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

With low back pain (LBP), remodelling of the lumbar soft tissues involves both trunk muscles and neighbouring passive connective tissues. The aim of the present study was to compare three quantitative measures of these tissues, using ultrasound imaging (USI), among healthy controls and individuals with LBP.USI measures from 30 healthy subjects and 34 patients with non-acute LBP were compared between groups and sexes. The measures employed were (1) lumbar multifidus echogenicity (fatty/fibrosis infiltration) at three vertebral levels; (2) posterior layer thickness of the thoracolumbar fascia, and (3) thickness of the perimuscular tissues surrounding the external oblique, internal oblique and transversus abdominis (TrA).USI measures of (1) multifidus echogenicity showed statistically significant changes between vertebral levels and sexes (females males; p = 0.02); (2) differences in thoracolumbar fascia thickness approached statistical significance between groups (LBP controls; p = 0.09) and sexes (femalesmales; p = 0.07); and (3) perimuscular tissue surrounding the TrA was significantly thinner (p ≤ 0.001) in patients with LBP compared to controls.The thinner perimuscular tissues surrounding the TrA in patients with LBP is a new finding, concurring with previous findings with regard to the lower activation of this deep muscle as well as more recent findings on other perimuscular tissue.Overall, USI measures were sensitive to different potential changes (pain status, sex, vertebral level), and this is useful in studying the remodelling of various soft tissues of the trunk.

Objective The primary aim was to test the construct validity of a surface electromyography (EMG) measurement protocol, indirectly assessing the effects of anti-vibration (AV) gloves on activities of the forearm muscles. Background AV gloves impose a relatively higher grip demand and thus a higher risk for musculoskeletal disorders. Consequently, activities of the forearm muscles should be considered when assessing AV glove performance. Method Effects of AV gloves on activities of the forearm muscles (ECR: extensor carpi radialis longus; ED: extensor digitorum; FCR: flexor carpi radialis; FDS: flexor digitorum superficialis) were measured via EMG, while gripping a handle with two grip force levels. Fifteen subjects participated with 11 glove conditions, including one with bare hand. Results Activities of ECR, FCR, mean of ECR and FCR (ECR_FCR), and mean of all four muscles were sensitive to wearing gloves. Compared with bare hand, combined ECR_FCR activities increased by 22%–78% (mean = 48%, SD = 28%) with gloves. The correlation coefficient ( r) of ECR_FCR activities with glove thickness and manual dexterity scores were 0.74 ( p < .05) and 0.90 ( p < .001), respectively. Conclusions A refined EMG methodology was the most sensitive to AV gloves with specific forearm muscles (ECR and FCR) and the 50-N handgrip force. Its construct validity was further substantiated by correlations with glove thickness and manual dexterity. Application Assessment of the effect of AV gloves on activities of the forearm muscles can yield design guidance for AV gloves to reduce grip exertion by the gloved hand.

Low back pain (LBP) remains one of the most common and incapacitating health conditions worldwide. Clinical guidelines recommend exercise programs after the acute phase, but clinical effects are modest when assessed at a population level. Research needs to determine who is likely to benefit from specific exercise interventions, based on clinical presentation. This study aimed to derive clinical prediction rules (CPRs) for treatment success, using a lumbar stabilization exercise program (LSEP), at the end of treatment and at six-month follow-up. The eight-week LSEP, including clinical sessions and home exercises, was completed by 110 participants with non-acute LBP, with 100 retained at the six-month follow-up. Physical (lumbar segmental instability, motor control impairments, posture and range of motion, trunk muscle endurance and physical performance tests) and psychological (related to fear-avoidance and home-exercise adherence) measures were collected at a baseline clinical exam. Multivariate logistic regression models were used to predict clinical success, as defined by ≥50% decrease in the Oswestry Disability Index. CPRs were derived for success at program completion (T8) and six-month follow-up (T34), negotiating between predictive ability and clinical usability. The chosen CPRs contained four (T8) and three (T34) clinical tests, all theoretically related to spinal instability, making these CPRs specific to the treatment provided (LSEP). The chosen CPRs provided a positive likelihood ratio of 17.9 (T8) and 8.2 (T34), when two or more tests were positive. When applying these CPRs, the probability of treatment success rose from 49% to 96% at T8 and from 53% to 92% at T34. These results support the further development of these CPRs by proceeding to the validation stage.

Various interpretations and parameters have been proposed to assess spinal stability such as antagonist muscle coactivity, trunk stiffness and spinal buckling load; however, the correlation between these parameters remains unknown. We evaluated spinal stability during different tasks while changing the external moment and load height and investigated likely relationships between different EMG- and model-based parameters (e.g., EMG coactivity ratio, trunk stiffness, force coactivity ratio) and stability margins. EMG and kinematics of 40 young healthy subjects were recorded during various quasi-static tasks. Muscle forces, trunk stiffness and stability margins were calculated by a nonlinear subject-specific EMG-assisted-optimization musculoskeletal model of the trunk. The load elevation and external moment increased muscle activities and trunk stiffness while all stability margins (i.e., buckling loads) decreased. The force coactivity ratio was strongly correlated with the hand-load stability margin (i.e., additional weight in hands to initiate instability

Conventional electromyography-driven (EMG) musculoskeletal models are calibrated during maximum voluntary contraction (MVC) tasks, but individuals with low back pain cannot perform unbiased MVCs. To address this issue, EMG-driven models can be calibrated in submaximal tasks. However, the effects of maximal (when data points include the maximum contraction) and submaximal calibration techniques on model outputs (e.g., muscle forces, spinal loads) remain yet unknown. We calibrated a subject-specific EMG-driven model, using maximal/submaximal isometric contractions, and simulated different independent tasks. Both approaches satisfactorily predicted external moments (Pearson's correlation ∼ 0.75; relative error = 44%), and removing calibration tasks under axial torques markedly improved the model performance (Pearson's correlation ∼ 0.92; relative error ∼ 28%). Unlike individual muscle forces, gross (aggregate) model outputs (i.e., spinal loads, stability index, and sum of abdominal/back muscle forces) estimated from maximal and submaximal calibration techniques were highly correlated (r 0.78). Submaximal calibration method overestimated spinal loads (6% in average) and abdominal muscle forces (11% in average). Individual muscle forces estimated from maximal and submaximal approaches were substantially different; however, gross model outputs (especially internal loads and stability index) remained highly correlated with small to moderate relative differences; therefore, the submaximal calibration technique can be considered as an alternative to the conventional maximal calibration approach.

Background Numerous investigations have revealed significant relations between pain and fatigue in individuals with persistent pain conditions. However, the direction of influence between pain and fatigue remains unclear. Shortcomings of design and analytic approaches used in previous research limit the nature of conclusions that can be drawn about possible causal or directional relations between pain and fatigue. The present study investigated the temporal relation between changes in pain and changes in fatigue in individuals with musculoskeletal pain enrolled in a 10-week behavioral activation intervention. On the basis of previous findings, it was hypothesized that analyses would support a bi-directional relation between pain and fatigue. Methods The study sample consisted of 104 individuals with chronic musculoskeletal pain participating in a 10-week standardized rehabilitation intervention. Measures of pain intensity and fatigue were completed pre-, mid-, and post-treatment. The three-wave data panel permitted examination of the direction of influence between pain and fatigue through the course of the intervention. A random-intercept cross-lagged panel model (RI-CLPM) was used to examine the temporal relation between pain and fatigue. Results Consistent with previous research, cross-sectional analyses of pre-treatment data revealed significant correlations between measures of pain and fatigue. Significant reductions in pain and fatigue were observed through the course of treatment (d = 0.33 and d = 0.66, p p = 0.02; mid to post-treatment β = 0.36, p = 0.001); however, fatigue did not predict later pain severity. Conclusions Discussion addresses the processes that might underlie the temporal relation between pain and fatigue. Clinical implications of the findings are also discussed.

Purpose Individual psychosocial factors are crucial in the return to work (RTW) process of workers with musculoskeletal disorders (MSDs) and common mental disorders (CMDs). However, the quality and validity of the questionnaires used to measure these factors have rarely been investigated. The present systematic search and literature review aims at identifying, categorizing, and evaluating the questionnaires (measurement tools) used to measure individual psychosocial factors related to the perception of the personal condition and motivation to RTW that are predictive of successful RTW among workers with MSDs or CMDs. Methods Through a systematic search on PubMed, Web of Science, and PsycINFO library databases and grey literature, we identified the individual psychosocial factors predictive of successful RTW among these workers. Then, we retrieved the questionnaires used to measure these factors. Finally, we searched for articles validating these questionnaires to describe them exhaustively from a psychometric and practical point of view. Results: The review included 76 studies from an initial pool of 2263 articles. Three common significant predictors of RTW after MSDs and CMDs emerged (i.e., RTW expectations, RTW self-efficacy, and work ability), two significant predictors of RTW after MSDs only (i.e., work involvement and the self-perceived connection between health and job), and two significant predictors of RTW after CMDs only (i.e., optimism and pessimism). We analyzed 30 questionnaires, including eight multiple-item scales and 22 single-item measures. Based on their psychometric and practical properties, we evaluated one of the eight multiple-item scales as questionable and five as excellent. Conclusions: With some exceptions (i.e., self-efficacy), the tools used to measure individual psychosocial factors show moderate to considerable room for improvement. Electronic supplementary material The online version of this article (10.1007/s10926-020-09935-6) contains supplementary material, which is available to authorized users.

Recently remodeling of lumbar soft tissues has received increased research attention. However, the major determinants that influence remodeling need to be elucidated in order to understand the impact of different rehabilitation modalities on tissue remodeling. The main aim of this study was to explore the between-subject variance of different measures of lumbar soft tissues quantified with rehabilitative ultrasound imaging (RUSI). RUSI measures (n = 8) were collected from 30 subjects without and 34 patients with LBP: (1) lumbar multifidus (LM) echogenicity (fatty infiltration/fibrosis) at three vertebral levels (L3/L4, L4/L5 and L5/S1) (n = 3); (2) posterior layer thickness of the thoracolumbar fascia (n = 1); and (3) thickness of the fasciae surrounding the external oblique (EO), internal oblique (IO), and transversus abdominis (TrA) (n = 4). Forward stepwise multivariate regression modeling was conducted with these RUSI measures as dependent variables, using the following independent variables as potential determinants: age, sex, the presence of LBP, body size/composition characteristics (height, weight, trunk length, subcutaneous tissue thickness over the abdominal, and LM muscles), trunk muscle function (or activation) as determined with the percent thickness change of LM, EO, IO, and TrA muscles during a standardized effort (RUSI measures), and physical activity level during sport and leisure activities as estimated with a self-report questionnaire. Two or three statistically significant predictors (or determinants) were selected in the regression model of each RUSI measure (n = 8 models), accounting for 26-64% of their total variance. The subcutaneous tissue thickness on the back accounted for 15-30% variance of LM echogenicity measures and thoracolumbar fascia thickness while the subcutaneous tissue thickness over the abdominals accounted for up to 42% variance of the fascia separating the subcutaneous adipose tissues and the EO muscle. The thickness of IO at rest accounted for 13-21% variance of all investigated abdominal fasciae except the fascia separating the subcutaneous adipose tissue and EO. Pain status accounted for 13-18% variance of the anterior and posterior fasciae of the TrA. Age accounted for 11-14% variance of LM echogenicity at all investigated vertebral levels while sex accounted for 15-21% variance of LM echogenicity at L3/L4 and fascia separating subcutaneous adipose tissue and EO muscle. The function (or activation) of EO and LM at L3/L4 accounted for 8-11% variance of the thoracolumbar fascia and fascia separating TrA and intra-abdominal content (TrA posterior fascia), respectively. Finally, the physical activity level during sport activities accounted for 7% variance of the fascia separating the subcutaneous adipose tissues and the EO muscle. These findings suggest that determinants other than body size characteristics may impact the remodeling of lumbar soft tissues, more importantly the subcutaneous adipose tissue deposits (thickness RUSI measures), which are associated with ectopic fat deposition in the LM and in the fasciae that are more closely positioned to the surface. While age, sex, and pain status explain some variability, modifiable factors such as physical activity level as well as trunk muscle thickness and function were involved. Overall, these results suggest that rehabilitation can potentially impact tissue remodeling, particularly in terms of intramuscular and perimuscular adipose tissues.

Introduction Growing interest is being paid to the lumbar multifidus (LM) intramuscular fatty infiltrations and fibrosis that are secondary to low back pain as well to the remodeling of perimuscular connective tissues (fasciae) such as the thoracolumbar fascia and fascia sheets separating the abdominal wall muscles. Magnetic resonance imaging and computed tomography have traditionally been used but rehabilitative ultrasound imaging (RUSI) is much more affordable and practical, which can accelerate research and clinical applications on this topic. The aim of this study was to test the medium-term (8 weeks) test-retest reliability of the corresponding RUSI measures. Methods Thirty-four participants with non-acute LBP and 30 healthy controls performed a RUSI assessment before and after an 8-week time interval. LM echogenicity was quantified to assess fatty infiltrations and fibrosis while fasciae were quantified with thickness measures. Relative and absolute reliability were estimated using the generalizability theory as a framework, allowing to partition the different sources of error. Results Overall, the reliability findings were quite acceptable, with negligible systematic effects. Excellent relative reliability was reached in half of the investigated RUSI measures, particularly when averaging measures across trials. However, neither relative, nor absolute reliability results support the use of these RUSI measurements on an individual basis (e.g. clinical applications) but they are useful on a group basis (e.g. research applications). Discussion The different sources of error were distributed unequally across RUSI measures, pointing to different measurement strategies to mitigate the underlying errors. Conclusions The use of the generalizability theory allowed identifying the sources of error of the different RUSI measures. For each category of measure, depending of the distribution of errors, it was possible to recommend specific measurement strategies to mitigate them.

Background Lumbar stabilization exercise programs (LSEPs) act positively on clinical outcome measures in patients with low back pain (LBP), but the underlying mechanisms are not well understood. Among the various neuromuscular mechanisms, a good candidate is better activation of the abdominal wall, as measured with rehabilitative ultrasound imaging (RUSI). Objectives To determine whether RUSI measures are (1) sensitive to LBP status and treatment (LSEP) and (2) correlate with clinical outcomes following the LSEP. Design An exploratory one-arm clinical trial with healthy participants as a control group. Setting LSEP was delivered in a clinical setting; outcomes were measured in a laboratory setting. Participants Thirty-one patients with nonacute LBP and 30 healthy controls. Methods Outcome measures were performed before and after an 8-week LSEP in patients with LBP, and with the same time interval for control participants to compare with patients at baseline. Main outcome measurements Pain, disability, as well as static (at rest) and dynamic (percent thickness change) RUSI measures for abdominal muscles (transversus abdominis, internal oblique [IO], and external oblique [EO]). Results Patients did not produce systematic changes in RUSI measures relative to controls, even if patients had significant improvement in pain and disability. However, the correlational analyses between the absolute change (pre- to post-LSEP) (1) of EO and IO thickness (in mm) at rest (bilaterally), and (2) in pain following the LSEP were significant and consistent (range: .36-.45) in patients. Conclusions Although positive clinical improvements were observed following LSEP, there were minimal systematic changes in RUSI measures, likely because patients were not different from controls at baseline. Correlational analyses, however, indicated that greater reductions in pain were associated with reduced thickness of the EO and IO following the LSEP, suggesting the presence of some heterogeneity (or clinical subgroups) among the patients. Level of evidence II.

Purpose The objective of this study was to identify organizational factors that are predictive of return-to-work (RTW) among workers with musculoskeletal (MSD) and common mental disorders (CMD), and to subsequently catalogue and characterize the questionnaires (tools) used to measure them. Methods A systematic search on PubMed, Web of Science and PsycINFO library databases and grey literature was conducted. First, a list of organizational factors predictive of RTW for the two populations considered was built. Second, the questionnaires used to measure these factors were retrieved. Third, we looked in the scientific literature for studies on the psychometric properties and practical relevance of these questionnaires. Results Among the factors retained, perceived social support from supervisor and co-workers, work accommodations, and job strain were identified as common RTW factors. Other risk/protective factors, and associated tools, specifically targeting either people with MSD or CMD were also analysed. Conclusions Researchers and practitioners are often uncertain of which tools to use to measure organizational factors which can facilitate or hinder RTW. This study provides an evaluation of the tools measuring predictive organizational RTW factors in people with MSD and CMD. The identified tools can be used in everyday practice and/or research.

Low back pain (LBP) has been previously associated with delayed anticipatory postural adjustments (APAs) determined by trunk muscle activation. Lumbar stabilization exercise programs (LSEP) for patients with LBP may restore the trunk neuromuscular control of the lumbar spine, and normalize APAs. This exploratory study aimed at testing the reliability of EMG and kinematics-based postural adjustment measures over an 8-week interval, assessing their sensitivity to LBP status and treatment and examining their relationship with clinical outcomes.Muscle activation of 10 trunk muscles, using surface electromyography (EMG), and lumbar angular kinematics were recorded during a rapid arm-raising/lowering task. Patients with LBP were tested before and after an 8-week LSEP. Healthy controls receiving no treatment were assessed over the same interval to determine the reliability of the measures and act as a control group at baseline. Muscle activation onsets and reactive range of motion, range of velocities and accelerations were assessed for between group differences at baseline and pre- to post-treatment effects within patients with LBP using t-tests. Correlations between these dependent variables and the change of clinical outcomes (pain, disability) over treatment were also explored.Kinematic-based measures showed comparable reliability to EMG-based measures. Between-group differences were found in lumbar lateral flexion ROM at baseline (patients controls). In the patients with LBP, lateral flexion velocity and acceleration significantly increased following the LSEP. Correlational analyses revealed that lumbar angular kinematics were more sensitive to changes in pain intensity following the LSEP compared to EMG measures. These findings are interpreted in from the perspective of guarding behaviors and lumbar stability hypotheses.Future clinical trials are needed to target patients with and without delayed APAs at baseline and to explore the sensitivity of different outcome measures related to APAs. Different tasks more challenging to postural stability may need to be explored to more effectively reveal APA dysfunction.

Background Wearing a lumbosacral orthosis (LSO) is known to influence spine mechanics, but less is known about how LSOs affect motor control. Whether the use of a LSO can negatively affect motor control of the lumbar spine is still under debate. Objective The current study examined the immediate effects of two flexible LSOs (extensible and non-extensible) on the anticipatory postural adjustments that prepare the spine for a predictable perturbation. Design A comparative study using a repeated measures design in a laboratory setting. Methods Healthy controls (n = 20) and participants with low back pain (n = 40) performed a rapid arm flexion/extension cycle with and without these LSOs. The latency between the activations of the shoulder and different back (iliocostalis lumborum) and abdominal (rectus abdominis, internal and external obliques) muscles, as measured with surface electromyography, was used as the outcome. Results The effects, which were comparable between groups and between LSOs, were mixed, with some muscles showing significantly (p ˂ 0.05) earlier activation and others showing delayed activation with the use of a LSO, relative to the control condition. The corresponding effect sizes were low to average (Hedges's g range: 0.17–0.48). Conclusions These findings suggest a change in the motor program before task initiation, which might be generalizable to other activities of daily living or work. However, none of the effects were large, making it difficult to provide clear conclusions with regard to their clinical relevance. It remains to be tested whether these immediate adaptations in motor planning can induce long term detrimental effects to the control of lumbar stability.

Tendon integrity can be described using a wide range of biomarkers via specialized analysis software for images recorded by musculoskeletal ultrasonography. This study proposes a minimal biomarker data set to characterize Achilles tendon ultrasound images and to differentiate between symptomatic and asymptomatic Achilles tendon images. Forty-one individuals with unilateral Achilles tendinopathy and 35 healthy controls had their Achilles tendon images recorded bilaterally by ultrasonography in the longitudinal and transverse planes. A set of 22 biomarkers, organized around three dimensions (geometric, composition and texture), were computed in each plane. A symmetry index, reflecting relative side differences, was compared between groups and analyzed through principal component analysis to isolate biomarkers that best explained data variance. A specific minimal data set was identified by linear regression in the longitudinal (mean thickness, echogenicity, variance and homogeneity at 90°) and transverse (mean thickness, echogenicity and mean homogeneity) planes to characterize and differentiate Achilles tendon integrity.

Low-back pain (LBP) has been recognized as the leading cause of disability worldwide. Lumbar instability has been considered as an important mechanism of LBP and one potential contributor to lumbar stability is trunk muscle reflex activity. However, due to the differences in experimental paradigms used to quantify trunk mechanics and trunk reflexes it remains unclear as to what extent the reflex pathway contributes to overall lumbar stability. The goal of this work was to determine to what extent reflexes of various trunk muscles were elicited by the small continuous perturbations normally used to quantify trunk mechanics. Electromyographic (EMG) activity was measured bilaterally from 3 trunk extensor muscles and 3 trunk flexor muscles at four epochs: 25–50ms, 50–75ms, 75–100ms and 100–125ms following each perturbation. Reflex activity was seen in all muscles as 34 of the 48 muscle-epoch combinations showed a significant reflex response to either perturbations in the forward or backward direction. However, the reflex EMG activity did not correlate with mechanical estimates of the reflex response. Thus, even though reflexes are indeed elicited by the small perturbations used to quantify trunk mechanics, their exact contribution to overall lumbar stability remains unknown.

Background Lumbar belts have been shown to increase lumbar stiffness, but it is unclear if this is associated with trunk muscle co-contraction, which would increase the compression on the spine. It has been hypothesized that lumbar belts increase lumbar stiffness by increasing intra-abdominal pressure, which would increase spinal stability without increasing the compressive load on the spine. Methods Trunk muscle activity and lumbar stiffness and damping were measured in healthy and low-back pain subjects during three conditions: no lumbar belt; wearing an extensible lumbar belt; wearing a non-extensible lumbar belt. Muscle activity was measured while subjects performed controlled forward and backward 20° trunk sways. Lumbar stiffness and damping were measured by applying random continuous perturbation to the chest. Findings External oblique activity was decreased when wearing either lumbar belt during all phases of movement, while rectus abdominis and iliocostalis activity were decreased during the phase of movement where the muscles were maximally active while wearing either belt. Trunk stiffness was greatly increased by wearing either belt. There were no consistent differences in either lumbar stiffness or muscle activity between the two belts. Wearing a lumbar belt had little to no effect on damping. There were no group differences in any of the measures between healthy and low-back pain populations. Interpretation The findings are consistent with the hypothesis that lumbar belts can increase spinal stability by increasing intra-abdominal pressure, without any increase in the compressive load on the spine. The findings can also be generalized, for the first time, to subjects with low-back pain.

Two potential interventions for enhancing lumbar stability are to actively increase abdominal muscle activity, either through the abdominal drawing-in maneuver (ADIM) or bracing, and passively increase lumbar stiffness using a lumbosacral orthosis (LSO).To compare the increase in lumbar stiffness after 2 active interventions (ADIM versus bracing) and 1 passive intervention (LSO), and to evaluate the combined effect of active (abdominal bracing) and passive interventions.In this experimental and comparative study, lumbar stiffness, a surrogate measure of lumbar stability, was estimated in 25 healthy individuals during 7 trunk perturbation conditions: (1) control, (2) ADIM, (3) bracing at 5% of right external oblique maximal voluntary activation (5% bracing), (4) bracing at 10% of right external oblique maximal voluntary activation (10% bracing), (5) LSO, (6) LSO plus 5% bracing, and (7) LSO plus 10% bracing. Electromyographic biofeedback of the external oblique was provided on a monitor, while ultrasound was used for the ADIM to ensure a sustained contraction of the transversus abdominis.The ADIM, 5% bracing, and 10% bracing active interventions generated comparable lumbar stiffness. However, considering that bracing can range from 10% to 20%, it may be superior to hollowing, as further estimated with a mixed-effect statistical model. Combining bracing and an LSO resulted in an additive effect on lumbar stiffness.Bracing and ADIM produced comparable lumbar stiffness, as they were performed at the same overall abdominal activation levels (5% and 10% maximal voluntary activation). The independent effects of bracing and LSO raises the possibility of combining these interventions in some circumstances. J Orthop Sports Phys Ther 2019;49(4):262-271. Epub 18 Jan 2019. doi:10.2519/jospt.2019.8565.

Background Lumbar spine stability is regularly studied by positioning different loads at different heights and distance and measuring trunk muscle activation changes. Some of these studies have reported sex differences, but this needs to be revisited while controlling for confounding factors. Method 20 males and 20 females sustained three static standing postures, with various loads (0, 5 and 10% of body weight), to evaluate the effect of height and distance. Activation of 12 trunk muscles was recorded with surface electromyography (EMG). Results Females activated their external obliques a little more than males, with increases ranging between 1.5 and 2.3% of maximal voluntary activation (MVA), which corresponds to strong effect sizes (Cohen’s d ranging between 0.86 and 1.13). However, the significant Sex × Height, Sex × Distance and Sex × Load interactions observed for different trunk muscles led to small differential effects (≤1% MVA). Increasing load height slightly increased and decreased back and abdominal muscle activation, respectively, generally by less than 1% MVA. Conclusion The higher activation of the external obliques observed in females might be of clinical value, relative to the required overall trunk muscle activation (5%), to preserve lumbar stability. Other effects were negligible.

Background Previous findings suggest that wearing a lumbar belt may benefit some patients with low back pain; however, the mechanisms of action are not yet fully understood. Research question The effect of wearing two flexible (extensible and non-extensible) lumbar belts on trunk postural control was investigated during an unstable sitting task. Methods Healthy subjects and subjects with LBP sat on a wobbling chair, with and without the lumbar belts. Chair rotation was measured in the sagittal and frontal planes, and 10 linear and nonlinear measures of balance were computed to assess the quantity (3 measures) and quality (7 measures) of the movements. Results Both lumbar belts induced similar changes in specific measures of trunk postural control, for both subject groups, generally indicative of more instability and less controllability, but with low effect sizes (0.14 and 0.40). Subjects with LBP also showed lower entropy (complexity; effect size 0.93) and higher determinism (predictability; effect size 0.56) than healthy controls, under all test conditions. These findings indicate that the subjects with LBP used a less complex, more predictable trunk postural control strategy, suggestive of impaired adaptability and responsiveness to dynamic trunk postural control demands. The findings also suggest other factors related to dynamic adaptability may be impaired by lumbar belt use. Significance The effects of the lumbar belts on trunk postural control were small, however, their practical implications for the management of LBP remain to be determined in relation to other effects of lumbar belts (e.g. increased mechanical stiffness).

The 2015 update of the Canadian Stroke Best Practice Recommendations Hyperacute Stroke Care guideline highlights key elements involved in the initial assessment, stabilization, and treatment of patients with transient ischemic attack (TIA), ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage, and acute venous sinus thrombosis. The most notable change in this 5th edition is the addition of new recommendations for the use of endovascular therapy for patients with acute ischemic stroke and proximal intracranial arterial occlusion. This includes an overview of the infrastructure and resources required for stroke centers that will provide endovascular therapy as well as regional structures needed to ensure that all patients with acute ischemic stroke that are eligible for endovascular therapy will be able to access this newly approved therapy; recommendations for hyperacute brain and enhanced vascular imaging using computed tomography angiography and computed tomography perfusion; patient selection criteria based on the five trials of endovascular therapy published in early 2015, and performance metric targets for important time-points involved in endovascular therapy, including computed tomography-to-groin puncture and computed tomography-to-reperfusion times. Other updates in this guideline include recommendations for improved time efficiencies for all aspects of hyperacute stroke care with a movement toward a new median target door-to-needle time of 30 min, with the 90th percentile being 60 min. A stronger emphasis is placed on increasing public awareness of stroke with the recent launch of the Heart and Stroke Foundation of Canada FAST signs of stroke campaign; reinforcing the public need to seek immediate medical attention by calling 911; further engagement of paramedics in the prehospital phase with prehospital notification to the receiving emergency department, as well as the stroke team, including neuroradiology; updates to the triage and same-day assessment of patients with transient ischemic attack; updates to blood pressure recommendations for the hyperacute phase of care for ischemic stroke, intracerebral hemorrhage, and subarachnoid hemorrhage. The goal of these recommendations and supporting materials is to improve efficiencies and minimize the absolute time lapse between stroke symptom onset and reperfusion therapy, which in turn leads to better outcomes and potentially shorter recovery times.

BACKGROUND The function of specific abdominal muscles can be assessed using both electromyography (EMG) and ultrasound imaging (USI) thickness measures. However, the relationship between these two measurements is not conclusive during sitting isometric trunk efforts. OBJECTIVE This study was conducted to assess the relationship between USI thickness and EMG amplitude measures of the right external oblique (EO) muscle during isometric efforts in the sitting position. METHOD Eighteen subjects performed ramp isometric efforts progressing from 0 to 50% of their maximal voluntary contraction (MVC) in three trunk directions on a dynamometer: (1) forward flexion; (2) right lateral flexion; and (3) left axial rotation. USI and surface EMG amplitude measures of the EO muscle were recorded concomitantly and both normalized against rest values and maximal EMG, respectively. RESULTS EO muscle was significantly more activated (p < 0.001) during forward flexion (42% on average) and axial rotation (35%) than during lateral flexion (24%). Non-significant (r=0.01; P=0.979) to highly significant (r=0.98; P < 0.0001) and negative and positive Pearson correlations were observed between EMG and EO thickness measures for both flexion and rotation directions. CONCLUSION The negative correlations between EMG and USI measures as well as the great variability of these correlations across individuals suggest that USI is not a valid measures of EO muscle activity. USI thickness measures should be interpreted with great caution in research and clinical settings.

Spine stability demand influences active-passive coordination of the trunk response, especially during sudden perturbations. The objective of this study was to look at the role of passive, stationary active and reflexive subsystems on spinal stability. Spine stability was evaluated here during pre- and post-perturbation phases by computing the minimum (i.e., critical) muscle stiffness coefficient required to maintain stability. The effects of pre-perturbation conditions (preloading, initial posture and abdominal antagonistic coactivation) as well as perturbation magnitude were studied. Results revealed that higher preload, initially flexed trunk posture and abdominal pre-activation enhanced pre-perturbation stiffness and stability. In contrast to the preload, however, larger sudden load, initial flexion and abdominal preactivation significantly increased post-perturbation stability margin. As a result, much lower critical muscle stiffness coefficient was required post-perturbation. Compared to the pre-perturbation phase, the trunk stiffness and stability substantially increased post-perturbation demanding thus a much lower critical muscle stiffness coefficient. Overall, these findings highlight the crucial role of the ligamentous spine and muscles (in both passive and active states) in augmenting the trunk stiffness and hence stability during pre- and post-perturbation phases; a role much evident in the presence of initial trunk flexion.

Lumbar stabilization programs reduce pain and disability, but the mechanisms of action underlying this treatment are unknown. Trunk postural control during unstable sitting represents a surrogate measure of motor control mechanisms involved to maintain the dynamic stability of the spine. This exploratory study aimed to determine the reliability of trunk postural control measures over an 8-week interval, their sensitivity to low back pain status and treatment and their relationship with clinical outcomes. Trunk postural control measures were determined in patients with low back pain before and after an 8-week lumbar stabilization exercise program. Healthy controls were assessed over the same interval, but without any treatment, to determine the reliability of the measures and act as a control group at baseline. The kinematics of a wobble chair during unstable sitting was summarized using different linear and nonlinear measures quantifying the quantity and quality of movement, respectively. The reliability of the measures was moderate to excellent. The results showed significant reduction in pain and disability following the intervention. While no impairment at baseline scores was found, some linear and nonlinear measures changed over the intervention period among the patient group. However, for nonlinear measures only, significant correlations were detected with the change scores of pain and disability. The change of measures over the intervention period was likely due to learning rather than the intervention as similar alteration was detected in the healthy subjects. The results suggest that only the quality (not the quantity) of movement may have relationship with pain and disability.

Workers with low back pain (LBP) may benefit from wearing a lumbar belt (LB), but the biomechanical and psychological mechanisms involved are not fully understood. Two types of flexible LB (extensible and non-extensible) were compared to a control condition (no LB) regarding pain-related (pain, fear of pain and catastrophizing) and biomechanical (range of motion - ROM) outcomes related to two tasks: maximal trunk flexion-extension and manual material handling. Healthy controls and participants with LBP were tested. During both tasks, the two LBs reduced the lumbar ROM in participants with LBP in the same way as healthy controls. This was observed even at the beginning of the trunk flexion movement, allowing generalization to many work tasks, that is to say tasks performed with small or deep trunk flexion. The two LBs reduced pain, fear of pain and catastrophizing in subjects with LBP. That may help a gradual re-exposure to physical work activities (disability prevention perspective), or maintaining these activities (secondary prevention perspective), following a LBP episode.

The aim of this study was to test whether determinants associated with lumbar stability can predict performance during unstable sitting (trunk postural control - TPC). If confirmed, unstable sitting could be viewed as a proxy measure for these determinants. Wobbling chair motion was measured in 58 subjects with an inertial sensor, and six outcomes were computed (mean frequency and velocity, frequency dispersion, two variables from the sway density analysis and Lyapunov exponent - short interval) to represent TPC performance. Subjects also performed five other trunk neuromuscular tests to quantify the thickness of back and abdominal muscles and connective tissues, lumbar proprioception, lumbar stiffness, feedforward and feedback control mechanisms, and trunk/muscle coordination. Four to five predictors explained between 36 and 47% of TPC outcomes variance, as determined with multivariate analyses. These predictors were mainly related to (1) angular kinematic parameters of the pelvis or lumbar spine following rapid arm movement, (2) lumbar intrinsic stiffness, (3) thickness of perimuscular connective tissues surrounding specific abdominal muscles, (4) activation onsets of specific trunk muscles (IO/TrA and iliocostalis lumborum) before rapid arm movement, and (5) percent thickness change of internal oblique (IO) and transversus abdominis (TrA) muscles. Lumbar proprioception and reflex responses were not predictive, possibly due to the lack of appropriate measurements. These findings support the use of TPC in unstable sitting as a proxy measure for determinants associated with lumbar stability. This might be useful in research and clinical settings, considering time and equipment constraints associated with measuring these determinants individually.

Thirty manual material handlers (15 experts and 15 novices) were invited to perform series of box transfers under conditions similar to those of large distribution centers. The objective of the present study was to verify whether multiple box transfers leading to fatigue would also lead to differences between expert and novice workers in joint motions and in back loading variables (L5/S1 moments). The task consisted in transferring 24 15-kg boxes from one pallet to another (4 layers of boxes; 6 boxes/layer: 3 in the front row, 3 in the back) at a self-determined pace and then at an imposed pace of 9 lifts/min for a total of 240 lifts. The underlying idea was to set a challenging task that would force the experts to use their skills. Full-body 3D kinematic data were collected as well as external foot forces. A dynamic 3D linked segment model was used to estimate the net moments at L5/S1. The results clearly show that the experts bent their lumbar spine less (10° less) and were closer (4 cm) to the box than novice workers. Knee flexions were similar in both groups except when the box was lifted from ground level (expert ≈ 71°, novice ≈ 48°). The peak resultant moment was not statistically different (expert = 168 Nm, novice = 184 Nm) although experts had lower values on average than novices when lifting heights (and deposit heights) of the boxes increased. Therefore, experts differed from novice workers mostly in the posture-related variables. These differences are especially important to consider when the box is located on the ground, as the back posture and back loading are then at their greatest magnitude and could have a major impact on the distribution of internal forces on the spine.

This study sought to determine whether repetition-induced summation of activity-related pain (RISP) could be demonstrated in healthy individuals in response to experimentally induced musculoskeletal pain. This study also assessed the effects of transcutaneous electrical nerve stimulation on RISP. The relation between the index of RISP and psychological factors such as catastrophizing and fear of pain was also explored. The sample consisted of 56 healthy (35 women, 21 men) participants who underwent 2 testing sessions, separated by 24 hours. In the first session, musculoskeletal pain was induced with a delayed-onset muscle soreness protocol. During the second session, participants were randomly assigned to the transcutaneous electrical nerve stimulation or placebo condition and were asked to rate their pain as they lifted a series of 18 weighted canisters. An index of RISP was derived as the change in pain ratings across repeated lifts. Approximately 25% of participants showed evidence of RISP. Results also revealed that transcutaneous electrical nerve stimulation attenuated the RISP effect. Psychological measures (fear of pain, catastrophizing) were not significantly correlated with the index of RISP, but the index of RISP was significantly correlated with a measure of physical tolerance. Discussion addresses the clinical implications of the findings as well as the potential mechanisms underlying RISP. Perspective This study showed that RISP could be demonstrated in healthy individuals in response to experimentally induced musculoskeletal pain with delayed-onset muscle soreness. Transcutaneous electrical nerve stimulation led to a significant reduction in RISP.

This study examined the relation between return to work and the maintenance of treatment gains made over the course of a rehabilitation intervention. The study sample consisted of 110 individuals who had sustained whiplash injuries in rear collision motor vehicle accidents and were work-disabled at the time of enrolment in the study. Participants completed pre- and post-treatment measures of pain severity, disability, cervical range of motion, depression, posttraumatic stress symptoms, and catastrophizing. Pain severity was assessed again at 1-year follow-up. At 1-year follow-up, 73 participants had returned to work and 37 remained work-disabled. Analyses revealed that participants who returned to work were more likely to maintain treatment gains (77.5%) than participants who remained work-disabled (48%), χ = 6.3, P < 0.01. The results of a regression analysis revealed that the relation between return to work and the maintenance of treatment gains remained significant (β = 0.30, P < 0.01), even when controlling for potential confounders such as pain severity, restricted range of motion, depression, and pain catastrophizing. The Discussion addresses the processes by which prolonged work-disability might contribute to the failure to maintain treatment gains. Important knowledge gaps still remain concerning the individual, workplace, and system variables that might play a role in whether or not the gains made in the rehabilitation of whiplash injury are maintained. Clinical implications of the findings are also addressed.

OBJECTIVES: This study examined the effect of pain interference and attentional interference on the anticipatory postural adjustments of trunk muscles in patients with nonspecific chronic low back pain. METHODS: Fifty-nine patients performed rapid flexion movements of the right arm under 6 conditions, namely a control condition and conditions with different attention demands. The latency between the activations of the shoulder and different trunk muscles, as measured with surface electromyography, was used as the outcome. Using repeated measures analysis of variance, attention conditions and group comparisons were tested between those who scored high and low on pain intensity, fear of movement, or pain catastrophizing. RESULTS: There were significant (although minimal) interactive effects but significant and potentially clinically relevant group and attention main effects. The group with the lowest scores showed delayed activity (14 to 29 ms) relative to those with higher scores. One attention-demanding condition delayed (20 to 35 ms) the latencies of some trunk muscles relative to the control condition, namely the one that was the most attention-demanding according to the reaction time results. DISCUSSION: These findings suggest that patients with chronic low back pain, who are characterized by higher scores on some pain-related variables (visual analog scale, Tampa Scale of Kinesiophobia, Pain Catastrophizing Scale), react favorably to protect the spine from further pain and injuries but would be at greater risk of injury when performing a complex physical task requiring more attention demand.

Background Lumbar stabilization exercise programs (LSEP) produce positive effects on clinical outcomes, but the underlying mechanisms remain relatively unexplored. Psychological and neuromuscular mechanisms can be involved, such as a better activation of the lumbar multifidus, which represents one possibility. Objectives To determine the following: (1) the effect of an LSEP on lumbar multifidus muscle thickness and activation, as measured with rehabilitative ultrasound imaging (RUSI), in patients with low back pain (LBP); (2) the correlation between RUSI measures and any change in clinical outcomes following the LSEP; and (3) the reliability of RUSI measures in control subjects over 8 weeks. Design One-arm clinical trial with healthy subjects as a control group; reliability study. Setting LSEP delivered in a clinical setting; outcomes measured in a laboratory setting. Participants A total of 34 patients with nonacute LBP and 28 healthy control subjects. Methods Outcomes were measured before and after an 8-week LSEP in patients with LBP, and at the same time interval (without treatment, to assess reliability) in control subjects. Main Outcome Measurements Pain numeric rating scale, Oswestry Disability Index (function), as well as RUSI measures for the lumbar multifidus (LM) muscles at 3 vertebral levels (L5-S1, L4-5, and L3-4) during rest (static) and dynamic contractions (percent thickness change). Results Patients did not show systematic changes in RUSI measures relative to controls, even though RUSI impairments were observed at baseline (dynamic measure at L5-S1) and even though patients had significant improvements in pain and disability. Correlational analyses with these clinical outcomes suggested that patients had reduced muscle thickness at baseline that was associated with a greater reduction in disability following LSEP; however, LM activation measured at baseline showed the opposite. Static RUSI measures showed excellent reliability at the L4-5 and L3-4 levels, whereas dynamic measures were not reliable. Conclusions Patients showed less muscle activation than controls at baseline (L5-S1 level), but the LSEP did not normalize this impairment. The links between RUSI measures and the change in clinical outcomes during LSEP should be further explored. This clinical trial has been recorded in the International Standard Registered Clinical/soCial sTudy Number (ISRCTN) registry (ID: ISRCTN94152969). Level of Evidence II

Background Lumbar stabilization exercise programs should normalize the aberrant movements patterns often observed in patients with low back pain. This study aimed to determine the effect of an 8-week lumbar stabilization program on EMG/kinematics measures of the aberrant movement patterns in such patients. A secondary goal was to assess the 8-week test-retest reliability of these measures. Methods The patients followed an 8-week lumbar stabilization program while no intervention was carried out on the controls. Before and after this period, kinematics of the spine along with the EMG of paraspinal muscles were recorded during trunk maximal flexion-extension. ANOVAs tested the effect of the intervention in the patients, relative to the controls. Within the patients, correlation of the EMG/kinematics measures with the change in disability and pain following the intervention was investigated. Findings A significant reduction in pain (Hedges's g effect size = 2.31) and improvement in function (g = 1.74) was reported in the patients. While EMG/kinematics measures disclosed impairments in the patients at baseline compared to the controls, no change was observed over the intervention. Nevertheless, the change of lumbar range of motion was positively correlated (r = 0.42; P = 0.015) with the change in disability. Interpretation Although pain and disability decreased following the intervention, the EMG/kinematics measures did not change concomitantly suggesting that the patients learned to stiffen the lumbar spine during the treatment, and this technique was applied even if pain and disability unequivocally decreased after the treatment, which would not necessarily be beneficial to the patient.

Objectives Previous research has shown that sensitivity to movement-evoked pain is associated with higher scores on self-report measures of disability in individuals who have sustained whiplash injuries. However, it remains unclear whether sensitivity to movement-evoked pain is associated with work-disability. The aim of the present study was to examine the relation between sensitivity to movement-evoked pain and occupational status in individuals receiving treatment for whiplash injury. Methods A sample of 105 individuals with whiplash injuries participated in a testing session where different measures of pain (i.e. spontaneous pain, multi-site pain, sensitivity to movement-evoked pain) were collected during the performance of a simulated occupational lifting task. Results Hierarchical logistic regression analysis revealed that the measures of multisite pain and sensitivity to movement-evoked pain made significant independent contributions to the prediction of work-disability. Discussion The findings suggest that including measures of multisite pain and sensitivity to movement evoked pain in assessment protocols has the potential to increase the value of pain assessments for the prediction of occupational disability associated with whiplash injury. Clinical and theoretical implications of the findings are addressed.

Background Quantifying the integrity of the Achilles tendon (AT) is a rehabilitation challenge. Adopting quantitative ultrasound measurements (QUS measurements) of the AT could fill this gap by 1) evaluating the test-retest reliability and accuracy of QUS measurements of the AT; 2) determining the best protocol for collecting QUS measurements in clinical practice. Methods A total of 23 ATs with symptoms of Achilles tendinopathy and 63 asymptomatic ATs were evaluated. Eight images were recorded for each AT (2 visits × 2 evaluators × 2 images). Multiple sets of QUS measurements were taken: geometric (thickness, width, area), first-order statistics (computed from a grayscale histogram distribution: echogenicity, variance, skewness, kurtosis, entropy) and texture features (computed from co-occurrence matrices: contrast, energy, homogeneity). A generalizability study quantified the reliability and standard error of measurement (accuracy) of each QUS measurement, and a decision study identified the best measurement taking protocols. Results Geometric QUS measurements demonstrated excellent accuracy and reliability. QUS measurements computed from the grayscale histogram distribution revealed poor accuracy and reliability. QUS measurements derived from co-occurrence matrices showed variable accuracy and moderate to excellent reliability. In clinical practice, using an average of the results of three images collected by a single evaluator during a single visit is recommended. Conclusions The use of geometric QUS measurements enables quantification of AT integrity in clinical practice and research settings. More studies on QUS measurements derived from co-occurrence matrices are warranted.

Muscle force partitioning methods and musculoskeletal system simplifications are key modeling issues that can alter outcomes, and thus change conclusions and recommendations addressed to health and safety professionals. A critical modeling concern is the use of single-joint equilibrium to estimate muscle forces and joint loads in a multi-joint system, an unjustified simplification made by most lumbar spine biomechanical models. In the context of common occupational tasks, an EMG-assisted optimization method (EMGAO) is modified in this study to simultaneously account for the equilibrium at all lumbar joints (M-EMGAO). The results of this improved approach were compared to those of its conventional single-joint equivalent (S-EMGAO) counterpart, the latter method being applied to the same lumbar joints but one at a time. Despite identical geometrical configurations and passive contributions used in both models, computed outcomes clearly differed between single- and multi-joint methods, especially at larger trunk flexed postures and during asymmetric lifting. Moreover, muscle forces predicted by L5-S1 single-joint analyses do not maintain mechanical equilibrium at other spine joints crossed by the same muscles. Assuming that the central nervous system does not attempt to balance the external moments one joint at a time and that a given muscle cannot exert different forces at different joints, the proposed multi-joint method represents a substantial improvement over its single-joint counterpart. This improved approach, hence, resolves trunk muscle forces with biological integrity but without compromising mechanical equilibrium at the lumbar joints.

Purpose: Roman chair exercises are popular for improving back muscle endurance but do not specifically target back muscles. This study aimed to determine whether an adaptation of the Roman chair exercise would induce more fatigue in back muscles than in hip extensors. Methods: For this study, 16 healthy subjects and 18 patients with nonspecific chronic low back pain performed trunk flexion-extension cycles until exhaustion in a Roman chair with hips flexed at 40°. Surface EMG signals were recorded bilaterally on four back muscles and two hip extensors (gluteus maximus and biceps femoris). Motion analysis of the trunk segments (pelvis, lumbar, and thoracic spines) was also carried out. Results: In both groups, EMG revealed clear evidence of muscle fatigue for the gluteus maximus, less clear evidence of fatigue for the lower back muscles, and motor unit recruitment (without fatigue) for the upper back muscles and biceps femoris. A change of muscle activation pattern was emphasized throughout the exercise bout, with some lower back muscles showing an increase followed by a decrease or leveling off of activation and with upper back muscles showing an increased activation at the end. Kinematic analyses revealed a progressive decrease (11°) in the lumbar range of motion (ROM) and a progressive increase in hip (2°) and thoracic (7°) ROM during the exercise bout. Conclusions: Roman chairs allow more freedom to change the kinematics of the spine during the exercise (less lumbar and more thoracic motion) to delay lower back muscle fatigue by sharing the load between the lower and upper back muscles. Even with adaptations to reduce hip extensors fatigue, this may make this exercise not as specific as wanted for fatiguing lower back muscles.

Response surface methodology is used to establish robust and user-friendly predictive equations that relate responses of a complex detailed trunk finite element biomechanical model to its input variables during sagittal symmetric static lifting activities. Four input variables (thorax flexion angle, lumbar/pelvis ratio, load magnitude, and load position) and four model responses (L4-L5 and L5-S1 disc compression and anterior-posterior shear forces) are considered. Full factorial design of experiments accounting for all combinations of input levels is employed. Quadratic predictive equations for the spinal loads at the L4-S1 disc mid-heights are obtained by regression analysis with adequate goodness-of-fit (R(2)98%, p0.05, and low root-mean-squared-error values compared with the range of predicted spine loads). Results indicate that intradiscal pressure values at the L4-L5 disc estimated based on the predictive equations are in close agreement with available in vivo data measured under similar loadings and postures. Combinations of input (posture and loading) variable levels that yield spine loads beyond the tolerance compression limit of 3400 N are identified using contour plots. Ergonomists and bioengineers, faced with the dilemma of using either complex but more accurate models on one hand or less accurate but simple models on the other hand, have thereby easy-to-use predictive equations that quantifies spinal loads and risk of injury under different occupational tasks of interest.

Despite recent advances in modeling of the human spine, simplifying assumptions are still required to tackle complexities. Such assumptions need to be scrutinized to assess their likely impacts on predictions. A comprehensive comparison of muscle forces and spinal loads estimated by a single-joint (L5-S1) optimisation-assisted EMG-driven (EMGAO) and a multi-joint Kinematics-driven (KD) model of the spine under symmetric (symmetric trunk flexion from neutral upright to maximum forward flexion) and asymmetric (holding a load at various heights in the right hand) activities is carried out. Regardless of the task simulated, the KD model predicted greater activities in extensor muscles as compared to the EMGAO model. Such differences in the symmetric tasks was due mainly to the distinct approaches to resolve the redundancy while in the asymmetric tasks they were due also to the different methods used to estimate joint moments. Shear and compression forces were generally higher in the KD model. Differences in predictions between these modeling approaches varied depending on the task simulated and the joint considered in the single-joint EMGAO model. The EMGAO model should incorporate a multi-joint strategy to satisfy equilibrium at different levels while the KD model should benefit from recorded EMG activities of the antagonistic muscles to supplement input measured kinematics.

The assessment of trunk muscle activation and coordination using dynamometric measurements made in one anatomical plane has hardly minimized the production of out-of-plane coupled moments (CMs). This absence of control may add much variability in moment component partition as well as in recorded muscle activation. The aim of the study was to assess whether providing these CMs as visual feedback efficiently reduces them and whether this feedback influences trunk muscle activation. Twenty men performed five 5-s static ramp submaximal contractions, ranging from 0% to 55% of the maximal voluntary contraction (MVC), in six different directions while standing in a static dynamometer measuring L5/S1 moments. For each direction, four feedback conditions were offered, ranging from simple 1D-feedback in the primary plane of exertion, to full 3D-feedback. Surface electromyographic signals were collected for eight back and six abdominal muscles. Muscle activation amplitudes and CMs were extracted at each 10% force level from 10% to 50% maximum voluntary contraction (MVC). Providing 3D-feedback significantly reduced the CMs, at 50% MVC, by about 1-6%, 1-8% and 2-10% MVC in the sagittal, frontal and transverse planes, respectively. Providing 3D-feedback produced relatively small systematic effects (2-7%) on trunk muscle activation. However, the subjects responded differently to adequately control the coupled moments, leading in some cases to relatively high inter-individual differences in muscle activation. Interestingly, the statistical differences, and size of the effects, were mainly observed when the primary exertions were performed in the frontal and transverse planes. The implications of these findings are discussed.

This study aimed at documenting the reliability of different thresholds used for defining the muscular rest of the trapezius muscles of 27 computer office workers, using surface electromyography (EMG) signals collected in the field. Measurement strategies for increasing the reliability of the results were also explored. Ten different thresholds to define muscular rest were compared: 1) five normalised (individualised) thresholds; 2) three absolute thresholds (in muV); 3) two absolute but individualised thresholds. The reliability was assessed using both a 15-min standardised computer task and 45 min of regular computer work. The main findings were: 1) overall, in a repeated measures study design, muscular rest variables were more reliable with the use of absolute thresholds when compared to normalised and individualised thresholds; 2) excellent reliability (index of dependability0.75) can be reached when averaging the scores over 2 days; 3) using a standardised task instead of regular work does not necessarily lead to more reliable results.

Accurate quantification of the trunk transient response to sudden loading is crucial in prevention, evaluation, rehabilitation and training programs. An iterative dynamic kinematics-driven approach was used to evaluate the temporal variation of trunk muscle forces, internal loads and stability under sudden application of an anterior horizontal load. The input kinematics is hypothesized to embed basic dynamic characteristics of the system that can be decoded by our kinematics-driven approach. The model employs temporal variation of applied load, trunk forward displacement and surface EMG of select muscles measured on two healthy and one chronic low-back pain subjects to a sudden load. A finite element model accounting for measured kinematics, nonlinear passive properties of spine, detailed trunk musculature with wrapping of global extensor muscles, gravity load and trunk biodynamic characteristics is used to estimate the response under measured sudden load. Results demonstrate a delay of approximately 200ms in extensor muscle activation in response to sudden loading. Net moment and spinal loads substantially increase as muscles are recruited to control the trunk under sudden load. As a result and due also to the trunk flexion, system stability significantly improves. The reliability of the kinematics-driven approach in estimating the trunk response while decoding measured kinematics is demonstrated. Estimated large spinal loads highlight the risk of injury that likely further increases under larger perturbations, muscle fatigue and longer delays in activation.

To examine the effect of pelvic stabilization and two lower-limb configurations on the EMG activity of back and hip extensor muscles during a dynamic back extension exercise on a machine and to compare them between sexes.Twenty-two healthy volunteers (11 men and 11 women) performed five trunk flexion-extension cycles at 40% of their maximal voluntary contraction (MVC) in a machine designed for back exercise. Two different positions were used: 1) seated position (seat horizontal, knees at 90 degrees ) and 2) semisitting position (seat slightly tilted forward at 15 degrees , knees at 45 degrees of flexion). In each position, three pelvic stabilization conditions were tested: 1) unrestrained (control condition), 2) partially restrained (posteriorly), and 3) totally restrained (posteriorly and anteriorly). EMG signals were recorded bilaterally with 12 pairs of electrodes placed on back muscles as well as on the gluteus maximus and biceps femoris. The muscular activation level, that is, the percentage of EMG amplitude relative to the maximal EMG obtained from MVC, was used to asses the relative contribution of each muscle group across exercises.In both sexes, two main results were found: 1) pelvic stabilization (partially and totally restrained) significantly (P0.05) increased the activity of all back muscles (average of 12%) and 2) semisitting position significantly decreased (range = 8-27%) the activity of two hip extensors compared with the seated position. Sex differences were also observed relative to the activity of some back muscles as well as the biceps femoris.Combining pelvic stabilization and semisitting position in back exercise machines might be a useful way to localize the effects of endurance training at the back muscles and this in both the sexes.

Objective: To assess the effect of pelvic stabilization and hip position on the electromyographic activity of trunk extensors during Roman chair exercise. A secondary objective was to compare genders. Design: Repeated measures. Subjects: Eleven men and 11 women volunteers. Methods: Five trunk flexion-extension cycles for 3 Roman chair conditions: (i) pelvis unrestrained; (ii) pelvis restrained; and (iii) hip at 40° flexion. Electromyographic signals were recorded on the back muscles, as well as on the gluteus maximus and biceps femoris. The percentage of electro¬myographic amplitude relative to the maximal activity was used to assess the level of muscular activation of each muscle group across the exercises. Results: For both genders, the Roman chair conditions did not influence the activity of the back and gluteus muscles. The hip-at-40°-flexion condition significantly reduced the activity of the biceps femoris (average of 4–18%) relative to the other 2 conditions. Gender differences were observed on the activity of the biceps femoris in all Roman chair conditions. Conclusion: The hip-at-40°-flexion condition would allow the Roman chair exercise to train the targeted back muscles more specifically by overloading them over a longer duration in order to induce physiological changes.

This study aimed to (1) estimate the reliability of 36 centre of pressure (COP) summary measures in healthy participants and (2) identify the main sources of variability in order to estimate the most appropriate measurement strategies to improve reliability. Twelve healthy males performed, on two separate days, eight 1-min trials of quiet standing on a force platform in two conditions [eyes open (EO) and eyes closed (EC)]. The generalizability theory was used as a framework to estimate the magnitude of the different variance components (Subject, Trial, Day and all interactions) and the reliability of the measures corresponding to various simulations of measurement strategies. Reliability of the COP summary measures was poor to moderate. Intra-class correlation coefficients were generally higher with EO (mean: 0.46, range: 0.03-0.76) than with EC (mean: 0.41, range 0.02-0.72) across all summary measures. The majority of the variance was attributed to Subject (2%-76%), Subject x Day (0%-24%) and Subject x Day x Trial (16%-79%) variance components depending on the summary measure and condition. The reliability could be improved more efficiently by averaging measurements between-days than by increasing the number of trials during 1 day. For the majority of the summary measures, acceptable reliability can be achieved when at least seven or more trials are averaged during the same testing day.

Unstable sitting on a wobble chair with different balance difficulty levels can be used as an effective tool in exercises as well as evaluation and therapeutic stages of rehabilitation. No data on muscle activity levels and spinal loads are however available to assess its safety compared to other regular daily activities. The goal of this study was to estimate muscle forces and spinal loads in a seated unstable wobble chair task. In vivo 3D kinematics of the trunk and seat collected in an earlier study were used here to drive computational trunk musculoskeletal models of 6 normal and 6 low-back pain subject groups sitting on a wobble chair for a duration of 10s. Results revealed no significant differences between kinematics, muscle forces, spinal loads and force plate reaction forces when comparing these two groups. The estimated muscle forces and spinal loads were moderate though larger than those in a stationary sitting posture. Local spinal forces at the L5-S1 disc varied with time and reached their peaks (1473 N and 1720 N in compression, 691 N and 687 N in posterior-anterior shear and 153 N and 208 N in right-left shear, respectively for healthy and CLBP groups) being much greater relative to those in the stationary sitting posture (means of 12 subjects: 768 N, 284 N and 0 N, respectively). The wobble chair with characteristics considered in this study is found hence safe enough as a therapeutic exercise for both healthy and low-back pain subjects.

Ambulatory assessment of trunk posture is important in improving our understanding of the risk of low back injury. Recently, small inertial sensors combining accelerometers, gyroscopes and magnetometers were developed and appear to be promising for measuring human movement. However, the validity of such sensors for assessing three-dimensional (3D) trunk posture in motion has not been documented. The purpose of this study was to evaluate a hybrid system (HS) composed of two inertial sensors for the 3D measurement of trunk posture. A secondary purpose was to explore the utility of adding another source of information, a potentiometer, to measure the relative rotation between both sensors in order to improve the validity of the system. The first sensor was placed over the sacrum and the second on the upper part of the thorax. Both sensors were linked by a flexible rod with a potentiometer. A complementary quaternion filter algorithm was used to estimate trunk orientation by taking advantage of the nine components of each sensor and the potentiometer. The HS's orientations were compared to those obtained from a 3D optoelectronic system. Validation of the HS was performed in three steps in which six subjects had to perform manual handling tasks in: (1) static postures; (2) dynamic motions of short duration (30s); and (3) dynamic motions of long duration (30min). The results showed that the root mean square (RMS) error of the HS was generally below 3 degrees for the flexion and lateral bending axes, and less than 6 degrees for the torsion axis, and that this error was lower for the short-duration tests compared to the long-duration one. The potentiometer proved to be an essential addition, particularly when the magnetometer signals were corrupted and only the gyroscope and accelerometer could be combined. It is concluded that the HS can be a useful tool for quantifying 3D trunk posture in motion.

Expertise is a key factor modulating the risk of low back disorders (LBD). Through years of practice in the workplace, the typical expert acquires high level specific skills and maintains a clean record of work-related injuries. Ergonomic observations of manual materials handling (MMH) tasks show that expert techniques differ from those of novices, leading to the idea that expert techniques are safer. Biomechanical studies of MMH tasks performed by experts/novices report mixed results for kinematic/kinetic variables, evoking potential internal effect of expertise. In the context of series of box transfers simulated by actual workers, detailed internal loads predicted by a multiple-joint EMG-assisted optimization lumbar spine model are compared between experts and novices. The results confirmed that the distribution of internal moments are modulated by worker expertise. Experts flexed less their lumbar spine and exerted more active muscle forces while novices relied more on passive resistance of the muscles and ligamentous spine. More specifically for novices, the passive contributions came from global extensor muscles, selected local extensor muscles, and passive structures of the lumbar spine (ligaments and discs). The distinctive distribution of internal forces was not concomitant with a similar effect on joint forces, these forces being dependent on external loading which was equivalent between experts and novices. From a safety standpoint, the present results suggest that experts were more efficient than novices in partitioning internal moment contributions to balance net (external) loading. Thus, safer handling practices might be seen as a result of experts׳ experience.

A few biomechanical studies have contrasted the work techniques of female and male workers during manual material handling (MMH). A recent study showed that female workers differed from males mostly in the strategy they used to lift 15-kg boxes from the ground, especially regarding task duration, knee and back postures and interjoint coordination. However, the lifting technique difference observed in females compared to males was perhaps due to a strength differences. The objective of this study was to test whether female workers would repeat the same lifting technique with a load adjusted to their overall strength (females: 10 kg; males: 15 kg), which can be considered a “relative load” since the overall back strength of females is 2/3 that of males. The task for the participants consisted in transferring boxes from one pallet to another. A dynamic 3D linked segment model was used to estimate the net moments at L5/S1, and different kinematic variables were considered. The results showed that the biomechanics of the lifting techniques used by males and females were similar in terms of task duration and cumulative loading, but different in terms of interjoint coordination pattern. The sequential interjoint coordination pattern previously seen in females with an absolute load (15 kg) was still present with the relative load, suggesting the influence of factors more intrinsically linked to sex. Considering that the female coordination pattern likely stretched posterior passive tissues when lifting boxes from the ground, potentially leading to higher risk of injury, the reason for this sex effect must be identified so that preventive interventions can be proposed.

Background Adequate neuromuscular control of the lumbar spine is required to prevent lumbar injuries. A trunk postural control test protocol, controlling for the influence of body size on performance, was implemented to carry out between-subject comparisons. The aim of this study was to assess the effect of sex and low back pain status with the use of two measures of trunk postural control, the first based on chair motion, and the second based on trunk motion. Methods Thirty-six subjects (with and without low back pain) performed three 60-s trunk postural control trials with their eyes closed while seated on an instrumented wobble chair, following a calibration procedure. Chair and trunk angular kinematics were measured with an optoelectronic system. A chair-based stabilogram and a trunk-based (lumbar spine) stabilogram were created using the angular motions produced in the sagittal and frontal planes. Twenty body-sway measures were computed for each stabilogram. Findings The calibration task efficiently controlled for the influence of body size. Several sex effects were detected, with most of them originating from the trunk-based measures. Subjects with low back pain and healthy controls showed comparable trunk postural control. Interpretation Sex differences were substantiated for the first time, but almost only with the trunk-based stabilogram, showing that the kinematic information captured on the trunk segments is quite different from what is captured on the wobble chair. Contrary to previous studies, pain status was not related to lowered trunk postural control, which can be attributed to the patients recruited or measurement reliability issues.