Temporal Associations Between Pain-Related Factors and Abnormal Muscle Activities in a Patient with Chronic Low Back Pain: A Cross-Lag Correlation Analysis of a Single Case

PURPOSE: The cross-sectional and longitudinal associations between pain-related factors and muscle activity in patients with chronic low back pain (CLBP) are unclear. This study aimed to examine the temporal associations between them in a CLBP patient using a single-case analysis to account for an individual course. PATIENT AND METHODS: A patient with a history of lower back pain lasting more than 3 months was studied from March 16, 2020 to May 30, 2020. Surface electromyographic signals were recorded from over the bilateral lumbar erector spinae in the patient while performing a standing trunk flexion and re-extension task. The average value for muscle activity during each movement phase was estimated, and the flexion relaxation ratio (FRR) of all channels was subsequently calculated. Pain-related factors and disability were assessed using questionnaires. All assessments were performed nine times, along with 2–3 months of intervention. Once or twice per week, the patient received physical therapy that consisted of soft tissue mobilization, joint mobilization, nerve mobilization, and patient education. A cross-lag correlation analysis of this single case was conducted. RESULTS: Pain-related factors showed a trend toward improvements in all variables when compared to those in the first assessment; however, there was no general change (increase) in FRR over time. The cross-lag correlation analysis revealed that improvements in FRR were associated with improvements in body perception disturbance (ρ = −0.78, p < 0.01), and that improvements in muscle activity during the extension phase were associated with improvements in pain (ρ = 0.75), psychological factors (ρ = 0.57), and disability (ρ = 0.67) (p < 0.05). CONCLUSION: Our findings suggest that improvements in body perception were temporally associated with improvements in FRR, and improvements in pain, psychological factors, and disability were temporally associated with a reduction in muscle activity during the trunk extension phase in this patient with CLBP.