Multimodal assessment of central and peripheral neuromuscular function during core stability tasks in chronic nonspecific low back pain

Chronic non-specific low back pain (cNSLBP) involves central sensorimotor deficits, but the task-dependent interplay between brain activity and muscle coordination remains poorly understood. This study employed a novel multimodal approach to concurrently assess cortical activation and muscle complexity in cNSLBP patients and healthy controls (HC) during two core tasks with distinct demands. 24 cNSLBP patients and 24 HC performed two static tasks, a symmetric plank (PL) and an asymmetric modified bird-dog (MBD) task. Cortical activation was measured via functional near-infrared spectroscopy (fNIRS; ΔHbO). Muscle activation complexity was quantified from surface electromyography (sEMG) using Fuzzy Entropy (FuzEn). For fNIRS, the left precentral and postcentral gyri (L Pr–PoCG) showed a significant group main effect (p = 0.0402*, η2 = 0.0885), with cNSLBP patients having lower ΔHbO than HCs across both tasks, and a significant task main effect (p = 0.0361*, η2 = 0.0903) without Group × Task interaction (p = 0.6854). For sEMG, no between-group FuzEn differences were found in core muscles (all p > 0.05), but significant task main effects were observed in the left rectus abdominis (L RA; p = 0.0394*, η2 = 0.0766) and left external oblique (L EO; p = 0.0394*, η2 = 0.0709). No significant between-group differences in brain–muscle coupling strength were detected. This study confirms task-specific central–peripheral dysregulation in cNSLBP, characterized by persistent L Pr–PoCG hypoactivation (indicating impaired sensorimotor integration) and task-dependent changes in core muscle activation complexity, which are prominent during asymmetric tasks. These findings emphasize the value of static asymmetric tasks for assessing latent neuromuscular deficits and guide targeted interventions for cortical and muscular dysfunction.