The Physiological Menu
Thermal stress offers a unique opportunity to deliberately influence various physiological processes, enabling the development of personalized strategies to support a wide range of health and wellness goals. While longevity continues to be a central focus in today's health and wellness environment, exercise remains the most accessible and effective intervention for reducing all-cause mortality. More recently, contrast therapy, alternating between heat and cold exposure in a single session, has gained renewed attention for its comprehensive benefits. By leveraging physiological responses similar to those triggered by exercise and dynamic performance environments, contrast therapy and other forms of deliberate thermal stress promote resilience and systemic adaptation. In this article, I explore the scientific principles behind these practices, empowering you to make informed, evidence-based decisions when implementing thermal stress into your wellness plan.
The autonomic nervous system (ANS), composed of the sympathetic and parasympathetic branches, plays a central role in maintaining homeostasis by relaying sensory input and motor output between the body and the central nervous system (CNS). Functioning as a continuous feedback loop, the ANS influences nearly every physiological process in the body. Understanding the role of these systems in overall health is the first step toward effectively managing them. With deliberate control, individuals can optimize this system for intentional benefits. Whether aiming for cognitive improvements (such as increased energy and focus), psychological enhancements (such as improved mood), or physiological benefits (such as improved metabolic health and hormonal regulation), numerous practical tools are available for implementation. Controlled exposure to stressors, such as heat and cold, induces a hormetic response that promotes both physiological and psychological adaptation. These interventions, when applied strategically, can stimulate positive adaptations and promote optimal health that transfer beyond the specific environment in which they are implemented.
The sympathetic nervous system (SNS) is best known for initiating the "fight, flight, or freeze" response. This vital survival mechanism heightens alertness, increases arousal and primes the body for action during stressful situations. Often manifested as feelings of anxiety or nervousness, particularly when misunderstood or unexpected, it is a natural and adaptive physiological process. Importantly, our SNS can be trained and regulated through intentional practices. By learning to modulate sympathetic activation, individuals can harness its benefits to enhance both physical performance and cognitive function. In the following sections, we will explore how strategic upregulation of the SNS can be leveraged to support health and resilience, along with practical methods to optimize its effects. The parasympathetic nervous system (PNS), often called the "rest and digest" system, plays a vital role in restoring and maintaining physiological balance. It conserves energy by slowing the heart rate, supporting digestion, regulating hormonal activity, and relaxing smooth muscles in the gastrointestinal tract. Activation of the PNS is commonly associated with a calm, restorative state, making it an ideal physiological foundation for recovery strategies. We will also explore how intentionally down regulating through PNS activation can be leveraged to support health and resilience, along with practical methods to optimize its effects.
The stress response is a complex set of mechanisms designed to help the body adapt to challenges and restore internal homeostasis. This response is primarily regulated by the hypothalamic-pituitary-adrenal (HPA) axis and the above mentioned ANS, which coordinate the release of hormones (ie cortisol) and influence metabolism, immune activity, heart rate and blood pressure. At the cellular level, stress activates protective proteins which help minimize damage and support cellular repair. While acute stress is generally beneficial, chronic, unmanaged stress can contribute to immune suppression, physiological dysfunction and mental health issues. Importantly, not all stress is harmful. Eustress, or positive stress, plays a vital role in enhancing motivation, resilience and performance. Exercise, intermittent fasting and controlled exposure to heat or cold are among the commonly selected eustressors, triggering adaptive responses that ultimately strengthen the body and mind. Effectively leveraging these beneficial stressors while minimizing chronic distress is essential for supporting long term health and well-being.
Inflammation is a fundamental physiological response to external stressors, whether voluntary or involuntary, and plays a crucial role in the body’s defense and repair mechanisms. Inflammation remains a key focus in health and wellness assessments. Chronic inflammation is widely recognized as a key contributor to the development and progression of numerous diseases, including cardiovascular conditions, metabolic disorders, and neurodegenerative illnesses. While acute inflammation can be beneficial in specific contexts, chronic inflammatory states often go unrecognized or misunderstood. Gaining insight into the biomarkers associated with inflammation is essential to empower individuals to make targeted behavioral, dietary and supplemental adjustments aimed at restoring balance and reducing disease risk.
It is important to be aware that transient increases in inflammation are a natural byproduct of acute stress exposure and a fundamental part of the immune response. Suppressing, reducing or attempting to eliminate this temporary elevation would undermine the potential benefits of the stress response. However, chronic inflammation should be mitigated or eliminated to prevent adverse health outcomes. Despite being less visible, chronic inflammation plays a significant role in the development of various long term health conditions, including cardiovascular disease, diabetes and autoimmune disorders. When the stressor is positive and intentionally applied, such as appropriate training levels and controlled thermal stress duration, this period of heightened inflammation is associated with beneficial adaptive responses.
Common markers of inflammation can be reliably assessed through blood testing, offering valuable insights into the body’s internal physiological environment. Biomarkers such as C-reactive protein (CRP), interleukins (e.g., IL-6, IL-10), nuclear factor erythroid 2–related factor 2 (Nrf2), cortisol and blood glucose serve distinct diagnostic roles in evaluating the inflammatory response and the body’s capacity to adapt to stress. Collectively, these indicators provide a comprehensive view of systemic inflammation and resilience to both environmental and physiological stressors.
Cytokines are powerful proteins that regulate immune activity and inflammation throughout the body. Among the most well-known are interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-alpha (TNF-α). While these cytokines are essential in responding to acute threats, chronically elevated levels are linked to various diseases, including cardiovascular disease, autoimmune disorders and metabolic syndrome. Acute phase proteins are rapidly produced in response to inflammation. CRP levels increase significantly during inflammatory processes, making it a valuable biomarker for detecting systemic inflammation. Clinically, CRP is commonly used to assess the risk of cardiovascular events, as elevated levels are associated with a higher likelihood of heart attacks, strokes and other cardiovascular conditions. Additionally, hsCRP is particularly useful in assessing cardiovascular risk in otherwise healthy individuals, as elevated hsCRP levels have been linked to an increased risk of atherosclerosis and other cardiovascular diseases.
Regular sauna use has been shown to increase white blood cell counts and fibrinolytic activity, enhancing immune function and reducing systemic inflammation, respectively. Additionally, sauna-induced sweating leads to electrolyte loss, which can temporarily affect the sodium/potassium ratio, a useful indicator of the body’s inflammatory state. Proper hydration and electrolyte replenishment after sauna sessions are essential for maintaining physiological balance. Collectively, these systemic effects stimulate the activation of the hypothalamic-pituitary-adrenal (HPA) axis in response to stress. When activated, the HPA-axis triggers the release of corticotropin-releasing hormone (CRH), stimulating glucocorticoid secretion from the adrenal glands. These hormones play dual pro-inflammatory and anti-inflammatory roles in the body. Together, these adaptations strengthen sauna's theraputic potential to modulate stress and immune pathways, contributing to improved health outcomes and disease prevention.
Thermoregulation is the body's ability to maintain a stable internal temperature, a process primarily governed by the medial peoptic area (POA) of the hypothalamus. This brain region play a critical role in both thermal balance and sleep regulation. Everyone has a baseline core body temperature that follows a natural circadian rhythm, typically decreasing in the even and during sleep, then rising approximately two hours before waking. The body regulates temperature across two main zones. The first, core temperature, which include vital organs and the central nervous system. The second, skin (or shell) temperature, which the brain continuously monitors, functioning much like a thermostat. In response to internal or external thermal shifts, the POA activates mechanisms such as sweating, vasodilation and brown adipose tissue thermogenesis. Controlled exposure to heat or cold can influence this circadian rhythm and stimulate these natural responses, offering a powerful tool to support overall health, performance and stress resilience.
Sauna use supports the body through several interconnected physiological processes that promote health, recovery, and long-term resilience. One notable effect is the increased availability of nitric oxide, a compound that helps relax and widen blood vessels, leading to improved blood flow and cardiovascular function. The heat also stimulates the production of heat shock proteins, which assist in cellular repair, regulate metabolism, and enhance the body’s ability to adapt to stress. In addition, sauna use has been shown to influence immune and hormonal activity, helping the body recover more efficiently and become more resilient to both physical and emotional stressors. The heavy sweating induced during a sauna session also plays a role in detoxification by supporting the excretion of stored toxins. On average, an individual may lose approximately 0.5 kilograms of sweat per session, highlighting sauna a potential detoxification tool. These responses activate a process known as hormesis, beneficial adaptations triggered by short-term, manageable stress, that ultimately help strengthen the body and support overall well-being.
Heat-shock proteins (HSPs) are present in all cells and play crucial roles in immune function, cell signaling and cell life cycle regulation. Under normal conditions, cells maintain a baseline level of HSPs to support protein production, folding and turnover. However, when the body faces stress, such as from extreme temperatures, the expression of HSPs increases to help protect and repair damaged or misfolded proteins to prevent further damage and aggregation. This process is essential for maintaining protein integrity and supporting overall cellular health. Research also suggests that HSPs may offer neuroprotective benefits by reducing amyloid plaque buildup, which is associated with neurodegenerative diseases. The heat shock response activates the body’s protective mechanisms to repair and stabilize proteins. Following internal thermal stress via the sauna, HSP levels remain elevated for up to 48 hours and offer continued protection. By strategically exposing the body to stressors such as heat or fasting, the increased expression of HSPs helps stabilize impaired proteins, reduce damage, and improve cellular resilience supporting overall health and well-being.
It is essential to align health practices with the conditions under which their benefits were scientifically validated. For example, while sauna use is associated with numerous health advantages, failing to meet the specific thresholds for temperature, duration, or frequency may result in suboptimal outcomes and diminish the intended benefits. Having said that, research consistently supports the use of traditional dry saunas operating at temperatures between 176°F to 212°F (80°C and 100°C) with low humidity as an effective strategy for promoting cardiovascular and overall health. Research has shown individuals using a sauna 2–3 times per week experience approximately a 24% reduction in all-cause mortality, while those using it 4–7 times per week see a reduction of up to 40%. These findings highlight sauna bathing as a potent, non-invasive health intervention when practiced regularly. These benefits are dose-dependent, meaning the more frequently you use the sauna, the greater the impact on your health.
Regular sauna use has also been linked to a reduced risk of neurodegenerative diseases and increased longevity. One proposed mechanism involves the upregulation of FOXO3, a protein that plays a critical role in DNA repair and the removal of damaged or senescent cells. Research indicates that individuals with naturally elevated FOXO3 levels or specific genetic variants are approximately 2.7 times more likely to live past 100 years of age. Notably, sauna exposure can stimulate FOXO3 expression, potentially offering similar neuroprotective and longevity promoting effects, even in those without a genetic predisposition.
Beyond physical detoxification, sauna use also appears to influence neurochemical pathways involved in mood regulation. Voluntary heat exposure through a sauna session activates the release of endorphins. Endorphins, the well known "feel good" chemical produced in response to acute stress, has been shown to enhance mood and promote a sense of well-being. In addition to triggering endorphin release, heat exposure from sauna use also stimulates the production of dynorphins. Following initial feelings of discomfort, dynorphins are responsible for the subsequent adaptation responsible for increasing the sensitivity and number of mu-opoid receptors, which are the main targets of endorphins. As a result, future endorphin release has a stronger effect, contributing to greater mood enhancement and a more sustained sense of well-being. This process may help explain why regular sauna users often report improved mood, elevated baseline happiness and better overall mental health.
Cold exposure triggers a robust stress response, significantly increasing the release of catecholamines such as epinephrine (adrenaline), norepinephrine (noradrenaline), and dopamine. This surge enhances alertness, energy, and cognitive function, with effects lasting approximately 4 to 6 hours. Cold water immersion can elevate adrenaline and noradrenaline levels by 200–500%, activating the sympathetic nervous system and sharpening focus. Dopamine levels may increase by up to 250%, contributing to improved mood, motivation, and sustained mental clarity. In addition to these neurochemical shifts, cold exposure also stimulates the production of cold shock proteins, promoting mitochondrial biogenesis. Collectively, the hormetic effect as a result of cold water immersion leads to enhanced mental and physical performance.
Endogenous protein stimulation as a result of cold exposure has been shown to activate brown adipose tissue (BAT). Once believed to exist only in infants, BAT in adults plays a key role in regulating metabolism by burning fat to generate heat. Regular, whole-body cold exposure can improve glucose and lipid metabolism, reduce inflammation, enhance cognitive function, and boost immune health, all of which are highly critical components of overall well-being. While cold exposure can be uncomfortable, calming techniques (physiological sigh, cadence breathing, etc) can help individuals endure it, further strengthening resilience by allowing the body to adapt to stress.
By implementing simple strategies to maximize benefits while minimizing potential drawbacks, individuals leverage these physiological processes in practical, impactful ways. For example, when utilizing cold water immersion, applying the Soeberg Principle can be an effective approach for dual cognitive and metabolic effect. This strategy is often best used in the morning hours. Alternatively, ending a session with heat in the evening can help avoid the stimulatory effects of catecholamines and resulting energy levels that might interfere with sleep for some individuals. This approach retains the previously discussed comprehensive benefits while adding the thermoregulatory effect of decreasing internal body temperature, an advantageous approach to improving sleep quality. These strategies help optimize the cognitive and physiological benefits of contrast therapy, while also supporting the maintenance of a healthy circadian rhythm and mitigating any potential disruption to essential processes, such as sleep.
When prioritizing performance and/or body composition, research indicates that post-exercise inflammation plays a significant role in mediating exercise adaptations. Immediately following exercise, blood concentrations of pro-inflammatory proteins and reactive oxygen species increase. In contrast, concentrations of anti-inflammatory proteins typically peak within the first hour post-exercise, likely limiting the magnitude and duration of the initial inflammatory response. These physiological responses contribute to the beneficial adaptations induced by exercise. However, excessive exercise-induced inflammation can result in muscle damage, fatigue, and immune dysfunction, with the extent of these effects depending on the duration and intensity of the exercise. Cold exposure immediately after exercise may interfere with the beneficial training adaptations, including exercise induced low-grade inflammation, by blunting the immune response. The peak anti-inflammatory response generally occurs within an hour post-activity, suggesting that some level of inflammation and immune activation during the early recovery phase may be beneficial.
The effects of cold exposure on athletic performance and recovery vary depending on timing, method and training type. Research suggests that immediate cold water immersion after resistance training impairs muscle growth by suppressing protein synthesis and reducing anabolic signaling pathways, such as satellite cell activation, mTOR signaling and ribosomal biogenesis. However, delaying cold exposure has been associated with reduced soreness and improved performance markers, without sacrificing they hypertrophic adaptations associated with resistance training. Given the current evidence, caution is advised when applying cold exposure immediately after strength training, especially when muscle hypertrophy is a primary goal.
The following protocols represent evidence-based minimum thresholds shown to elicit the most significant health benefits. They are designed to offer flexibility, accommodate personal preferences, and allow for varying levels of challenge depending on individual goals, time constraints, and lifestyle factors. While these examples apply the core principles, many alternative approaches can provide comparable outcomes, as long as the scientifically supported thresholds are achieved within each session.
*While there is no universally prescribed temperature for cold water immersion, the water should be cold enough to cause discomfort, yet tolerable enough to remain in safely. For most individuals, this therapeutic range typically falls between 50–56°F (10–13°C), though beginners or those particularly sensitive to cold may benefit from slightly warmer temperatures initially. You will likely adapt to the cold temperatures, further requiring colder exposures to achieve the same physiological effects. Notably, even a brief break from cold immersion can reset tolerance, making the experience feel as challenging as the first time. As a general guideline, if the water makes you want to get out, but you can remain in safely with controlled effort, you're likely within the effective therapeutic range. 
By understanding the underlying mechanisms and principles of deliberate thermal stress, individuals can make more informed and confident decisions about how to incorporate deliberate heat and cold use in a way that aligns with their personal health goals, preferences and lifestyle. Implementing flexible strategies, whether daily, weekly, or monthly, tailored to one's goals enables the creation of a structured and sustainable routine. When approached this way, thermal stressors become a powerful complementary health practice, offering unique benefits that are best realized when used alongside, rather than in place of, other foundational wellness strategies. The physical and psychological benefits of intentional thermal stress is as close to a one size fits all health tool that is readily available to everyone. As Dr. Ethan Kross states regarding the ability to intentional manipulate one's state, whether physical or mental, "this knowledge is critical, because when you know, you can play with these levers."
