Nervous system reset | How ice and heat support balance
- Megan Pleva
- Sep 12
- 4 min read
Updated: Oct 15
Nervous system 101: decoding your body’s stress signals
The nervous system is the body’s control centre. Every thought, movement, and emotional response is directed through a vast network of electrical signals that run between brain, spine, and body. It regulates both the voluntary, such as walking, lifting, and stretching, and the automatic, including heart rate and digestion.
The automatic side, known as the autonomic nervous system, has two distinct branches. The sympathetic nervous system activates “fight or flight” mode, priming you for immediate action. The parasympathetic nervous system does the opposite, switching the body into “rest and digest” mode, where repair and recovery take place.
Too often, modern life leaves us operating from a state of low-level sympathetic activation: quickened breathing, tense muscles, disrupted sleep. While helpful in short bursts, long-term activation carries consequences for health, mood, and resilience.
Fight or flight in daily life
Faster heart rate and shallow breath
Increased cortisol and adrenaline
Tense muscles, clenched jaw, tight shoulders
Poor digestion and disrupted sleep
Rest and digest as restoration
Slow, steady breathing
Lowered blood pressure and heart rate
Relaxed muscles
Improved nutrient absorption and cellular repair
Balance between the two is not optional - it is essential for wellbeing.
The science of switching state
Research shows that it is possible to guide the nervous system back into balance. Practices such as breathwork, grounding in nature, and deliberate exposure to heat and cold all stimulate the vagus nerve, a major pathway that activates the parasympathetic system.
This is not just anecdotal. Peer-reviewed studies have demonstrated that short-term cold exposure can increase parasympathetic activity after an initial sympathetic spike, while sauna use has been linked to reduced cardiovascular strain, improved circulation, and better stress regulation over time. Together, they form a cycle of activation and reset that trains the nervous system in adaptability.
Why contrast exposure works at ISKA
At ISKA, contrast exposure - alternating between ice bath immersion and infrared sauna - uses these natural mechanisms to full effect.
Cold immersion and the sympathetic spark
An ice bath is a controlled stressor. As you step in, the sympathetic nervous system fires: heart rate rises, breath quickens, adrenaline surges. This is the body’s instinctive survival response to the cold. But within minutes, with steady breathing and focus, the body adapts. Once you step out, parasympathetic rebound begins... heart rate slows, circulation improves, and calm sets in.
Heat exposure and parasympathetic depth
Infrared sauna works differently. The deep heat penetrates muscle tissue, dilates blood vessels, and reduces physical tension. Breathing slows naturally, and the body settles into parasympathetic dominance. This state enhances digestion, cellular repair, and mental clarity.
The mix: building resilience
Moving between extremes of ice and heat trains the nervous system to switch efficiently between sympathetic and parasympathetic modes. Over time, this builds flexibility - the ability to respond sharply to stress, then recover quickly. For athletes, this supports faster physical repair. For everyday life, it strengthens emotional resilience and sleep quality.
Practical ways to notice and reset
Awareness is the first step. Research in neurophysiology highlights the role of interoception - the ability to sense internal states like heart rate and breathing - in regulating stress responses. By tuning into these subtle cues, you can recognise which state your body is in and respond deliberately.
At ISKA. you can support this reset with practices during your session that are grounded in science:
Breathwork in the ice bath
Try a physiological sigh (two quick inhales through the nose, one long exhale through the mouth) to calm the nervous system during immersion. Breath control directly stimulates the vagus nerve, which links brainstem to organs throughout the body. Techniques such as the physiological sigh (two quick inhales followed by a slow exhale) have been shown in controlled studies to lower carbon dioxide levels, reduce heart rate variability, and enhance parasympathetic activation. Practising this during ice immersion allows the nervous system to shift more efficiently from sympathetic arousal to parasympathetic calm.
Intentional cooling and heating
Short bouts of cold exposure, typically two to four minutes, trigger a spike in norepinephrine and adrenaline, heightening alertness and constricting blood vessels. When followed by heat exposure of ten to fifteen minutes, vasodilation occurs, increasing circulation and nutrient delivery to tissues. Research from Finnish sauna cohorts shows regular use is linked to a reduced risk of cardiovascular disease and improved autonomic function. Alternating between cold and heat within an hour-long session amplifies this hormetic effect, a controlled stress that strengthens resilience.
Presence in the process
The practice is not only physical. Neuroscientific studies show that mindful awareness of bodily states strengthens prefrontal cortex regulation over the amygdala, the brain’s threat-detection centre. By consciously observing the shift from the shock of cold to the relaxation of heat, you are literally training the neural pathways involved in emotional regulation.
Finding balance in Bath
The nervous system thrives on balance, not extremes. Both sympathetic and parasympathetic responses are vital - one sharpens reaction time, the other enables restoration. Research on heart rate variability (HRV) confirms that flexible switching between these states is a key marker of health and longevity.
Cold water expsoure and sauna practice at ISKA provide a structured way to build this flexibility. Studies have shown that regular cold immersion improves dopamine release, supporting mood and motivation, while infrared heat increases heat shock proteins, aiding cellular repair and reducing inflammation. Together, these effects extend beyond the session - improving sleep, emotional resilience, and long-term stress tolerance.
In Bath, ISKA offers more than physical wellness. Our sessions retrain your body’s stress response, align with established scientific principles of autonomic regulation, and create a controlled environment for nervous system adaptability. This is where stress becomes strength, and wellness becomes resilience.
See you soon,
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