# Sympathetic dominance

Sympathetic dominance is when your nervous system gets stuck in 'go' mode. The fight-or-flight (sympathetic) side chronically outweighs the rest-and-digest (parasympathetic) side. You can see it in a few signs. Heart-rate-variability numbers like RMSSD and HF power drop. Resting heart rate rises. And the normal nighttime calming of vagal tone is blunted. A short burst of sympathetic activation is healthy. But staying elevated is not. It can come from psychological stress, overtraining, poor sleep, or metabolic problems. And it is tied to high blood pressure, a dysregulated stress-hormone (HPA) axis, and faster cardiovascular aging. It is not a medical diagnosis. It is a working concept used in longevity and sports science to flag poor autonomic recovery. Reading it right means ruling out confounders like dehydration, illness, and measurement glitches.

## Sources

- Malik M, Bigger JT, Camm AJ, et al.. (1996). Heart rate variability: Standards of measurement, physiological interpretation, and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. European Heart Journal. https://doi.org/10.1093/oxfordjournals.eurheartj.a014868
- Thayer JF, Lane RD. (2007). The role of vagal function in the risk for cardiovascular disease and mortality. Biological Psychology. https://doi.org/10.1016/j.biopsycho.2005.11.013

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