Central and peripheral factors moderating pain effects on motor control and disability in chronic lumbosacral...

Motor control is organized within a hierarchical system in which the sensorimotor cortex generates motor commands that are progressively refined through subcortical and spinal networks before being executed by peripheral muscles. Central factors provide the planning and modulation necessary for movement, while peripheral neuromuscular strategies translate these commands into action.Within this interplay, anticipatory postural adjustments (APAs; feedforward control) and compensatory postural adjustments (CPAs; feedback-based corrections) are key peripheral factors that operate in continuous interaction with cortical processes to preserve motor control and postural stability.

To investigate whether cortical excitability-measured by sensory evoked potentials (SEPs; components N80 and N150) and motor evoked potentials (MEPs)-together with deep trunk muscle activity-assessed using electromyography (EMG) of the abdominal and paraspinal muscles during APA and CPA phases-moderates the relationship between pain characteristics (intensity, duration) and functional outcomes (disability, motor control) in individuals with chronic lumbosacral radicular pain.

This cross-sectional study assessed forty-four participants with chronic unilateral lumbosacral radicular pain secondary to L4/L5 or L5/S1 disc herniation. Moderation analyses were performed using PROCESS (model 1), with predictors (X = pain intensity or duration), outcomes (Y = disability or motor control), and moderators (W = cortical or muscular measures), controlling for age. Conditional effects were estimated at the 16th, 50th, and 84th percentiles. "Ipsilateral" referred to the side of perturbation (non-painful), and "contralateral" to the opposite side.

Sensory cortical excitability (N150 amplitude) significantly moderated the association between pain intensity and disability (interaction: β = - 1.87, 95% CI [- 3.69, - 0.06], p = 0.043). The impact of pain intensity on disability was strongest at the 16th percentile of N150 (β = 3.98, 95% CI [2.61, 5.35], p < 0.001) and weakest at the 84th percentile (β = 1.70, 95% CI [0.03, 3.37], p = 0.046). EMG activity of the ipsilateral abdominal muscle during the APA phase also moderated this relationship (interaction: β = - 2.53, 95% CI [- 4.74, - 0.32], p = 0.026), with effects decreasing from β = 3.87 (95% CI [2.68, 5.07], p < 0.001) at the 16th percentile to β = 1.42 (95% CI [- 0.26, 3.09], p = 0.095) at the 84th percentile. For pain duration, paraspinal MEPs showed only a trend toward moderation (interaction: β = - 0.003, 95% CI [- 0.006, 0.0003], p = 0.072). In contrast, sensory cortical excitability indexed by N80 amplitude significantly attenuated the pain duration-disability association (interaction: β = - 0.218, 95% CI [- 0.379, - 0.056], p = 0.010). Ipsilateral abdominal APA activity similarly moderated this association (interaction: β = - 0.289, 95% CI [- 0.503, - 0.074], p = 0.010). For motor control outcomes, contralateral abdominal APA activity showed a marginal moderation effect (interaction: β = 0.30, 95% CI [- 0.03, 0.63], p = 0.076), with effects strengthening at higher activity levels. No significant moderating effects were observed for pain duration.

Functional outcomes in lumbosacral radicular pain are influenced by the interaction of central and peripheral factors. Enhanced sensory and motor cortical excitability, together with feedforward ipsilateral abdominal muscle activity, moderate the relationship between pain and disability, and are associated with better preservation of motor control. Contralateral APA activity may further modulate the effect of pain on motor control, although this influence was marginal.