Temperature Training & Stress inoculation

Cold plunges. Sauna selfies. "Mental toughness" ice tubs in every gym.

Temperature training is having a moment and like most wellness trends, the hype is running a little ahead of the data.

This newsletter breaks down what we actually know about:

• Heat (sauna, heat acclimation)

• Cold (cold plunges, ice baths, cold showers)

• “Stress inoculation,” hormesis, and the HPA axis

• Who should do it, how often, and how to do it safely

• What really translates to resilience and performance

1. Temperature training 101: What are we trying to do?

“Temperature training” = deliberate exposure to heat or cold at doses high enough to be uncomfortable, but not dangerous, with the intent to:

• Improve cardiovascular and metabolic health

• Enhance stress tolerance / HPA-axis flexibility

• Build psychological resilience (“I can stay calm under discomfort”)

• Possibly support recovery and sleep when used appropriately

Mechanistically, both heat and cold are hormetic stressors: small, repeated challenges that push the system just enough to trigger adaptation (e.g., heat shock proteins, changes in autonomic balance, improved vascular function) (Belity et al., 2022).

2. Physiology in plain language: Heat vs. cold

Heat (sauna, heat acclimation)

What happens in the body:

• Skin and core temperature rise → vasodilation → heart rate increases to ~moderate exercise levels (Laukkanen et al., 2018).

• You sweat more efficiently over time, plasma volume expands, and your cardiovascular system gets better at handling heat stress (heat acclimation) (Donnan et al., 2023).

• Heat stress induces heat shock proteins (HSPs), including HSP-70, which help protect cells from future stress and may support behavioral resilience in animal models.

Key outcomes from human studies:

• Regular sauna use (2–7x/week) is associated with lower cardiovascular mortality and sudden cardiac death in large Finnish cohorts.

• Short-term interventions combining exercise + sauna improve vascular function and blood pressure in randomized trials (Lee et al., 2022).

• Heat acclimation protocols (5–10 days of repeated heat exposure) improve exercise capacity and mitigate cognitive deficits in the heat.

Heat is a controlled way to practice staying engaged while physiologically uncomfortable, while also driving real cardiovascular and thermoregulatory adaptations.

Cold (cold plunge, ice baths, cold showers)

Acute response:

• Cold shock → rapid sympathetic activation (spike in HR, blood pressure, norepinephrine). Followed by parasympathetic rebound when out of cold (Espeland et al., 2022).

• Repeated exposures shift brown fat activity, thermogenesis, and some metabolic markers.

Neurochemical & mood data:

• Cold-water immersion (CWI) acutely increases norepinephrine, dopamine, β-endorphin, and cortisol; repeated exposures may blunt cortisol reactivity and enhance subjective well-being (Lopez-Ojeda & Hurley, 2024).

• A 2025 systematic review (Cain et al., 2025) finds CWI has time-dependent benefits for inflammation, stress markers, sleep, and quality of life, but emphasizes that most studies are small, heterogeneous, and not all are RCTs. 

• A single cold-water immersion in young healthy adults significantly improved mood (lower tension, anger, fatigue) (Kelly & Bird, 2021).

Cold exposure follows a hormetic pattern: acute HPA activation (cortisol spike), with potential longer-term “neurohormetic” recalibration of stress systems if well-dosed.

Localized cold (cold face test) can activate the vagus nerve, reduce cortisol responses to a psychosocial stress task, and blunt overall HPA output in the lab (Richer et al., 2022).

3. What actually translates to resilience?

Important distinction:

• Physiological resilience = more efficient cardiovascular / thermoregulatory / HPA response (faster recovery, less total cortisol exposure).

• Psychological resilience = ability to maintain effective behavior and mindset under stress.

The evidence is strongest that:

• Heat acclimation improves tolerance and performance in hot environments, and may mitigate some cognitive impairment under heat stress.

• Cold-water exposure can improve mood and perceived stress and may modulate inflammatory and hormonal markers over time.

• Both act as “training reps” for discomfort, giving you practice at noticing stress, controlling breath, and directing attention while the body is screaming “GET OUT.”

But: direct RCT evidence that sauna or cold plunges make you more resilient to unrelated life stressors (e.g., high-stakes meetings, competition pressure) is still limited. Most of that link is conceptual (hormesis + HPA flexibility) and extrapolated from related data (e.g., exercise-induced HPA adaptations, heat/cold stress markers).

So you can think of temperature training as a supportive tool, not a magic inoculation.

4. Sex differences: Do males and females respond the same?

Short answer: not exactly. And most research has been done in men.

Heat

• A 2021 review on heat acclimation finds that most data are male; limited evidence suggests females may require more sessions or greater thermal load to achieve the same degree of adaptation (Wickham et al., 2021).

• Classic sauna studies show greater ACTH and prolactin responses in women vs. men during heat and cold-pressor tests, suggesting sex-specific neuroendocrine patterns under thermal stress (Jezova et al., 1996).

Practical implication: Women may respond strongly at the hormonal level and might benefit from slightly more gradual progression, especially across different menstrual phases or in perimenopause.

Cold

• Short-term cold exposure shows some hormonal and metabolic responses are more pronounced in women, even when overall thermogenic response is similar (Mengel et al., 2020).

• Other work suggests similar catecholamine and cortisol responses to ice baths in men and women, with time-of-day influencing cortisol more than sex (Braunsperger et al., 2025).

Big picture:

• Men and women both adapt to heat and cold, but patterns of hormonal response differ.

• Women are historically under-represented in studies, so protocols are less "validated" in female populations, especially high-intensity exposures.

For female high performers, this argues for:

• More conservative starting doses

• Respecting cycle-related fluctuations (energy, mood, temperature sensitivity)

• Extra caution if pregnant, postpartum, or with endocrine conditions (medical clearance is non-negotiable there).

5. Who should not be playing with extreme heat/cold?

Temperature training is not a good idea (without careful medical clearance) if you have:

• Unstable or significant cardiovascular disease (e.g., recent MI, unstable angina, uncontrolled arrhythmias)

• Poorly controlled hypertension

• History of syncope, serious autonomic dysfunction, or severe orthostatic intolerance

• Raynaud’s disease or severe peripheral vascular disease (for cold)

• Pregnancy (especially very hot sauna / hot tubs)

• Underlying conditions affecting temperature regulation (e.g., some neurological disorders)

Even for healthy high performers, start conservatively, avoid training alone, and avoid alcohol/dehydration before sauna or cold plunges.

(Standard disclaimer: this is educational, not medical advice. Talk to a clinician who knows your history.)

6. How to do it: Best-practice protocols (based on current data)

A. Heat / sauna for performance & resilience

Evidence-based ranges (from RCTs and cohort data):

• Temperature: 70–90°C (158–194°F), typical Finnish sauna.

• Duration per bout: 10–20 min (~30 min max), 1–3 rounds with cool-down in between optional.

• Frequency:

  • Health & cardiovascular benefits: 2–4x/week is common in the data.

  • Heat acclimation for sport: 5–10 consecutive days of 30–60 min heat exposure (exercise in heat for up to 60 min. or 30 min-post-exercise sauna) at a tolerable but challenging level.

For high performers:

• Athletes in hot environments:

  • Use sauna or training in heat 1–2x/day for ~7–10 days leading into competitions in hot climates.

  • Monitor body weight, hydration, HR, and subjective strain.

• Executives/coaches:

  • 10–20 min sauna 2–4x/week after a light workout or at the end of the day can support cardiovascular health and provide a structured “discomfort + unwind” window.

Do NOT:

• Push past dizziness, chest pain, confusion, or nausea.

• Combine aggressive sauna with heavy dehydration, alcohol, or extreme fasting.

B. Cold exposure for mood, stress, and “mental reps”

The data on exact dosing are much more variable, but patterns are emerging.

Evidence-informed ranges:

• Water temperature: commonly 8–15°C (46–59°F) in studies.

• Duration: 1–5 minutes per immersion for whole-body CWI; briefer (30–60 sec) is reasonable for new users.

• Frequency:

  • Many studies use 2–5 exposures/week over several weeks for mood/stress outcomes.

For high performers:

• Start with cold showers: 30–60 s at the end of a warm shower, 3–4x/week.

• Progress to short immersions (e.g., 1–2 min at 12–15°C), up to 3–4x/week if well tolerated.

• Focus on:

  • Calm nasal breathing 

  • Relaxed jaw/shoulders

  • Keeping your attention on task or chosen cue, not on catastrophizing the discomfort

When NOT to cold plunge:

• Immediately pre-strength or hypertrophy workouts if you care about muscle growth; some evidence suggests CWI can blunt anabolic signaling when used right after lifting.

• If you have uncontrolled hypertension or cardiovascular disease (due to transient BP spike).

If your main goal is mental resilience:The best “dose” is short, repeatable exposures that challenge but don't overwhelm your system. If you’re bracing, panicking, or taking hours to feel normal after, the dose is too high.

7. How often? Putting it into a weekly plan

For a healthy high performer, ballpark:

• Heat focus block (e.g., pre-season camp in the heat):

  • 5–10 days: daily heat exposure (sauna or training in heat), 30–60 min total at a challenging but safe intensity.

• Maintenance / general health & stress:

  • Sauna: 2–4x/week, 10–30 min per session.

  • Cold: 2–4x/week, 1–5 min CWI or 30–90 s cold shower.

For many busy execs and coaches, a sustainable combo is:

• 2x/week: workout → 10–15 min sauna

• 2–3x/week: short cold exposure (shower or plunge) as a "mental rep" and alertness boost

Always treat  sleep, training, and nutrition as the “big rocks.” Temperature work is a useful accessory, not the foundation.

8. “Should I do this?” A quick decision framework

Ask yourself:

1. Goal:

   • Hot environment performance? → prioritize heat acclimation.

   • Mood, energy, “mental edge”? → cold + heat both have roles, with cold particularly impactful on acute mood.

   • Cardiometabolic health? → strongest long-term data currently favor sauna.

2. Health status:

   • Any cardiovascular, endocrine, pregnancy, or autonomic issues? → get clearance.

3. Bandwidth:

   • If you’re already under heavy life/workload, start with 1–2 short sessions/week and focus on quality of attention and breathing, not intensity of suffering.

4. Psychological angle:

   • Use sessions as deliberate practice:

     • Notice stress signals

     • Regulate breath

     • Choose a helpful focus (e.g., cue word, gratitude, game plan)

   • That’s the part that transfers to game day, hard conversations, or clutch moments, more than the temperature itself.

9. Key takeaways for high performers

• Heat and cold are legit physiological stressors, not just “biohacks.”

• Sauna / heat: best evidence for cardiovascular benefits and heat tolerance; also a powerful mental-resilience playground.

• Cold exposure: promising for mood, perceived stress, and some inflammatory/metabolic markers, but long-term mental resilience effects are still being clarified.

• The HPA axis and autonomic system adapt to repeated, well-dosed stressors, but the goal is efficiency, not chasing maximal shock.

• Sex differences matter: women are under-studied and may show different hormonal responses and adaptation timelines, so progressive dosing and individualization are crucial.

If you treat temperature training like you treat physical training: specific goal, appropriate dose, room for recovery, and respect for your individual physiology, it can be a powerful adjunct to your performance and resilience toolkit.