The Parasympathetic Nervous System
The parasympathetic nervous system—often called the “rest and digest” system—plays a vital role in keeping the body balanced. Learning how to intentionally activate it can profoundly impact your physical health, mental well-being, and resilience to stress.
What Is the Parasympathetic Nervous System?
The parasympathetic nervous system is one of two branches of the autonomic nervous system, which controls involuntary functions like heart rate, breathing, and digestion.
Sympathetic nervous system: Triggers the “fight or flight” stress response.
Parasympathetic nervous system: Promotes relaxation, recovery, and homeostasis.
In the simplest terms:
Parasympathetic = relaxed self
Sympathetic = stressed-out self
The two systems work together to keep your body in balance, but in today’s high-stress world, many people get stuck in sympathetic overdrive—leading to fatigue, inflammation, and a higher risk of chronic disease [1].
Regulating Heart Rate and Breathing
The parasympathetic system slows the heart rate via acetylcholine, a neurotransmitter that tells the heart’s pacemaker cells to maintain a slower, steadier rhythm. It also reduces the force of contractions, allowing the body to rest.
For breathing, the parasympathetic system engages the diaphragm and other respiratory muscles to promote slower, deeper breaths—helping shift you into a calmer state.
Balancing the Stress Response
Under stress, the sympathetic nervous system raises heart rate, quickens breathing, and floods the body with stress hormones like cortisol and adrenaline. This is helpful short-term, but long-term sympathetic dominance can harm digestion, cardiovascular health, and mental well-being.
Activating the parasympathetic system helps counter these effects—slowing the heart, deepening the breath, and restoring balance to the nervous system.
How Sauna Activates the Parasympathetic Nervous System
Sauna bathing influences both branches of the autonomic nervous system, but its relaxation benefits come from the parasympathetic side. Heat and humidity promote vasodilation (widening of blood vessels), improving circulation, lowering blood pressure, and reducing heart rate.
Research shows sauna sessions can:
Lower stress hormones like cortisol and adrenaline [2]
Stimulate endorphin release for mood elevation [3]
Promote deep physical and mental relaxation
It’s a double benefit—heat stress triggers feel-good chemicals while also calming the nervous system.
How Cold Plunging Activates the Parasympathetic Nervous System
Cold plunging takes a different path to the same destination. Initial immersion sparks the cold shock response, activating the sympathetic nervous system—heart rate spikes, breathing quickens, and blood vessels constrict to preserve core heat.
Then, as the body seeks equilibrium, the vagus nerve helps shift the body toward parasympathetic dominance—slowing heart rate, deepening breath, and restoring calm. This controlled transition trains the body to recover from stress more efficiently, improving resilience over time.
Why It Matters
We’re biological machines made of soft tissue, and like any system, we run better when maintained. By understanding your autonomic nervous system and how to influence it—through practices like sauna, cold plunging, deep breathing, or meditation—you can better manage stress, enhance recovery, and protect long-term health.
Sources:
Fisher JP, Young CN, Fadel PJ. Auton Neurosci. 2009;148(1–2):5–15. doi:10.1016/j.autneu.2009.02.003.
Żychowska M, et al. Ann Agric Environ Med. 2017;24(1).
Laatikainen T, et al. Eur J Appl Physiol. 1988;57:98–102.