What is Sympathetic Nervous System?
The sympathetic nervous system (SNS) is one of the two main branches of the autonomic nervous system. It is often summed up as "fight or flight": it speeds the heart, strengthens its contractions and mobilises the body for action.
Key Effects
- •Faster heart rate and stronger heart contractions
- •Blood flow redirected towards working muscles
- •Adrenaline released from the adrenal glands
- •Slowed digestion
- •Wider pupils, more sweating
Not a switch
The sympathetic and parasympathetic branches are not two ends of one dial. They can be active at the same time and can change independently, so "autonomic balance" is a shorthand, not something a single number such as the LF/HF ratio can read. Cortisol, the main stress hormone, is not released by this branch: it is regulated by the hormonal hypothalamic–pituitary–adrenal axis.
In ONDA Life
ONDA does not measure sympathetic activity. Its practices use slow, guided breathing, and the app reads heart rhythm, not the state of the nervous system.
Scientific Basis
See The Autonomic Nervous System for the full picture and sources.