3 zone vs 5 zone training: heart rate, power and pace
3-zone vs 5-zone training models, heart rate vs power vs pace zones, and why cardiac drift makes your heart rate climb on easy runs at the same pace.
The fitness number linked to a longer life →Your VO2max,
Your VO2max,
from every watch.
See your VO2max over time, your fitness tier for your age and sex, and what actually moves it — training, sleep and recovery. All in one place.
✓ Launching soon — Garmin first✓ Free✓ No ads, no data sale✓ Delete everything in one click
VO2max · ml/kg/min
62
JulAugSepOct
48Resting HR
71HRV ms
+3.112-week Δ
Example data · Data source: your watch
lower risk of death for each 1-MET (3.5 ml/kg/min) of extra fitness
Kodama et al., JAMA 2009 →
~0×higher adjusted mortality in the least fit group than in elite performers
Mandsager et al., JAMA Netw Open 2018 →
+0%VO2max in 8 weeks with 4×4 intervals, where steady running didn't move it
Helgerud et al., MSSE 2007 →
How it works
One number that sums up your engine
VO2max is the most widely used measure of aerobic fitness. We bring it together from your devices and show you how to move it.
Every watch
Garmin first, with Polar, COROS, Suunto, Fitbit, Oura, WHOOP and Strava on the roadmap.
Your tier
Eight tiers from Iron to Mythic, based on age- and sex-adjusted fitness norms. See where the next one starts.
Ask your data
Connect Claude through MCP and ask “why was my last interval session hard?” — with your own numbers.
Irontier 1
Bronzetier 2
Silvertier 3
Goldtier 4
Platinumtier 5
Diamondtier 6
Elitetier 7
Mythictier 8
Free tools
Know your number
Estimate your VO2max and fitness age in a minute, compare with your age group, and see what it means in your sport.
Research library
49 landmark studies, one line each.
From the 1967 athlete tests to today's wearable validation studies: what each one found about fitness, health and training.
Explore the researchFrom the blog
VO2max, research, health and sport
Free, evidence-based articles, with sources at the end of every one.
Trending
7,000 vs 10,000 steps a day: what the research says
Is 10,000 steps a day necessary? Large meta-analyses link about 7,000 steps to much lower risk of death. What that means and how steps relate to VO2max.
Apple Watch VO2max: accuracy, levels and how to raise it
Apple Watch shows your VO2max as Cardio Fitness. Where to find it, what the four levels mean, how accurate it is and why it can read low.
Your data, your rules
We only read what you allow, never sell data, never use it for ads, and delete it when you disconnect. Read the privacy policy and the data use policy.