Cold Showers, Real Data: 90 Days Of HRV, Mood, And Sleep Changes

Why I Stopped Believing Cold Exposure Hype

I like stress tests. On code. On my body. On workflow.

Cold exposure sits in that weird space between bro science and actual physiology. You hear everything. Boosts testosterone. Cures depression. Doubles recovery. Makes you rich. Whatever.

I did not care about performance claims. I cared about numbers I already track obsessively: HRV, mood, and sleep depth.

So I ran a 90 day experiment. Daily cold showers, structured protocol, and boring consistent logging. No ice baths. No sauna contrasts. Just something that fits a normal life with kids and client projects.

This is what actually moved in my data. And what did not.

The Setup: Tools, Rules, And Baseline

I did not change my training, diet, or caffeine intake during this block on purpose. If I stack three variables I learn nothing.

Here is the exact stack I used.

• Wearable: Oura Ring Gen3, worn 24/7, at least 6 months baseline data.
• Tracking apps: Oura app for HRV and sleep, Apple Health bundle, and a simple custom Airtable base for mood and subjective notes.
• Training: 3x week strength (kettlebell + barbell), 2x week easy cardio, 8–10k steps per day. Nothing heroic.
• Sleep schedule: Target 23:00–07:00, with kids sabotaging that on a regular basis.

For 4 weeks before the experiment I did no deliberate cold exposure. Warm showers, normal life, same training. That gave me a baseline.

Baseline Numbers (4 Week Average)

• Nightly HRV (RMSSD): 62 ms average
• Resting heart rate: 51 bpm
• Deep sleep: 1h 23m average
• REM sleep: 1h 35m average
• Sleep efficiency: 89 %
• Mood rating (1–5, logged in morning): 3.3 average

Nothing crazy. Decent fitness. Some sleep interruption from kids. Classic mid 30s builder profile.

The Cold Shower Protocol

I wanted a protocol that a normal human can actually run for 90 days while working and coaching baseball, not a YouTube stunt.

This is what I settled on.

• Frequency: 1 cold shower every day. No rest days.
• Timing: Morning, within 45 minutes of waking, before coffee.
• Duration:
  Week 1: 30 seconds cold finish
  Week 2: 60 seconds cold finish
  Week 3–4: 2 minutes fully cold
  Week 5–13: 3 minutes fully cold
• Water temperature: Tap cold in the Netherlands. I measured 9–13 °C depending on the day.
• Breathing: Normal nasal breathing. No dramatic hyperventilation stuff.

All showers happened within a 2 hour window to keep timing consistent for circadian effects. I skipped cold exposure if I had a fever or clear signs of actual illness, which happened twice.

HRV: What Actually Happened

Most cold exposure content oversells HRV like you will magically turn into a monk by suffering under a shower head.

Reality was more boring and more interesting at the same time.

Immediate HRV Response

I did some spot checks with the Oura readiness graph and a separate HRV app (HRV4Training) pre and post shower during the first 2 weeks.

• During the shower: HR goes up, obviously. HRV drops. Sympathetic activation wins.
• 10–20 minutes after: Heart rate comes down, HRV rebounds slightly above pre shower values in about half the sessions.
• Subjective: I felt alert, but not jittery, once my skin warmed back up.

I stopped doing immediate session tests after week 2. The pattern was clear. Acute stress first, then a small rebound.

Nightly HRV Over 90 Days

The real question is if this stressor trained my system or just annoyed it.

Here are the nightly RMSSD averages by phase, compared to baseline 62 ms.

• Weeks 1–2: 59 ms average. Slight drop. I also felt more wiped on lifting days.
• Weeks 3–4: 61 ms average. Basically back to baseline.
• Weeks 5–8: 66 ms average. Small but consistent rise.
• Weeks 9–13: 67 ms average. Flat. No magical climb to 80+.

So across 90 days I saw roughly a 5 ms bump in average nightly HRV compared to the 4 week baseline, after a short adaptation dip.

Is that huge? No. Is it nothing? Also no.

If a supplement claimed a stable 5–8 % increase in HRV over 2–3 months with zero other changes, I would call that decent. Not a miracle. Just another small lever.

Mood: The Only Effect I Felt Immediately

Cold exposure people love the word "dopamine". You hear insane percentage increases tossed around like candy. None of those numbers help if your mornings still feel like mud.

I tracked mood very low tech. One rating every morning:

• 1 = awful
• 2 = low energy, grumpy
• 3 = neutral, functional
• 4 = good, motivated
• 5 = great, almost annoying to others

No fancy app. Just an Airtable form link pinned on my phone.

Baseline vs Cold Phase

• Baseline 4 weeks: 3.3 average
• Cold weeks 1–4: 3.6 average
• Cold weeks 5–13: 3.9 average

This was the most obvious change. Mood trended up and stayed up, and it tracked more with "did I do the cold shower" than with sleep duration.

On mornings when I skipped cold because I was sick, my rating dropped by roughly 0.5 on average, even if I had slept more hours.

Subjectively, the shift felt like this:

• The first 30 minutes of the day lost the gray filter.
• I procrastinated less on starting deep work blocks.
• I was less reactive with my kids before school.

I am not going to pretend cold showers cured anything. They did not. My stress on heavy project days still spiked. I still had bad nights of sleep and low energy evenings.

But that early morning "drag" softened a lot. That alone felt worth the inconvenience.

Sleep Depth: Small Shift, But Real

I care more about deep sleep than total hours. I can function well on 7 hours with 1h40 deep. I feel wrecked after 8 hours with 45 minutes deep.

The big risk with morning cold is that it might shift circadian signals. You slam your system with a stressor right after waking and no one really tells you what that does long term.

Timing And Routine

I kept the routine simple:

• Wake up.
• Toilet, weigh in, put coffee on.
• Cold shower for 2–3 minutes.
• 10 minutes light movement in the living room.
• Then first coffee.

So cold exposure always happened in the same slot, very early. No evening cold. No cold after 16:00.

Deep Sleep Numbers

• Baseline deep sleep: 1h 23m average
• Cold weeks 1–4: 1h 27m average
• Cold weeks 5–13: 1h 32m average

So I saw about a 9 minute increase in deep sleep, which is roughly a 10 % bump for me.

That is not life changing. It is also not noise. Over 90 days, the distribution shifted clearly upward. The number of nights with less than 60 minutes of deep sleep dropped from 23 % of nights to 11 %.

REM sleep did not really change. Maybe 2–3 minutes more on average, which I chalk up to random variance and kid wakeups.

Sleep Quality Subjectively

I care less about neat graphs and more about the "how hard is it to stand up" reality.

Patterns I noticed:

• On days with cold showers and normal training, I woke up less groggy even when total sleep dipped under 7 hours.
• On days with very heavy training (serious leg day or long baseball coaching), evening fatigue got sharper, but sleep felt denser. Shorter but deeper.
• If I did cold after a bad short night, I felt more functional by 09:00, but more tired by 20:00.

I did not see any sign that morning cold ruined my sleep. If anything, it made sleep quality more robust against bad days. That surprised me.

Recovery Perception vs Numbers

People talk about cold exposure for "recovery" like it is a magic reset button. I wanted to see if that matched reality when you lift and coach multiple times a week.

Muscle Soreness And Performance

I did not track soreness on a 1–10 scale, which I regret a bit. I did keep notes in my training log.

Pattern after week 3:

• DOMS intensity did not change much.
• DOMS duration shortened slightly, especially after heavy kettlebell swings and squats.
• Subjectively I was more willing to train while still mildly sore.

Cold showers in the morning did not make me feel instantly recovered. They made feeling slightly beat up more tolerable. There is a difference.

HRV As A Recovery Guide

I did not see cold exposure artificially inflate HRV so much that it masked real fatigue. That was one of my concerns.

On weeks where I overloaded training, HRV still dropped, even with daily cold showers. Cold did not hide that signal, it just sat on top as a background input.

This matters if you use HRV trends to modulate training load. Cold did not mess with that feedback loop in my case.

Things That Did Not Happen

What I did not see is probably more useful than the small wins.

• No giant spike in HRV into elite athlete territory.
• No magic fat loss.
• No sudden cure for stress or anxiety on heavy project weeks.
• No obvious boost in strength or cardio performance that I could tie directly to cold.

My lifts progressed the way they usually do on a decent program. Some weeks up, some down. Cold did not change that pattern.

Sleep still collapsed on nights when I stupidly checked email at midnight. No shower fixes that kind of poor decision.

What I Would Repeat, And What I Would Skip

After 90 days I had enough data to answer a simple question. Is this worth keeping in my life as a builder, coach, and dad with a finite patience budget?

What Stays

• 3 minute morning cold on work days, but not necessarily on weekends.
• Cold on high stress days where I know I will stare at a tough feature or architectural decision for hours. The mood lift matters there.
• Cold during deload weeks, not for muscle recovery, but for keeping the morning activation pattern stable while training volume is lower.

Mood and sleep depth were the two levers that sold me. HRV was a nice confirmatory signal, not the main reason.

What Goes

• Cold after late evenings. If I go to bed after midnight, I skip cold the next morning. The extra stress on already bad sleep feels counterproductive.
• Cold on days with borderline illness. Every time I tried that I felt worse by afternoon.
• Chasing longer durations. 3 minutes was enough. More just turned into a willpower contest.

How I Would Start If I Had To Do It Again

If you care about data instead of hero stories, I would keep it boring and measurable.

• Grab any half decent wearable that tracks HRV and sleep stages. Oura, Whoop, Apple Watch with apps, whatever.
• Collect 3–4 weeks of baseline with no deliberate cold. Log mood every morning with one single number.
• Run 8–12 weeks of daily cold showers in the morning, 1–3 minutes, fully cold. No extremes.
• Change nothing else if you can. Same training, foods, caffeine window.
• Ignore day to day swings. Look at 4 week averages, not magical single nights with perfect scores.

Then decide. Not from TikTok clips. From your own graphs.

For me, cold showers became a small, reliable lever. Not a personality. Not a lifestyle. Just another tool in the stack, next to kettlebells, blue light filters, and boring consistent sleep.

The experiment did not make me special. It made my mornings slightly better and my deep sleep slightly deeper. That is enough.