Training guide
What is VO2 max?
VO2 max is the highest rate at which your body can take in and use oxygen during hard exercise. It is usually written in milliliters of oxygen per kilogram of body weight per minute. It sets an upper limit on endurance effort, but it is only one part of performance.
A lab test measures it from your breathing during a test that builds to exhaustion. A watch or ring only estimates it, usually from heart rate and pace or power on workouts.
What limits VO2 max
A review of the physiology concluded that in healthy people VO2 max is limited by how well the heart and lungs deliver oxygen to the working muscles. Three lines of evidence support this: changing oxygen delivery changes VO2 max, training raises it mainly through a higher maximal cardiac output, and a small muscle mass given extra blood flow can use oxygen at a very high rate.
The same review points out that VO2 max is not the whole story. Running economy and the fraction of VO2 max you can sustain also matter, and it names the speed at lactate threshold as the best single physiological predictor of distance running performance. Two athletes with the same VO2 max can perform very differently.
Lab number versus watch estimate
A watch cannot see your breathing gas. It estimates VO2 max from the relation between your heart rate and your speed or power across workouts, so the number depends on the quality of the heart rate data, a correct maximum heart rate and the type of workouts you do. It can change from week to week without any real change in fitness.
Treat the watch number as a trend from one source. Compare it with itself over weeks and months, and note which device produced it. Different brands use different methods and are not directly comparable.
What your AI can read in Memory.fit
Progress › Fitness shows VO2 max as the watch or app sends it: the latest value, the change over the period, a running and a cycling line when both exist, a usual range, and who estimated it. Memory.fit does not calculate VO2 max itself. Your AI reads the same series with get_daily_metrics and get_trends.
For threshold work, your AI can also read best efforts from get_best_efforts, such as your best 20 minute power or 5 km time, and thresholds saved in Training zones. Memory.fit reports numbers and gives no verdict on them.
In your AI
The AI you already use, with your data in Memory.fit.
- ChatGPTChatGPT plans your week, fuels your long sessions and writes it all back to Memory.fit.Set up ChatGPT
- ClaudeClaude writes your plans back to Memory.fit, and asks you before it replaces or removes something you have.Set up Claude
Grok BotGrok Bot plans and reviews from your real training, and can re-plan a week after a bad night's sleep.Set up Grok Bot
MuseMuse plans sessions from your real training and writes them into Memory.fit's Plan.Set up Muse
DotsOpenAI says a dot's background research uses your connected apps read only, so plans are written when you ask in the chat.Set up Dots- GeminiType @ in a Gemini chat and pick Memory.fit to ask about your training. Gemini asks you to allow each session it plans, and planning a whole week is not reliable yet.Set up Gemini
- GrokGrok reads your training, sleep and fuel, and can plan around them.Set up Grok
- Perplexity ComputerPerplexity Computer reads your training in Memory.fit. Whether it writes a plan back isn't checked yet.Set up Perplexity Computer
- Claude CodeClaude Code reads your training and writes the sessions it plans back to Memory.fit, asking before each change unless you allowed it.Set up Claude Code
CueYour Cue agents plan your week and write your fuel plans from your real training, sleep and recovery.Set up Cue
What to send
Copy one, send it to your AI.
“Show my VO2 max trend from my watch in Memory.fit over the last 6 months and tell me which device and sport it comes from.”
Tools:
get_daily_metricsget_trends“Set my VO2 max against my best efforts in Memory.fit over the same period. Do they move together?”
Tools:
get_best_effortsget_trends“Look at my training load and VO2 max together in Memory.fit and describe what changed over the last 12 weeks.”
Tools:
get_training_loadget_trends“Based on my data in Memory.fit, plan a 6 week block that includes interval sessions, and send them to my watch.”
Tools:
set_training_plansend_session_to_devices
Questions
In short.
It depends on age, sex, sport and measurement method, so no single number applies to everyone. Memory.fit shows your own trend and usual range rather than a score.
It is an estimate from heart rate and pace or power, not a measurement of breathing gas. It is most useful as a trend on one device.
Studies show training raises it, mainly through higher maximal cardiac output. How much depends on the person and the training. Your AI can help plan the training.
It sets an upper limit, but running economy and the fraction of VO2 max you can sustain matter too. Speed at lactate threshold was named the best single predictor of distance running performance.
No. It shows the VO2 max your watch or app sends, under that device's name.
Sources · Checked November 10, 2026
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