Control of trunk muscle force in individuals with low back pain: new insights revealed by high-density surface electromyography

Arvanitidis, Michail ORCID: 0000-0002-3339-6668 (2024). Control of trunk muscle force in individuals with low back pain: new insights revealed by high-density surface electromyography. University of Birmingham. Ph.D.

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Abstract

Low back pain (LBP) is a leading cause of disability worldwide, with chronic non-specific LBP (CLBP) accounting for most cases. It is well-recognised that individuals with LBP exhibit different movement patterns compared to those without pain. Extensive research has examined motor adaptations in individuals with CLBP, highlighting alterations in trunk muscle strength, muscle activity, movement patterns, and proprioceptive acuity. Recent studies have also shown that musculoskeletal pain, including CLBP, can impair muscle force control. However, the concept of force or torque steadiness as a motor adaptation in people with CLBP has been relatively understudied and therefore requires further investigation. This thesis presents research that focuses on enhancing our understanding of motor adaptations in people with CLBP, specifically in relation to changes in the control of trunk muscle force/torque steadiness and the potential underlying neuromuscular mechanisms. To achieve this, it examines the relationship between trunk high-density electromyography (HDsEMG) signals and torque using cross-correlation and coherence analyses, and principal component analysis (PCA) to improve these estimations. The first study examined the control of trunk muscle force and EMG-torque relationships during isometric trunk extension contractions, revealing that individuals with CLBP have poorer control compared to pain-free individuals. People with CLBP performed the contractions with altered recruitment strategies, including a higher contribution of more cranial regions of the lumbar erector spinae (ES) to the resultant torque and a failure to increase the contribution of the lumbar ES to the resultant torque with an increase in load. The second study extended these findings to dynamic trunk flexion/extension concentric and eccentric contractions, showing that the control of trunk muscle force is also impaired during these movements alongside altered recruitment patterns. These involved a higher contribution of the thoracolumbar ES to torque, as observed in the first study during trunk extension contractions, and increased abdominal muscle activity, with the centre of activation being more cranial and a higher contribution of this musculature to the resultant torque (particularly the external oblique muscle) during trunk flexion. In contrast, the third study, which investigated the effects of acute low-back soreness induced by delayed onset of muscle soreness (DOMS) on trunk muscle function, recruitment behaviour, movement patterns, and underlying neuromuscular mechanisms, showed that DOMS did not impair trunk force control. However, EMG-torque relationships and kinematics were altered in a contraction-dependent manner. During eccentric contractions, a decrease in the thoracolumbar ES contribution to the resultant torque was observed, and individuals showed increased lumbar flexion during the more demanding contractions. During concentric contractions, a reduction in thoracolumbar range of motion in the sagittal plane was observed, suggesting the maintenance of a more neutral lumbar spine posture, but no alterations in HDsEMG-torque relationships were observed in the presence of DOMS. These findings suggest that pain-free individuals could adapt their motor strategies and maintain muscle performance despite DOMS. The fourth study was a systematic review and meta-analysis that explored the influence of clinical and experimental musculoskeletal pain on the control of muscle force. The findings of this review suggested that the persistent, multidimensional nature of clinical musculoskeletal pain is related to more pronounced impairments in force control compared to the temporary nature of experimental pain, particularly for the trunk. The results of this thesis underscore the importance of evaluating torque steadiness in individuals with CLBP. The findings indicate that people with CLBP exhibit impaired force control and altered trunk muscle recruitment strategies. Future research should explore the value of torque steadiness training and HDsEMG-based biofeedback for enhancing torque steadiness performance in this patient population. These interventions could lead to better-targeted therapies that address the specific neuromuscular deficits associated with CLBP.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):