial multifidus (P = 0.029) and iliocostalis lumborum (P = 0.043); lower trunk admittance (P = 0.037) at intermediate frequencies; and stronger responses of the transversus abdominis at higher frequencies (P = 0.032). These findings indicate that exposure to hypogravity reduces trunk admittance, partially compensated by weaker stabilizing contributions of the paraspinal muscles and coinciding with an apparent increase of deep abdominal muscle activity.NEW & NOTEWORTHY This study presents for the first time novel insights into the adaptations to hypogravity of spinal curvatures, trunk stiffness, and paraspinal muscle activity. We showed that exposure to hypogravity reduces the displacement of the trunk by an applied perturbation, partially compensated by weaker stabilizing contributions of the paraspinal muscles and concomitant increase in abdominal muscle responses. These findings may have relevance for future recommendations for planetary surface explorations.

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.

Biarticular muscles are most responsive to upper-body pitch perturbations in human standing

Balancing the upper body is pivotal for upright and efficient gait. While models have identified potentially useful characteristics of biarticular thigh muscles for postural control of the upper body, experimental evidence for their specific role is lacking. Based on theoretical findings, we hypothesised that biarticular muscle activity would increase strongly in response to upper-body perturbations. To test this hypothesis, we used a novel Angular Momentum Perturbator (AMP) that, in contrast to existing methods, perturbs the upper-body posture with only minimal effect on Centre of Mass (CoM) excursions. The impulse-like AMP torques applied to the trunk of subjects resulted in upper-body pitch deflections of up to 17° with only small CoM excursions below 2 cm. Biarticular thigh muscles (biceps femoris long head and rectus femoris) showed the strongest increase in muscular activity (mid- and long-latency reflexes, starting 100 ms after perturbation onset) of all eight measured leg muscles which highlights the importance of biarticular muscles for restoring upper-body balance. These insights could be used for improving technological aids like rehabilitation or assistive devices, and the effectiveness of physical training for fall prevention e.g. for elderly people.

Trunk peak torque, muscle activation pattern and sudden loading compensation in adolescent athletes with back pain

OBJECTIVE

To evaluate trunk peak torque and muscle activation pattern during isokinetic and sudden trunk loading (STL) between adolescent athletes with/without back pain.

METHODS

Nine adolescent athletes with back pain (BP) (m/f 2/7; 15.6 ± 1.2 y; 177 ± 9 cm; 67 ± 13 kg; 22.5 ± 9.8 h/week) and nine matched controls (m/f 2/7; 15.7 ± 1.4 y; 177 ± 12 cm; 65 ± 9 kg; 16.5 ± 8.0 h/week training) were included. Trunk strength in rotation and flexion/extension was assessed. Sudden trunk loading was measured during eccentric extension and rotation (30∘/s) with additional perturbation. Trunk muscle activity was measured using a 12 lead-EMG (electromyography). Main outcome measures were peak torque [Nm] and MVC normalized EMG-amplitudes (RMS [%]) for each muscle. Additionally, the mean EMG-RMS for four areas of the trunk was calculated (right/left ventral, right/left dorsal).

RESULTS

Back pain showed lower trunk peak torque for all conditions in extension/flexion, but not for rotation. EMG amplitudes were increased for BP athletes with statistical significant differences for dorsal muscles in rotation and extension (p< 0.0042), not for ventral muscles in flexion.

CONCLUSIONS

The evaluation of strength and muscle activity in isokinetic and sudden trunk loading presents altered trunk function in adolescent back pain athletes. Training interventions focusing on trunk strength and muscular activation pattern appears reasonable.

Compensatory strategy between trunk-hip kinematics and reaction time following slip perturbation between subjects with and without chronic low back pain

Compensatory trunk and hip motions following slip perturbations may compromise the control of lumbopelvic movement. However, it is unclear how postural integration of the trunk and hips can be transferred to treadmill-induced slip perturbations in subjects with chronic low back pain (LBP). The purpose of this study was to investigate trunk reaction times and three-dimensional trunk-hip angle changes following a slip perturbation (duration: 0.12 sec, velocity: 1.37 m/sec, displacement: 8.22 cm) with a handheld task between subjects with and without chronic LBP. There were 23 subjects with LBP and 33 control subjects who participated in the study. The trunk reaction time was not significantly different between groups. However, the three-dimensional trunk-hip angle changes were significantly different following the perturbation. There were significant interactions between the body regions and three-dimensional angles between groups. There was a negative correlation between reaction time and trunk flexion in the LBP group. Overall, the LBP group demonstrated significantly reduced trunk flexion, which might be associated with reduced adaptability or a possible fear of avoidance strategy. Clinicians need to consider compensatory strategies to improve trunk flexibility following slip perturbations in subjects with chronic LBP. Mini abstract: Trunk reaction time and three-dimensional trunk-hip motions were compared between subjects with and without chronic low back pain (LBP). The control group demonstrated greater trunk flexion; however, the LBP group reduced trunk flexion to protect against further injuries following the novelty of the slip perturbation.

Sensorimotor control of the trunk in sitting sway referencing

We developed a sway-referenced system for sitting to highlight the role of vestibular and visual contributions to trunk control. Motor control was investigated by measuring trunk kinematics in the frontal plane while manipulating visual availability and introducing a concurrent cognitive task. We examined motor learning on three timescales (within the same trial, minutes), within the same test session (1 h), and between sessions (1 wk). Posture sway was analyzed through time-based measures [root mean square (RMS) sway and RMS velocity], frequency-based measures (amplitude spectra), and parameterized feedback modeling. We found that posture differed in both magnitude and frequency distribution during sway referencing compared with quiet sitting. Modeling indicated that sway referencing caused greater uncertainty/noise in sensory feedback and motor outputs. Sway referencing was also associated with lower active stiffness and damping model parameters. The influence of vision and a cognitive task was more apparent during sway referencing compared with quiet sitting. Short-term learning was reflected by reduced RMS velocity in quiet sitting immediately following sway referencing. Longer term learning was evident from one week to the next, with a 23% decrease in RMS sway and 9% decrease in RMS velocity. These changes occurred predominantly during cognitive tests at lower frequencies and were associated with lower sensory noise and higher stiffness and integral gains in the model. With the findings taken together, the sitting sway-referenced test elicited neural changes consistent with optimal integration and sensory reweighting, similar to standing, and should be a valuable tool to closely examine sensorimotor control of the trunk. NEW & NOTEWORTHY We developed the first sway-referenced system for sitting to highlight the role of vestibular and visual contributions to trunk control. A parametric feedback model explained sensorimotor control and motor learning in the task with and between two test sessions. The sitting sway-referenced test elicited neural changes consistent with optimal integration and sensory reweighting, similar to standing, and should be a valuable tool to closely examine sensorimotor control of the trunk.

Trunk sway response to consecutive slip perturbations between subjects with and without recurrent low back pain

BACKGROUND

Trunk sway responses following perturbations are critical to develop adequate prevention strategies. It is unclear how postural responses with a handheld task can validly be transferred to treadmill-induced slip perturbations in subjects with recurrent low back pain (LBP).

OBJECTIVE

To compare trunk sway angle, velocity, and reaction time following treadmill-induced perturbations while subjects with and without LBP held a tray.

DESIGN

Cross-sectional study.

METHODS

There were 30 subjects with LBP and 50 control subjects who participated in the study. Each participant stood on the treadmill while he/she held a tray to produce a functional task. Three levels of consecutive slips were introduced based on the specific duration, velocity, and displacement.

RESULTS

The trunk extension angle was significantly different (F = 4.22, p = 0.04) and demonstrated a significant interaction with groups and levels of perturbation (F = 6.83, p = 0.01). However, the reaction time was not significantly different based on the levels of perturbation (F = 0.43, p = 0.51). The LBP group increased trunk extension only at level 1 slip perturbation (t = 2.86, p = 0.005).

CONCLUSION

The increased trunk extension following the first perturbation indicated a delay in adjusting trunk stability in the LBP group. However, there was no group difference with higher magnitudes of perturbations. These results indicated that the LBP group was able to minimize trunk sway with higher perturbations following the first perturbation.

Trunk Reaction Time and Kinematic Changes Following Slip Perturbations in Subjects with Recurrent Low Back Pain

Postural responses following slip perturbations are critical to fall prevention strategies. It is unclear how postural reactions with a handheld task can validly be transferred to treadmill-induced slip perturbations in subjects with recurrent low back pain (LBP). The purpose of this study was to investigate trunk reaction times and trunk flexion angle as well as velocity following the slips between subjects with and without LBP. There were 29 subjects with LBP and 40 control subjects who participated in the study. Three levels of consecutive treadmill-induced slip perturbations were introduced at level 1 (duration: 0.10 s, velocity: 0.24 m/s, displacement: 1.20 cm), level 2 (0.12 s, 0.72 m/s, 4.32 cm), and level 3 (0.12 s, 1.37 m/s, 8.22 cm). The trunk reaction time, swing/step times, and trunk flexion angle as well as velocity at heel strike/toe-off were compared between the groups. There were significantly longer trunk reaction times (t = - 2.03, p = 0.04), swing times (t = - 2.63, p = 0.01), and step times (t = - 2.53, p = 0.01) in the LBP group at the level 1 slip perturbation. The groups demonstrated a significant interaction between the levels and trunk flexion angles (F = 4.72, p = 0.03), but there was no interaction between the levels and trunk flexion velocities (F = 0.07, p = 0.79). The LBP group demonstrated longer reaction times at the level 1 perturbation due to a possible pain recurrence. However, this compensatory tolerance was limited at the level 3 perturbation due to increased trunk flexion angle at heel strike and toe-off in the LBP group. Clinicians may consider a compensatory strategy to improve reaction time and minimize trunk flexion following slip perturbations in patients with LBP.

Evidence of splinting in low back pain? A systematic review of perturbation studies

PURPOSE

The purpose of this systematic review was to assess whether LBP patients demonstrate signs of splinting by evaluating the reactions to unexpected mechanical perturbations in terms of (1) trunk muscle activity, (2) kinetic and (3) kinematic trunk responses and (4) estimated mechanical properties of the trunk.

METHODS

The literature was systematically reviewed to identify studies that compared responses to mechanical trunk perturbations between LBP patients and healthy controls in terms of muscle activation, kinematics, kinetics, and/or mechanical properties. If more than four studies reported an outcome, the results of these studies were pooled.

RESULTS

Nineteen studies were included, of which sixteen reported muscle activation, five kinematic responses, two kinetic responses, and two estimated mechanical trunk properties. We found evidence of a longer response time of muscle activation, which would be in line with splinting behaviour in LBP. No signs of splinting behaviour were found in any of the other outcome measures.

CONCLUSIONS

We conclude that there is currently no convincing evidence for the presence of splinting behaviour in LBP patients, because we found no indications for splinting in terms of kinetic and kinematic responses to perturbation and derived mechanical properties of the trunk. Consistent evidence on delayed onsets of muscle activation in response to perturbations was found, but this may have other causes than splinting behaviour.

Trunk Muscle Activity during Drop Jump Performance in Adolescent Athletes with Back Pain

In the context of back pain, great emphasis has been placed on the importance of trunk stability, especially in situations requiring compensation of repetitive, intense loading induced during high-performance activities, e.g., jumping or landing. This study aims to evaluate trunk muscle activity during drop jump in adolescent athletes with back pain (BP) compared to athletes without back pain (NBP). Eleven adolescent athletes suffering back pain (BP: m/f: n = 4/7; 15.9 ± 1.3 y; 176 ± 11 cm; 68 ± 11 kg; 12.4 ± 10.5 h/we training) and 11 matched athletes without back pain (NBP: m/f: n = 4/7; 15.5 ± 1.3 y; 174 ± 7 cm; 67 ± 8 kg; 14.9 ± 9.5 h/we training) were evaluated. Subjects conducted 3 drop jumps onto a force plate (ground reaction force). Bilateral 12-lead SEMG (surface Electromyography) was applied to assess trunk muscle activity. Ground contact time [ms], maximum vertical jump force [N], jump time [ms] and the jump performance index [m/s] were calculated for drop jumps. SEMG amplitudes (RMS: root mean square [%]) for all 12 single muscles were normalized to MIVC (maximum isometric voluntary contraction) and analyzed in 4 time windows (100 ms pre- and 200 ms post-initial ground contact, 100 ms pre- and 200 ms post-landing) as outcome variables. In addition, muscles were grouped and analyzed in ventral and dorsal muscles, as well as straight and transverse trunk muscles. Drop jump ground reaction force variables did not differ between NBP and BP (p > 0.05). Mm obliquus externus and internus abdominis presented higher SEMG amplitudes (1.3–1.9-fold) for BP (p < 0.05). Mm rectus abdominis, erector spinae thoracic/lumbar and latissimus dorsi did not differ (p > 0.05). The muscle group analysis over the whole jumping cycle showed statistically significantly higher SEMG amplitudes for BP in the ventral (p = 0.031) and transverse muscles (p = 0.020) compared to NBP. Higher activity of transverse, but not straight, trunk muscles might indicate a specific compensation strategy to support trunk stability in athletes with back pain during drop jumps. Therefore, exercises favoring the transverse trunk muscles could be recommended for back pain treatment.