People with chronic low back pain display spatial alterations in high-density surface EMG-torque oscillations

Abstract

We quantified the relationship between spatial oscillations in surface electromyographic (sEMG) activity and trunk-extension torque in individuals with and without chronic low back pain (CLBP), during two submaximal isometric lumbar extension tasks at 20% and 50% of their maximal voluntary torque. High-density sEMG (HDsEMG) signals were recorded from the lumbar erector spinae (ES) with a 64-electrode grid, and torque signals were recorded with an isokinetic dynamometer. Coherence and cross-correlation analyses were applied between the filtered interference HDsEMG and torque signals for each submaximal contraction. Principal component analysis was used to reduce dimensionality of HDsEMG data and improve the HDsEMG-based torque estimation. sEMG-torque coherence was quantified in the δ(0–5 Hz) frequency bandwidth. Regional differences in sEMG-torque coherence were also evaluated by creating topographical coherence maps. sEMG-torque coherence in the δ band and sEMG-torque cross-correlation increased with the increase in torque in the controls but not in the CLBP group (p = 0.018, p = 0.030 respectively). As torque increased, the CLBP group increased sEMG-torque coherence in more cranial ES regions, while the opposite was observed for the controls (p = 0.043). Individuals with CLBP show reductions in sEMG-torque relationships possibly due to the use of compensatory strategies and regional adjustments of ES-sEMG oscillatory activity.

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

“…The sample size calculation for this study was based on a large effect size of f = 0.4, an α error probability of 0.001, a β power of 0.85, and a potential 10% loss of data due to signal quality or participant withdrawal. The choice of this effect size was based on our previous two-way mixed repeated-measures ANOVA results, related explicitly to CLBP and asymptomatic control differences in torque coefficient of variation (CoV), SD, and centroid of coherence (along the y axis) in the delta band during isometric lumbar extension contractions (12).…”

“…For additional information about the PCA approach, the reader is referred to previous work (12). Before the cross-correlation and coherence computations, the previously offline re-referenced 59 (from the RA and EO muscles, respectively) and the 124 (from the merged electrodes over ES) bipolar HDsEMG channels were processed for PCA calculation as follows (12,16): 1) high-pass filtering at 10 Hz, 2) selection of a subset of channels by applying PCA to the 59 (each abdominal muscle) and the 124 (ES) differential HDsEMG signals in the time domain, 3) full-wave rectification of the selected channels and averaging them to get one time signal for each muscle, 4) low-pass filtering at 10 Hz (additional to the filtering in step 1), to identify slow frequency fluctuations in motor unit firing rate/recruitment (4), 5) smoothing with a Savitzky-Golay filter (first order), and 6) DC (i.e., zero frequency) component removal. This preprocessing was performed for the thoracolumbar ES, only during the extension movement, and for each abdominal muscle, only during the flexion movement (concentric and eccentric).…”

“…We would like to clarify that this study was observational and primarily exploratory in nature. Nevertheless, multiple a priori hypotheses were made based on the findings of previous studies from our group and others (11)(12)(13). Lastly, considering that the reliability of HDsEMG had been previously demonstrated by van Helden et al (30) in asymptomatic controls, we decided not to have participants perform the same test on consecutive days.…”

“…Musculoskeletal pain can significantly impact movement and the ability to control muscle force, potentially due to changes in afferent input from the painful area (6) or neuroplastic changes in the central nervous system (7). For example, previous studies have shown that people suffering from painful musculoskeletal conditions, such as knee osteoarthritis (8), neck pain (9), subacromial impingement syndrome (10), and chronic low back pain (CLBP) (11)(12)(13), present with reduced control of muscle force compared with asymptomatic individuals. However, the specific neuromuscular processes contributing to decreased muscle force control in individuals with pain have yet to be fully understood.…”

Changes in thoracic erector spinae regional activation during postural adjustments and functional reaching tasks after spinal cord injury

“…Research using indwelling EMG electrodes has shown distinct muscle activation between the caudal and cranial regions of the lumbar ES during trunk rotation in healthy adults, suggesting selective control of regions of the ES (29). Studies in clinical populations (e.g., low back pain) have also reported differences in regional activation of the lumbar ES muscles from the healthy controls (17,19,30,31). Here, for the rst time, we examined the spatial distribution of the thoracic ES activity in individuals with chronic, incomplete SCI during postural tasks where the role of the ES is to maintain an upright posture.…”