Transcutaneous vagus nerve stimulation and exercise-induced autonomic regulation: a systematic review

To synthesise current evidence regarding whether transcutaneous vagus nerve stimulation modulates autonomic recovery following exercise-induced physiological stress in healthy individuals, with particular emphasis on vagal reactivation, spontaneous cardiovagal baroreflex sensitivity, sympathetic modulation and inflammatory responses.

This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 statement and registered in the Open Science Framework. Six electronic databases were searched. Fifteen randomised controlled trials involving 566 participants met inclusion criteria. Methodological quality, risk of bias and certainty of evidence were evaluated using the Physiotherapy Evidence Database scale, the revised Cochrane Risk-of-Bias tool and the Grading of Recommendations Assessment, Development and Evaluation framework.

Transcutaneous vagus nerve stimulation was associated with protocol-dependent modulation of autonomic recovery dynamics following exercise-induced physiological stress. Several studies reported changes consistent with enhanced vagal reactivation, reflected by increases in selected vagally mediated heart rate variability indices and improvements in spontaneous cardiovagal baroreflex sensitivity, alongside reductions in sympathetic activity in selected protocols. However, autonomic responses were not uniform across studies, with some investigations demonstrating null or divergent findings depending on stimulation parameters, timing and participant characteristics. Repeated stimulation paradigms demonstrated reductions in selected inflammatory markers, whereas acute stimulation occasionally induced transient cytokine elevations, suggesting context-dependent autonomic-immune interactions. Effects on maximal physical performance remained limited and inconsistent. Certainty of evidence ranged from very low to low, primarily because of methodological heterogeneity, small sample sizes and short follow-up durations.

Current evidence suggests that transcutaneous vagus nerve stimulation may influence autonomic mechanisms involved in recovery from exercise-induced stress, particularly processes related to vagal regulation, spontaneous cardiovagal baroreflex responsiveness and autonomic recalibration. Nevertheless, substantial heterogeneity in stimulation protocols and outcome assessment limits definitive interpretation. Larger, rigorously controlled and longitudinal investigations using standardised autonomic assessment methodologies are required to clarify the consistency, magnitude and physiological relevance of these effects.

The review protocol was registered in the Open Science Framework (OSF; https://doi.org/10.17605/OSF.IO/H9VRX ).