Hakim Mecheri

Poor back muscle endurance is related to pain catastrophizing in patients with chronic low back pain.

Study Design. An experimental and comparative study of chronic low back pain (CLBP) patients and healthy controls. Objective. To use a motivation-independent electromyography (EMG) based test of back muscle capacity to determine whether back muscle deconditioning is present in CLBP patients and whether it is related to pain-related psychological variables. Summary of Background Data. The verification of the deconditioning syndrome in CLBP patients might be biased by the use of performance-based measures to assess physical fitness, especially in patients having fear of injury. Also, the use of lumbar-specific measures of physical fitness, such as back muscle strength and endurance, might be more sensitive to physical deconditioning than more general assessments such as aerobic capacity. Methods. A time-limited submaximal fatigue test was performed by 27 nonspecific CLBP subjects (14 men) who had not had any surgery, and 31 healthy controls (17 men) while surface EMG signals were collected from back muscles. Motivation-independent EMG indices, which are sensitive to muscle fatigue or to activation patterns, were then computed and entered as input into previously developed regression equations to predict endurance (PTend) and strength (PStrength). Between-group comparisons were completed with patients divided in subgroups based on a median split of pain intensity, fear of movement, or pain catastrophizing scores. Results. Differences between healthy and CLBP subgroups were mainly observed when patients were divided using pain catastrophizing scores (PCS). High-PCS patients showed significantly lower PTend than low-PCS patients. Various EMG indices showed comparable results to PTend. However, some of them also pointed out that the PCS-low patients were more fatigue-resistant and showed different activation patterns comparatively to healthy subjects. Conclusion. These results suggest that physical deconditioning that is specific to back muscle capacity was present in a subgroup of patients while the opposite was observed in another subgroup, pain catastrophizing being related to this outcome. These findings support previous theoretical models of pain/disability.

The effect of sex and chronic low back pain on back muscle reflex responses.

Different back muscle reflex assessment protocols have shown abnormally longer reflex latency responses of back muscles in chronic low back pain (CLBP). However, many confounding variables are difficult to control, such as the load magnitude and the preactivation of trunk muscles. The aims of this study were to evaluate, in 30 subjects with CLBP and 30 healthy controls, the activation levels of back muscles during pre-loading and their reflex responses to sudden loading. After subjected to six practice perturbations, 20 sudden and unexpected forward perturbations of the trunk were applied in 30 CLBP subjects (14 women) and 31 controls (17 women), while attempting to minimize the confounding effect of preactivation level and perturbation amplitude. Reflex latency and amplitudes were computed from the surface EMG signals of four back muscles (bilaterally at L5, L3, L1, T10 vertebral levels). EMG was also collected from abdominal muscles. Subjects with CLBP significantly increased the preactivation of back muscles (abdominal preactivation the same) relative to controls while no sex effect was observed. While adjusting statistically for these differences, reflex amplitude was significantly higher in subjects with CLBP and men, compared to healthy controls and women, respectively. Interestingly, contrary to most of the literature available, no between-group effects were detected for reflex latency, which could potentially be explained by an appropriate control of confounding variables, but this remains to be clarified in future research.

Criterion validity and between-day reliability of an inertial-sensor-based trunk postural stability test during unstable sitting

INTRODUCTION Adequate neuromuscular control of the lumbar spine is required to prevent lumbar injuries. A trunk postural stability test has been proposed earlier, using a chair wobbling on a central pivot and four springs with adjustable positions to modulate task difficulty. An inertial sensor is fixed on the chair to measure postural sway. The aim of this study is to assess the criterion validity and between-day reliability of the calibration and testing components. METHODS Thirty six subjects (with and without low back pain) followed a calibration procedure, four practice trials and three 60-s trials on 2days. The criterion validity of the inertial sensor was tested against an optoelectronic system and a force platform. The reliability of 38 body sway measures obtained from the inertial sensor angular measures was estimated. RESULTS The inertial sensor led to valid estimates of postural sway. The reliability of the calibration procedure was moderate. Practically no learning effect was detected except for a few body sway measures in patients with CLBP. Three 60-s trials provided acceptable reliability for approximately half of the body sway measures, although this is more difficult to achieve in patients with CLBP. DISCUSSION The use of an easy to use inertial sensor led to valid measures of postural sway. A number of body sway measures were identified as reliable tools for individual follow-ups but inter-subject comparisons were anticipated as more difficult when patients with CLBP are involved.

Trunk response to sudden forward perturbations – Effects of preload and sudden load magnitudes, posture and abdominal antagonistic activation

Unexpected loading of the spine is a risk factor for low back pain. The trunk neuromuscular and kinematics responses are likely influenced by the perturbation itself as well as initial trunk conditions. The effect of four parameters (preload, sudden load, initial trunk flexed posture, initial abdominal antagonistic activity) on trunk kinematics and back muscles reflex response were evaluated. Twelve asymptomatic subjects participated in sudden forward perturbation tests under six distinct conditions. Preload did not change the reflexive response of back muscles and the trunk displacement; while peak trunk velocity and acceleration as well as the relative load peak decreased. Sudden load increased reflex response of muscles, trunk kinematics and loading variables. When the trunk was initially flexed, back muscles latency was delayed, trunk velocity and acceleration increased; however, reflex amplitude and relative trunk displacement remained unchanged. Abdominal antagonistic preactivation increased reflexive response of muscles but kinematics variables were not affected. Preload, initial flexed posture and abdominal muscles preactivation increased back muscles preactivity. Both velocity and acceleration peaks of the trunk movement decreased with preload despite greater total load. In contrast, they increased in the initial flexed posture and to some extent when abdominal muscles were preactivated demonstrating the distinct effects of pre-perturbation variables on trunk kinematics and risk of injury.

Reliability of Ultrasound Measures of the Transversus Abdominis: Effect of Task and Transducer Position

To assess the reliability of ultrasound (US) measures of the transversus abdominis (TrA) muscle in a sample of subjects with and without specific chronic low back pain and to test whether reliability is enhanced by using different abdominal muscle activation tasks, with use of a foam cube for US transducer stabilization or by averaging 3 measures on the same image.

Ultrasound Measures of the Lumbar Multifidus: Effect of Task and Transducer Position on Reliability

To (1) assess the intra‐ and inter‐rater reliability of different ultrasound (US) measures of the lumbar multifidus muscle in subjects with and without chronic low back pain and (2) test 3 different ways to enhance reliability, that is, by testing different tasks, using a template, and averaging trials within or between days.

Accuracy and repeatability of single-pose calibration of inertial measurement units for whole-body motion analysis

Portable inertial measurement units (IMUs) are suitable for motion analysis outside the laboratory. However, IMUs depend on the calibration of each body segment to measure human movement. Different calibration approaches have been developed for simplicity of use or similarity to laboratory motion analysis, but they have not been extensively examined. The main objective of the study was to determine the accuracy and repeatability of two common single-pose calibrations (N-pose and T-pose) under different conditions of placement (self-placement and passive placement), as well as their similarity to laboratory analysis based on anatomical landmarks. A further aim of the study was to develop two additional single-pose calibrations (chair-pose and stool-pose) and determine their accuracy and repeatability. Postures and movements of 12 healthy participants were recorded simultaneously with a full-body IMU suit and an optoelectronic system as the criterion measure. Three repetitions of the T-pose and the N-pose were executed by self-placement and passive placement, and three repetitions of the chair-pose and stool-pose were also performed. Repeatability for each single-pose calibration showed an average intraclass correlation coefficient for all axes and joints between 0.90 and 0.94 and a standard error of measurement between 1.5° and 2.1°. The T-pose with passive placement is recommended to reduce longitudinal axis offset error and to increase similarity to laboratory motion analysis. Finally, the chair-pose obtained the least longitudinal axis offset error amongst the tested poses, which shows potential for IMU calibration.

Identification of intrinsic and reflexive contributions to low-back stiffness: medium-term reliability and construct validity.

This study aimed at testing the reliability and construct validity of a trunk perturbation protocol (TPP) that estimates the intrinsic and reflexive contributions to low-back stiffness. The TPP consists of a series of pseudorandom position-controlled trunk perturbations in an apparatus measuring forces and displacements at the harness surrounding the thorax. Intrinsic and reflexive contributions to low-back stiffness were estimated using a system identification procedure, leading to 12 parameters. Study 1 methods (reliability): 30 subjects performed five 75-s trials, on each of two separate days (eight weeks apart). Reliability was assessed using the generalizability theory, which allowed computing indexes of dependability (ϕ, analogous to intraclass correlation coefficient) and standard errors of measurement (SEM). Study 2 methods (validity): 20 healthy subjects performed three 75-s trials for each of five experimental conditions assumed to provide different lumbar stiffness; testing the construct validity of the TPP using four conditions with different lumbar belt designs and one control condition without. Study 1 results (reliability): Learning was seen between the first and following trials. Consequently, reliability analyses were performed without the first trial. Simulations showed that averaging the scores of three trials can lead to acceptable reliability results for some TPP parameters. Study 2 results (validity): All lumbar belt designs increased low-back intrinsic stiffness, while only some of them decreased reflex stiffness, which support the construct validity of the TPP. Overall, these findings support the use of the TPP to test the effect of rehabilitation or between-groups differences with regards to trunk stiffness.

The effect of different lumbar belt designs on the lumbopelvic rhythm in healthy subjects

BackgroundResearch suggests that in some patients with low back pain, lumbar belts (LB) may derive secondary prophylactic benefits. It remains to be determined, however, which patients are most likely to benefit from prophylactic LB use, and which LB design is optimal for this purpose. The objective of this study was to determine the effect of different lumbar belts designs on range of motion and lumbopelvic rhythm.MethodsHealthy subjects (10 males; 10 females) performed five standing lumbar flexion/extension cycles, with knees straight, during a control (no belt) and four lumbar belt experimental conditions (extensible, with and without dorsal and ventral panels; non-extensible). Motion of the pelvis and lumbar spine was measured with 3D angular inertial sensors.ResultsThe results suggest that adding dorsal and ventral panels to an extensible LB produces the largest lumbar spine restrictions among the four tested lumbar belt designs, which in turn also altered the lumbopelvic rhythm. On a more exploratory basis, some sex differences were seen and the sex × experimental condition interaction just failed to reach significance.ConclusionsLB may provide some biomechanical benefit for patients with low back disorders, based on the protection that may be provided against soft tissue creep-based injury mechanisms. More comprehensive assessment of different LB designs, with additional psychological and neuromuscular measurement outcomes, however, must first be conducted in order to produce sound recommendations for LB use. Future research should also to take sex into account, with sufficient statistical power to clearly refute or confirm the observed trends.

Trunk postural control in unstable sitting: Effect of sex and low back pain status

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.