Everyone wants to know the recipe: How long should you cold plunge? How cold should the water be? How many times per week?
The recommended protocol is 10–15 minutes in water between 50 and 59 degrees Fahrenheit, two to three times per week.
But understanding how cold water immersion works, and how to do it safely, requires a deeper look at what happens in your body during those minutes in icy water.
How Cold Water Immersion Works
Cold water immersion triggers two distinct mechanisms in your autonomic nervous system.
First, we have what’s called the diving reflex. Receptors in the skin of your face and upper body trigger your parasympathetic nervous system to respond when you’re fully immersed in cold water. This ancient reflex helped our ancestors survive underwater.
Second, the initial shock of cold water creates a surge of sympathetic discharge. Your body responds with peripheral vasoconstriction, increased heart rate, and elevated blood pressure. Then, your body tries to compensate by triggering increased parasympathetic tone.
This back-and-forth between sympathetic activation and parasympathetic compensation is where cold plunging becomes what I call “parasympathetic rehab” or “homeostasis training.”
Rethinking the Autonomic Nervous System
For years, I’ve explained the autonomic nervous system using a teeter-totter metaphor: the sympathetic nervous system (fight or flight) on one side, the parasympathetic nervous system (rest and digest) on the other, and balance achieved in the middle.
But that metaphor has a flaw. It suggests equal symmetry on each side, as if both systems play equivalent roles in our health.
They don’t.
A better metaphor is a sailboat in stormy seas.
The sympathetic nervous system is the sail and mast. It propels you forward, but it’s also a toppling force. In a strong wind, the sail wants to knock the boat over. Sympathetic overload is associated with disease.
The parasympathetic nervous system is the weighted keel below the waterline. It anchors the boat and keeps it upright. Parasympathetic strength is associated with resilience to disease and the ability to maintain homeostasis.
This ties into aging and longevity. Aging is about homeostasis: our ability to rebalance after the inevitable buffeting of life.
As we age, we don’t right our sailboat as well. The parasympathetic nervous system degrades. Heart rate variability (HRV), our best real-time measure of the balance between sympathetic and parasympathetic tone, declines with age.
Keeping the sailboat upright allows us to age more successfully.
Cold water immersion strengthens your weighted keel. It trains your parasympathetic nervous system to respond more effectively to stress.
The Well-Supported Benefits
Cold water immersion has advantages across several areas, and the literature supports these benefits well.
Sports Recovery
Studies show a reduction in delayed onset muscle soreness (DOMS). Cold water immersion has demonstrated benefits in muscle performance during jumping and sprinting, as well as reduced markers of muscle damage in the blood.
Mental Health and Sleep
Cold water can improve feelings of stress and negative emotions. It can help with relaxation and sleep quality, which makes sense given our discussion about sympathetic and parasympathetic balance.
Metabolic Health
Cold water immersion can increase the energy your body uses, which may help with metabolism.
A small percentage of our total fat is brown fat. Unlike white fat, brown fat burns calories to generate heat. Cold water immersion activates these fat cells, which can increase your basal metabolic rate. Evidence suggests that overall metabolic health improves with cold water immersion: lower blood sugar, better insulin sensitivity.
Cold Plunging: The Dangers You Need to Know
Rapid sympathetic discharge followed by compensatory parasympathetic response can be dangerous. This is why understanding how long and how to cold plunge is necessary for safety.
Cold Shock
Cold shock occurs when your body is immersed in water below 59 degrees Fahrenheit. Anyone who has jumped into a cold lake has probably experienced this. It’s an involuntary set of reactions that can last from a few seconds to about a minute, peaking around 30 seconds.
During that minute, you gasp involuntarily. Your breathing rate increases — hyperventilation. Your heart rate shoots up rapidly. Blood pressure surges. Peripheral vasoconstriction occurs.
If you’re immersed underwater, it’s a real drowning risk. You involuntarily open your mouth. You could aspirate, or even drown.
If you have any risk factors for cardiac arrhythmia, this sudden buffeting by the sympathetic surge and parasympathetic compensation creates risk for dangerous heart rhythms.
As a backpacker, I’m acutely aware that at elevation (6,000–10,000 feet), the hypoxia in the air accelerates all this and compounds the potential risk of cold shock.
One of my daughter’s classmates died while swimming in a mountain lake. He was college-aged and very healthy. It was probably a cold shock reaction.
When I go backpacking with my kids and they want to swim in a mountain lake, I tell them to stay parallel to the shore and not try to swim across the lake. People underestimate the risks of cold water at elevation.
Who Shouldn’t Cold Plunge
So, how long should you cold plunge? For people with the following conditions, zero minutes and zero seconds:
- Heart disease or any cardiac problems
- Uncontrolled blood pressure
- Raynaud’s disease
- Asthma
- Neuropathy
- Pregnancy
- Recent surgery
Nobody should practice cold-water immersion alone in open water, regardless of health. Have others nearby.
How to Start Safely
When beginning cold water immersion, don’t start by instantly putting your head under the water. For the first minute, keep your head above the water.
Start with just one to three minutes, two to three times per week.
You’ll adapt to cold water immersion over time. Like anything, build up gradually. Over weeks and months, you can work toward the 10–15 minutes recommended in the literature. If at any point you experience chest discomfort, lightheadedness, numbness, or dizziness, abort the mission.
Once you finish your cold water immersion, don’t run straight to a hot shower. That’ll give your system too much stimulation in the other direction.
Warm up more slowly. Towel yourself off, maybe have a hot beverage. Let your body regulate its temperature gradually.
Cold Plunging: A Potent Tool, Not a Silver Bullet
Cold water immersion can be a wonderful tool for enhancing parasympathetic tone and recovery after intense workouts, but don’t think of it as a standalone modality or silver bullet.
It’s an arrow in the quiver: one tool among many in a more robust parasympathetic rehab program that includes meditation, careful attention to breathing, Zone 2 cardio, and other lifestyle interventions.
At Banner Peak Health, we look for every possible mechanism to strengthen the parasympathetic nervous system and enhance our patients’ resilience. Cold water immersion, practiced safely and as part of a comprehensive approach, can be a valuable addition to that program.
