Abstract
BACKGROUND: Chronic pain has been reported as one of the leading causes of disability in the world, being associated with a potential impact on autonomic balance. OBJECTIVE: The aim was to compare sympathetic and parasympathetic activity through heart rate variability (HRV) between adults with and without chronic low back pain (CLBP). METHODS: An observational study was conducted in which HRV parameters were recorded using time-domain measures-root mean square of successive differences between consecutive RR intervals (rMSSD), minimum and maximum heart rate variability (Min HR and Max HR), and mean heart rate (Mean HR)-and nonlinear measures-Poincaré plot indices SD1 and SD2, Stress Score (SS), and sympathetic/parasympathetic ratio (S:PS). RESULTS: The results showed statistically significant differences between groups (p < 0.05), with higher parasympathetic activity parameters in the group of healthy subjects (rMSSD: p < 0.001; SD1: p = 0.030) and higher sympathetic activity in the CLBP group (SD2, SS, and S:PS ratio: p < 0.001). All parameters showed large effect sizes. CONCLUSIONS: These findings show the association between autonomic balance mechanisms and pain regulation in adults with CLBP.