Hot + Cold: How Contrast Therapy Helps Your HRV

Written By Caleb Fritz

People around the world have been switching between hot and cold for centuries—saunas, cold rivers, hot springs, icy dips. Today we call it contrast therapy, and modern research is showing exactly why it works: it boosts a key marker of long-term health called HRV.

Here’s the easy version of what that means.

What Is HRV? (Simple Version)

Heart Rate Variability (HRV) is the tiny difference in time between each heartbeat.
A healthy heart does not beat like a metronome—it changes slightly depending on what your body needs.

Think of HRV like your “body adaptability score.”

  • Higher HRV = more flexible, more resilient, more tolerant to stress

  • Lower HRV = less adaptability, more worn down, more stress on your system

Your HRV changes with:

  • Age

  • Fitness

  • Stress

  • Sleep

  • Recovery

  • Even the time of day

The most helpful thing you can do is track your own baseline, not compare yourself to others.

HRV Red Flags (super simple):

  • Always low (under ~20ms)

  • Sudden big drop from your normal

  • No variation day to day

  • Doesn’t improve when you rest

If that’s happening, it usually means your body is under more stress than it can handle.

Why Contrast Therapy Helps HRV

Contrast therapy = Heat → Cold → Heat → Cold

These temperature swings train your nervous system the way a workout trains your muscles.

What Heat (Sauna) Does:

  • Activates your parasympathetic system (rest + recover)

  • Opens your blood vessels

  • Improves circulation

  • Boosts “heat shock proteins” (helps cell repair)

  • Helps blood sugar + insulin sensitivity

What Cold (Plunge) Does:

  • Activates the sympathetic system (wake up + focus)

  • Releases norepinephrine + dopamine (energy + focus chemicals)

  • Activates brown fat (burns energy, heats your body)

  • Strengthens your vagus nerve (big part of HRV)

  • Boosts immune function

The Magic Is the Back-and-Forth

Alternating hot and cold creates a healthy “stress workout” called hormetic stress.
Your body learns how to switch between calm and alert faster and more efficiently.

This leads to:

  • Better nervous system balance

  • Faster recovery

  • Higher stress tolerance

  • Stronger heart + blood vessels

  • Better HRV readings over time

How to Start Contrast Therapy (Easy + Safe Version)

Beginner Tips

  • Keep temperatures moderate

  • Start slow (10–15 min heat → 1–2 min cold)

  • Listen to your body

  • Stay hydrated

  • Check with your doctor if you have conditions or concerns

As You Progress

  • Slowly increase heat + cold times

  • Try different temperatures

  • Add breathing work

  • Track HRV with WHOOP/Garmin/Oura

  • Experiment with timing (morning, post-workout, stress relief)

How to Know It’s Working

Don’t obsess over daily numbers.
Instead, look for trends:

  • HRV slowly rising

  • More variation day to day

  • Faster recovery after workouts

  • Less stress on your baseline

  • Better sleep and energy

The goal is progress, not perfection.

Extra Benefits People Notice

Most regular users also report:

  • Better focus

  • Happier mood

  • Less anxiety

  • Better sleep

  • More emotional stability

  • More energy

These usually show up even before the HRV changes do.

The Big Takeaway

Contrast therapy is a simple, natural way to train your nervous system, boost HRV, and improve overall health. The key is:

Start slow. Stay consistent. Listen to your body.

Think of it like brushing your teeth—little bits often beat big efforts once in a while.

Caleb Fritz
Next

When to Use Ice vs. Heat (Made Super Simple)