Thoracic spine mobilization on autonomic nervous system in a healthy population - a randomized controlled double-blinded feasibility study

Abstract Background Thoracic spine mobilization (TSM) has been proposed to influence autonomic nervous system (ANS) activity, yet evidence remains inconsistent and feasibility of standardised protocols is unclear. This study aimed to evaluate whether a randomized TSM protocol can be implemented successfully in healthy participants and to provide preliminary estimates of its effects on heart rate variability (HRV) and heart rate (HR). Methods A randomized feasibility trial was conducted with healthy young adults receiving six manual therapy sessions consisting of rotational mobilizations above Th5 over 14 days. Feasibility outcomes included adherence, absence of unexpected adverse events (UAE), and practicality of autonomic data acquisition. Physiological outcomes comprised HRV parameters, high-frequency (HF), low-frequency/high-frequency ratio (LF/HF) and HR, analyzed using autoregressive (AR) and fast Fourier transform (FFT) methods. Results Procedural safety and methodological integrity were confirmed (no UAE; complete datasets), but feasibility was only partially achieved due to adherence shortfalls, higher attrition, and device-related delays. Physiologically, large effect sizes were observed in the intervention group: at evening assessment, HF_AR showed ES = 0.80 (p = .008); at morning assessment, HF_FFT ES = 0.72 (p = .016), HF_AR ES = 0.78 (p = .010), and LF/HF_AR ES = 0.70 (p = .021). HR remained unchanged. These findings suggest repeated TSM may modulate HRV, primarily through HF-related changes associated with vagal activity, while LF/HF interpretation remains controversial. Conclusion A randomized TSM protocol is safe and methodologically viable with logistical refinements. Preliminary evidence indicates potential vagal modulation, warranting larger trials with respiratory control, ECG-based HRV, multimodal ANS measures, and clinical populations to confirm efficacy and translational relevance.