Low Back Pain–Induced Dynamic Trunk Muscle Control Impairments Are Associated with Altered Spatial EMG–Torque Relationships

Abstract

Purpose We quantified the relationship between high-density surface electromyographic (HDsEMG) oscillations (in both time and frequency domains) and torque steadiness during submaximal concentric/eccentric trunk extension/flexion contractions, in individuals with and without chronic low back pain (CLBP). Methods Comparisons were made between regional differences in HDsEMG amplitude and HDsEMG-torque cross-correlation and coherence of the thoracolumbar erector spinae (ES), rectus abdominis (RA) and external oblique (EO) muscles between the two groups. HDsEMG signals were recorded from the thoracolumbar ES with two 64-electrode grids and from the RA and EO muscles with a single 64-electrode grid placed over each muscle. Torque signals were recorded with an isokinetic dynamometer. Coherence (δ band (0-5 Hz)) and cross-correlation analyses were used to examine the relationship between HDsEMG and torque signals. For this purpose, we employed principal component analysis to reduce data dimensionality and improve HDsEMG-based torque estimation. Results We found that people with CLBP had poorer control during both concentric and eccentric trunk flexion and extension. Specifically, during trunk extension, they exhibited a higher HDsEMG-torque coherence in more cranial regions of the thoracolumbar ES and a higher HDsEMG-cross-correlation compared to asymptomatic controls. During trunk flexion movements, they demonstrated higher HDsEMG amplitude of the abdominal muscles, with the centre of activation being more cranial and a higher contribution of this musculature to the resultant torque (particularly the EO muscle). Conclusions Our findings underscore the importance of evaluating torque steadiness in individuals with CLBP. Future research should consider the value of torque steadiness training and HDsEMG-based biofeedback for modifying trunk muscle recruitment strategies and improving torque steadiness performance in individuals with CLBP.

Eccentric exercise-induced delayed onset trunk muscle soreness alters high-density surface EMG- torque relationships and lumbar kinematics

“…PPTs were performed only on the right side for all participants over ten testing sites (spanning approximately from L5 to T10) as described previously 22 . At each location, two PPT measurements were performed (randomised order), and the average of the two measurements at each site was used for subsequent analysis (mean thoracolumbar ES sensitivity).…”

“…Reference electrodes (WhiteSensor WS, Ambu A/S, Ballerup, Denmark) were also a xed to the participant's sacrum, the anterior superior iliac spine (ASIS), and wrist. For a comprehensive description and visual representation of the HDsEMG electrode placement, we direct readers to our previous work 22 .…”

“…In this study, these components, which were linear combinations of the original 124 channels, were organized in descending order based on the variance they accounted for, with the rst few components representing the majority of the data's variance. PCs that collectively accounted for a cumulative 85% of the total variance were retained 21,22,28 to keep only the most informative components and improve the signal-to-noise ratio. This process, which marked the initial phase of dimensionality reduction, generated a new matrix containing the eigenvectors of these selected PCs.…”

“…Consequently, the original 124-channel dataset was transformed into a new dataset with reduced dimensionality that explained most of the variance in the data. For further details on the PCA methodology, please refer to earlier work 21,22 .…”

“…PCA acts as a dimensionality-reduction tool that can identify and select a subset of principal components (PCs) accountable for the majority of data variation, thereby explaining most of the variance in the exerted torque 19 . This method has been applied previously to quantify both magnitude and regional alterations in HDsEMG-torque relationships in individuals with and without chronic low back pain (CLBP) during isometric 21 and dynamic trunk extension 22 . However, how these relationships are altered in the presence of thoracolumbar ES DOMS remains unclear.…”