Theories of arousal predict a link between heart rate variability and reactive aggression: meta-analytic results disagree

Polyvagal theory posits that habitually aggressive individuals might have an impaired capacity to calm after arousal, which has led to the investigation of Arousal-based biological indicators - “biomarkers” - of aggression, to identify individuals at high risk. The most popular approach in research examining (specifically reactive) aggression is the use of wearable technologies that can non-invasively measure heart rate variability (HRV), a cardiovascular phenomenon impacted by activation of the parasympathetic (“rest and digest”) nervous system. But there is a problem: no one has systematically analyzed the results of these studies to determine if HRV is an effective predictor of reactive aggression. We surveyed an initial 705 articles, producing 48 effect estimates amenable to meta-analysis. Counter to predictions derived from polyvagal theory, the results reveal no correlation between HRV and reactive aggression. We discuss the implications of this novel finding for theory and practice, considering both the complexity of identifying effective biomarkers and the practical limitations driving methodological decisions in aggression research. We conclude that there is no empirical evidence supporting HRV as a valid biomarker of aggression.