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Background/objectives: Individuals with chronic low back pain (CLBP) have altered lumbar multifidus stiffness properties compared to healthy controls. Although neuromuscular electrical stimulation (NMES) application to the multifidus might affect stiffness, this has never been investigated. The aims of this study were to examine the effect of a single NMES treatment on multifidus stiffness and pain intensity in CLBP patients.

Methods: 30 participants (13 male, 17 female) were randomized to one of two intervention ('phasic' and 'combined') protocols with the StimaWELL 120MTRS system. Multifidus stiffness at L4 and L5 was measured via shear-wave elastography (SWE) at rest and in standing prior to, and 15 min after, a 20 min NMES treatment. Pain intensity was measured pre- and post-treatment with the numerical pain rating scale (NPRS).

Results: There were significant increases in resting shear modulus at right L4 (p = 0.001) and bilaterally at L5 (p = 0.017; p = 0.020) in the 'combined' intervention group, and a significant between-group difference at right L4 (p < 0.001). There were significant decreases in standing shear modulus at right L4 (p = 0.015) and left L5 (p = 0.036) in the 'combined' intervention group, and a significant between-group difference at left L5 (p = 0.016). Both groups experienced significant decreases in pain intensity (MD combined group = 1.12, 95% CI [0.34, 1.90], p = 0.011) (MD phasic group = 1.42, 95% CI [0.68, 2.16], p = 0.001).

Conclusions: There were multiple significant changes in multifidus stiffness in the combined group, but not in the phasic group. Both groups experienced significant decreases in low back pain intensity.