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Terra Research

Uncovering groundbreaking insights from the world's health data. Led by 2x Olympic champion Alistair Brownlee.

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All research papers

Here you can find all research papers on health data published by the Terra Research team. All papers consist of original findings.

VO2 Max

How Your Watch Actually Comes Up With Your Vo2 max

How Your Watch Actually Comes Up With Your Vo2 max

A sports watch turns power, pace and heart rate into a Vo2 Max through a chain of estimates. Here's each step, and where…

17 September 2026

Alistair Brownlee, Cameron Crawford +1

Sleep Tracking

An Evening Nap Pushes Your Bedtime Back 80 Mins

An Evening Nap Pushes Your Bedtime Back 80 Mins

We analyzed 340,889 nights that followed a nap. Before 11 AM a nap costs nothing, but after 5pm it moves bedtime by 80…

15 September 2026

Rocio Mexia Diaz, Kyriakos Eleftheriou

Women's Health

Pregnancy Shows Up in Wearable Data Before a Missed Period

Pregnancy Shows Up in Wearable Data Before a Missed Period

What 266 pregnancies reveal about how temperature, heart rate, and breathing change from the first days after…

8 September 2026

Rocio Mexia Diaz, Kyriakos Eleftheriou

Altitude Training

Your Body's Response to Altitude Is Highly Individual

Your Body's Response to Altitude Is Highly Individual

What 1,045 altitude nights reveal about why the same mountain hits people differently.

4 September 2026

Alistair Brownlee, Halvard Ramstad

Sleep Series

It Takes Four Days to Recover From a Night Shift

It Takes Four Days to Recover From a Night Shift

What 17,775 shift nights reveal about how night work changes sleep, REM, and recovery.

1 September 2026

Rocio Mexia Diaz, Kyriakos Eleftheriou

London Data

Food is Dirtier Than the Motor

Food is Dirtier Than the Motor

What 10 London commuting corridors reveal about the real carbon cost of bike, e-bike, Tube, and car commutes.

28 August 2026

Alistair Brownlee, Halvard Ramstad

Women's Health

Menopause Shows Up in Your HRV Before It Shows Up on the Calendar

Menopause Shows Up in Your HRV Before It Shows Up on the Calendar

What nightly HRV, sleep, and skin temperature reveal about perimenopause and menopause.

25 August 2026

Rocio Mexia Diaz, Kyriakos Eleftheriou

Altitude Training

Your HRV Recovers at Altitude Before Your Oxygen Does

Your HRV Recovers at Altitude Before Your Oxygen Does

What 50,572 altitude nights reveal about oxygen, heart rate, and recovery in thin air.

20 August 2026

Alistair Brownlee, Halvard Ramstad

Terra Smart Fill

Terra Smart Fill: Solving Missing Health Data

Terra Smart Fill: Solving Missing Health Data

How we use tabular machine learning research to fill in missing wearable data more accurately than your own average.

18 August 2026

Faraaz Akhtar, Kyriakos Eleftheriou

Norseman Power Data

How I came second in The World's Hardest Triathlon

How I came second in The World's Hardest Triathlon

What a two-time olympic triathlon champion's power and pace files reveal about how to pace the world's hardest…

4 August 2026

Alistair Brownlee, Halvard Ramstad

London Data

Cycling Is Good for You, But is it Faster Than Public Transport?

Cycling Is Good for You, But is it Faster Than Public Transport?

What 2,168 London morning bike commutes reveal about whether cycling beats the tube and the car.

31 July 2026

Alistair Brownlee, Halvard Ramstad

World Cup 2026

What Winning the World Cup Does to Your Health

What Winning the World Cup Does to Your Health

What the heart rates and step counts of thousands of Spaniards reveal about how a nation celebrated winning the World…

23 July 2026

Rocio Mexia Diaz, Kyriakos Eleftheriou

Heat Exposure

Running in 30°C Heat Barely Raises Your Heart Rate

Running in 30°C Heat Barely Raises Your Heart Rate

What 130,000 run activities reveal about how heat changes running.

21 July 2026

Alistair Brownlee, Halvard Ramstad

Heat Exposure

Heatwaves and Sleep

Heatwaves and Sleep

What 1.4 million nights reveal about the relationship between heat and sleep.

14 July 2026

Alistair Brownlee, Halvard Ramstad

World Cup 2026

The England vs Mexico Monday Morning Hangover

The England vs Mexico Monday Morning Hangover

What sleep data from 17,134 brits revealed about the night England beat Mexico.

7 July 2026

Alistair Brownlee, Halvard Ramstad

Research Publication

Terra Research Published in Nature Portfolio

Terra Research Published in Nature Portfolio

What 185,143 nights of wearable data reveal about sleep and daylight, now in npj Biological Timing and Sleep.

26 June 2026

Faraaz Akhtar, Cameron Crawford +2

Heat Exposure

Stacking Sauna and Cold Plunge, or?

Stacking Sauna and Cold Plunge, or?

We analyzed ~31,000 days of sauna and cold plunge use to examine whether combining them beats doing either one alone.

23 June 2026

Kyriakos Eleftheriou, Halvard Ramstad

Heat Exposure

Does Heat Make You Slow Down, or Tell You to Slow Down?

Does Heat Make You Slow Down, or Tell You to Slow Down?

What ~3,500 tracked run sessions reveal about how heat changes the way we run.

18 June 2026

Alistair Brownlee, Halvard Ramstad

World Cup 2026

The World Cup Hosts Don't Play Much Football

The World Cup Hosts Don't Play Much Football

What 30,000+ tracked football sessions reveal about the way different countries train, compete, and play.

16 June 2026

Rocio Mexia Diaz, Kyriakos Eleftheriou

Sleep Series

Late Dinners Raise Your Heart Rate When You Sleep

Late Dinners Raise Your Heart Rate When You Sleep

Our data from ~500 nights shows eating late raises your sleeping heart rate by 1.54 bpm, and the effect lasts the entire…

11 June 2026

Rocio Mexia Diaz, Alistair Brownlee

Heat Exposure

Does Hot Weather Change How Londoners Exercise?

Does Hot Weather Change How Londoners Exercise?

We analyzed 20,000 outdoor sessions across May to see how heat exposure change our exercise habits.

4 June 2026

Alistair Brownlee, Halvard Ramstad

Bed Sharing

Do People Sleep Better Alone or Together?

Do People Sleep Better Alone or Together?

Does sharing a bed actually help you sleep better? We analyzed n=25,086 nights to find out.

28 May 2026

Alistair Brownlee, Halvard Ramstad

Parkrun vs VO2 Max

Is Parkrun a Better Measure of Fitness Than VO2 Max

Is Parkrun a Better Measure of Fitness Than VO2 Max

What does your everyday training data really reveal about your fitness? We analyzed 1,613 park runs to find out.

21 May 2026

Alistair Brownlee, Halvard Ramstad

Sleep Series

Your Evening Workout Is Costing You Sleep

Your Evening Workout Is Costing You Sleep

Does the timing of your workout actually affect your sleep? We ran the data to find the window that delivers the most…

19 May 2026

Faraaz Akhtar, Kyriakos Eleftheriou

Cycling

Does Watching Sports Inspire Us to Exercise?

Does Watching Sports Inspire Us to Exercise?

Does watching professional cycling actually inspire us to ride? We analyzed ~265,000 outdoor cycling activities to test…

14 May 2026

Alistair Brownlee, Halvard Ramstad

Dreaming

What Actually Makes Us Dream?

What Actually Makes Us Dream?

Why do we remember some dreams and not others? We analyzed over 130,000 nights of sleep to find out what kind of nights,…

12 May 2026

Rocio Mexia Diaz, Kyriakos Eleftheriou

Running

Data Shows Most Runners Don't Actually Get Faster

Data Shows Most Runners Don't Actually Get Faster

How do runners actually get faster? We analyzed 856,000 running activities to find out who actually gets faster. It…

7 May 2026

Alistair Brownlee, Halvard Ramstad

Marathon Series

The Data Behind the London Marathon

The Data Behind the London Marathon

While Sabastian Sawe was busy breaking the two-hour marathon barrier in London, the watches of 571 amateur runners told…

27 April 2026

Alistair Brownlee, Cameron Crawford +1

London Data

Tube Strikes Made Londoners Active

Tube Strikes Made Londoners Active

During the April 2026 Tube strikes, Londoners adapted by cycling more—activity tripled, e-bike commutes rose 13%, and…

24 April 2026

Rocio Mexia Diaz, Kyriakos Eleftheriou

Endurance Training

Running Is The Hardest Endurance Sport? Not so Fast

Running Is The Hardest Endurance Sport? Not so Fast

Which sport is hardest on the heart? We ran the question through hundreds of thousands of sessions across nine activity…

23 April 2026

Alistair Brownlee, Halvard Ramstad

Heat Exposure

Cold Plunging Might Make Your Biomarkers Worse

Cold plunge chart

We analyzed large-scale wearable data to understand what cold exposure actually does to your body. Sporadic plunges act…

14 April 2026

Rocio Mexia Diaz, Kyriakos Eleftheriou

Winter Training

How The Fittest Do Winter

How The Fittest Do Winter

We analyzed 856,000 exercise sessions from Europeans across 20 countries to find out how people really train across the…

9 April 2026

Alistair Brownlee, Halvard Ramstad

Period Tracking

Your Breathing Changes a Week Before Your Period

Your Breathing Changes a Week Before Your Period

We often hear that our hormones make us unpredictable, but the data tells us otherwise: its a subtle but shockingly…

7 April 2026

Rocio Mexia Diaz, Alistair Brownlee

Alcohol Effects

Alcohol Doesn't Ruin Your Sleep The Way You Think

Alcohol Doesn't Ruin Your Sleep The Way You Think

We analyzed 15,000 nights of sleep data to uncover what drinking before bed actually does to your rest. Using a mixed…

30 March 2026

Faraaz Akhtar, Alistair Brownlee

Sauna

Saunas Lower Your Heart Rate More Than Exercise

Saunas Lower Your Heart Rate More Than Exercise

We analyzed 59,000+ daily records from 256 sauna users to quantify what saunas actually do to your body. Using paired…

26 March 2026

Rocio Mexia Diaz, Kyriakos Eleftheriou

Peptides

What GLP-1s are Really Doing to Your Training

What GLP-1s are Really Doing to Your Training

We analysed over 70,000 activities from 305 GLP-1 users to understand how these medications alter physiological…

23 March 2026

Rocio Mexia Diaz, Alistair Brownlee

Supplement Tracking

Caffeine Kills Your Deepest Sleep First

Caffeine Kills Your Deepest Sleep First

We analyzed 37,000+ nights of wearable data to understand how caffeine really affects your sleep. The results? Caffeine…

17 March 2026

Alistair Brownlee, Faraaz Akhtar +1

Peptides

GLP-1s: The Real Tradeoffs Nobody Tells You About

GLP-1s: The Real Tradeoffs Nobody Tells You About

We studied 500+ users. Notable side effects are activity drops, resting heart rate rises, and HRV drops well below…

12 March 2026

Rocio Mexia Diaz, Halvard Ramstad +1

Supplement Tracking

Melatonin’s Real Effect Peaks on Day 4 - And It's NOT Sleep

Melatonin’s Real Effect Peaks on Day 4 - And It's NOT Sleep

Most people take melatonin expecting to fall asleep faster or sleep longer. We analyzed over 200,000 sleep records from…

5 March 2026

Rocio Mexia Diaz, Alistair Brownlee +1

Cycle Tracking

Can We Predict Cycle Phase Without Temperature?

Can We Predict Cycle Phase Without Temperature?

Temperature has long been the go-to for tracking the menstrual cycle with wearables, but it turns out your body offers…

27 February 2026

Alistair Brownlee, Rocio Mexia Diaz +1

Winter Olympics

The Secret Behind Norway's Olympic Dominance

The Secret Behind Norway's Olympic Dominance

Norway claimed 41 medals at the 2026 Milano-Cortina Winter Olympics, more than any nation in a single Winter Olympic…

23 February 2026

Alistair Brownlee, Halvard Ramstad

Marathon Training

Simulate Your Next Marathon Race Pace

Simulate Your Next Marathon Race Pace

This week's research blog dives into a data-driven model that unlocks marathon potential by explaining 79% of finish…

20 February 2026

Alistair Brownlee, Halvard Ramstad

Marathon Training

How To Train For Your Next Marathon

How To Train For Your Next Marathon

Instead of treating training like a simple “more in = faster out” equation, we tested where the curve bends using six…

12 February 2026

Alistair Brownlee, Halvard Ramstad

Academic Research

Seasonal Effects on Sleep Performance

Seasonal Effects on Sleep Performance

We used a large anonymized dataset to track nights of sleep from people across hundreds of countries to understand how…

11 February 2026

Alistair Brownlee, Cameron Crawford +2

Marathon Training

The Easier You Train The Faster You Finish

The Easier You Train The Faster You Finish

We analyzed training data from 425 verified marathon runners to figure out what actually makes people faster. The…

5 February 2026

Alistair Brownlee, Halvard Ramstad

Women's Health

How Temperature Predicts Women's Cycle Phases

How Temperature Predicts Women's Cycle Phases

We analyzed ~3 million nights of wearable sleep data to see whether the menstrual cycle leaves a measurable signature in…

29 January 2026

Alistair Brownlee, Rocio Mexia Diaz +1

Sleep Tracking

Sleep Metric Variation Across Wearables

Sleep Metric Variation Across Wearables

We analyzed sleep data from 77,000+ nights across six major wearables, then zoomed in on same-person, same-night…

22 January 2026

Alistair Brownlee, Faraaz Akhtar +1

New Year Resolutions Cliff

The January Activity Spike: A two-day Story

The January Activity Spike: A two-day Story

We analysed wearable data from over 3,000 users to measure the New Year's resolution effect on physical activity. The…

15 January 2026

Alistair Brownlee, Faraaz Akhtar +1

Sleep Tracking

Sleep Patterns Across the World

Sleep Patterns Across the World

We analyzed 8,298 sleep records from October 2025 across wearable users in North America, Europe, and beyond, linking…

6 January 2026

Alistair Brownlee, Faraaz Akhtar +1

New Year Resolutions Cliff

New Year’s Resolutions Cliff

New Year’s Resolutions Cliff

Every January, millions pledge to sleep more along with their New Year's Resolutions. But does it work? Analyzing more…

31 December 2025

Alistair Brownlee, Cameron Crawford

Sleep Tracking

How HRV Actually Works

How HRV Actually Works

We unpack what HRV really is and how it actually works to demystify the data from Apple Watch, Fitbit, and Garmin. Some…

17 December 2025

Alistair Brownlee, Cameron Crawford +1

Sleep Tracking

How Do People Really Use Wearables?

How Do People Really Use Wearables?

We analyzed 93 days of continuous sleep data across Fitbit, Apple Watch, and Garmin users to answer a simple question:…

9 December 2025

Alistair Brownlee, Cameron Crawford

Sleep Tracking

Benchmarking Wearable Sleep Data Reliability

Benchmarking Wearable Sleep Data Reliability

We analyzed sleep data from over 5,000 real-world nights across Apple Watch, Fitbit, and Garmin users. Garmin delivered…

28 November 2025

Halvard Ramstad, Alistair Brownlee +1

Sleep Tracking Series

Is Consistency Actually More Important Than Intensity?

Is Consistency Actually More Important Than Intensity?

In this report, we reveal why high-step users averaging 11,500+ daily steps succeed: consistency. Their 36% activity…

23 October 2025

Alistair Brownlee, Cameron Crawford

Sleep Tracking Series

Which activity metrics actually matter? 28,000+ days analysed

Which activity metrics actually matter? 28,000+ days analysed

Smart rings track five different activity metrics, but they don't always align. Drawing on nearly 28,000 days of user…

9 October 2025

Alistair Brownlee, Cameron Crawford

Sleep Tracking Series

Burn More Calories, Sleep Like a Log?

Burn More Calories, Sleep Like a Log?

An analysis of 1,000+ ring users examined the relationship between daily calorie expenditure and sleep metrics. Active…

2 October 2025

Alistair Brownlee, Cameron Crawford

Sleep Tracking Series

GAMM analysis – can complexity tell us anything we don’t already know?

GAMM analysis – can complexity tell us anything we don’t already know?

Based on an analysis of nearly 90,000 nights, the connection between sleep duration and next-morning HRV is minimal for…

25 September 2025

Alistair Brownlee, Cameron Crawford

Sleep Tracking Series

Think a good HRV score follows a good night’s sleep? Think again!

Think a good HRV score follows a good night’s sleep? Think again!

Despite their perceived link, sleep and HRV are only weakly correlated. The analysis of nearly 90,000 nights showed that…

20 September 2025

Alistair Brownlee, Cameron Crawford

Sleep Tracking Series

Descriptive HRV using Z scores

Descriptive HRV using Z scores

Based on an analysis of nearly 100,000 HRV records, this report reveals that most daily HRV changes are small, but…

19 September 2025

Alistair Brownlee, Cameron Crawford

Sleep Tracking Series

Why Mondays Might Be Your Healthiest Day: What 1,000+ Sleepers Taught Us About Recovery

Why Mondays Might Be Your Healthiest Day: What 1,000+ Sleepers Taught Us About Recovery

At Terra, we recently ran an analysis on wearable data from over a thousand users, focusing on two key metrics: sleep…

18 September 2025

Alistair Brownlee, Cameron Crawford

Meet the Research Team

A team of scientists, engineers, and athletes working to make sense of the world’s health data.

Alistair Brownlee

Alistair Brownlee

Head of Research

Alistair Brownlee is Head of Research, where he leads large-scale analysis of wearable health data to better understand sleep, recovery and human performance, translating these insights into products that help people live healthier lives.

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Faraaz Akhtar

Faraaz Akhtar

AI and Health Researcher

Faraaz Akhtar is an AI & Health Researcher at Terra API, where he develops statistical and machine-learning methods to extract insights from large-scale wearable health data.

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Rocio Mexia Diaz

Rocio Mexia Diaz

AI and Health Researcher

Rocio Mexia is a Biomedical Engineer and AI & Health Researcher at Terra API, where she applies machine learning to wearable and health record data to uncover insights about human health.

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Halvard Ramstad

Halvard Ramstad

Editor-in-Chief

Halvard Ramstad is Editor-in-Chief at Terra Research, responsible for shaping how the team's findings reach the world.

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Cameron Crawford

Cameron Crawford

AI Engineer

Cameron Crawford is an AI Engineer at Terra API, solving the technical and product issues that arise when giving AI access to health data.

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Kyriakos Eleftheriou

Kyriakos Eleftheriou

CEO

Kyriakos Eleftheriou is the Founder and CEO of Terra API.

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