taVNS During Exercise and Recovery in Chronic Spinal Cord Injury

Spinal cord injury (SCI) is associated with significant impairments in autonomic nervous system function, particularly affecting cardiovascular regulation. These alterations reduce physiological adaptability to internal and external stressors and may contribute to increased cardiovascular risk. Transcutaneous auricular vagus nerve stimulation (taVNS) is a non-invasive neuromodulation technique that has been proposed as a potential tool to influence autonomic function. However, its effects on dynamic autonomic regulation during physiological stress, such as exercise, remain insufficiently characterized in individuals with SCI. The present study is a randomized, controlled, crossover experimental protocol designed to investigate the acute effects of taVNS on autonomic cardiovascular dynamics during a structured exercise and recovery paradigm. Participants with chronic SCI are exposed to two conditions: active taVNS and sham stimulation, applied in a randomized order. Each experimental session includes three phases: baseline (rest), exercise (submaximal effort), and recovery. Continuous electrocardiographic recordings are obtained to derive heart rate variability (HRV) metrics. Both linear (time and frequency domain) and non-linear analyses are performed to characterize autonomic regulation and system dynamics. The primary objective is to evaluate whether taVNS modulates autonomic responsiveness and adaptability across different physiological states. Secondary objectives include the exploration of HRV-derived biomarkers that may reflect autonomic complexity and the identification of response patterns to neuromodulation. This study is not designed to evaluate clinical efficacy or therapeutic outcomes but to provide mechanistic insight into autonomic regulation and neuromodulation effects in SCI. The results may contribute to the development of personalized approaches in neurorehabilitation and autonomic monitoring.