VO₂ Max Explained: What It Means and How Your Wearable Estimates Your Fitness

Many modern wearable devices display a VO₂ max estimate, often describing it as your cardiovascular fitness or aerobic capacity. It is one of the most recognised measurements in exercise physiology and is frequently used by athletes, coaches and healthcare professionals to assess endurance performance.

Despite this prominence, VO₂ max is often misunderstood. A high score does not automatically make someone a better athlete, and a lower score does not necessarily indicate poor health. Like most wearable metrics, VO₂ max is most valuable when read alongside other measurements such as heart rate, recovery, sleep and training load — not as a verdict on its own.

VO₂ max stands for maximal oxygen consumption. It represents the maximum amount of oxygen your body can use during intense exercise. The more oxygen your muscles can utilise, the more energy they can produce through aerobic metabolism.

VO₂ max is usually expressed as millilitres of oxygen per kilogram of body weight per minute (mL/kg/min). Higher values generally indicate a greater capacity for sustained aerobic exercise, which is why it has long been used as a benchmark in endurance sports.

VO₂ max is considered one of the strongest indicators of aerobic fitness. It reflects how effectively your heart pumps blood, your lungs absorb oxygen, your blood transports that oxygen, and your muscles use it during exercise.

Higher aerobic capacity often allows people to exercise for longer, recover more efficiently, perform endurance activities with less fatigue, and sustain faster running or cycling speeds. It is also associated with long-term cardiovascular health and physical function — making it relevant not just for athletes but for anyone who exercises regularly.

However, VO₂ max is only one part of overall athletic performance and health.

Most smartwatches do not directly measure oxygen consumption. Instead, they estimate VO₂ max using algorithms that analyse your heart rate response relative to your exercise intensity, alongside personal factors:

• Heart rate during exercise
• Running or walking speed / GPS pace
• Exercise duration and elevation changes
• Personal characteristics such as age and sex

The algorithm compares how hard your heart is working at a given pace to estimate aerobic capacity. Different manufacturers use different methods, so VO₂ max values may vary between devices and should not be compared across brands.

The most accurate measurement is a laboratory test where you exercise on a treadmill or cycle ergometer while wearing a mask that measures oxygen and carbon dioxide exchange. Wearable estimates are useful for tracking personal trends — but they are not equivalent to lab testing.

Several factors influence your VO₂ max score:

• Regular aerobic training — consistent endurance exercise (running, cycling, swimming, rowing, brisk walking) is the most effective way to improve VO₂ max; improvement typically occurs over weeks and months, not days
• Age — VO₂ max naturally declines with age; remaining physically active can slow this decline and help preserve cardiovascular fitness into later decades
• Genetics — some individuals have naturally higher VO₂ max values despite similar training, which is one reason why comparing your score with others is rarely useful
• Body composition — because VO₂ max is expressed relative to body weight, changes in body composition can affect the reported value even if your underlying aerobic capacity remains similar
• Illness, fatigue and dehydration — poor sleep, illness or heavy training can temporarily affect the accuracy of wearable estimates; a single low reading should not be a cause for concern

Yes — most recreational athletes can improve aerobic capacity through structured training. Evidence-based strategies include:

• Regular aerobic exercise, prioritising consistency over intensity
• Zone 2 endurance sessions — steady, conversational-pace efforts that build the aerobic base
• High-intensity interval training (HIIT) — used sparingly alongside lower-intensity work
• Gradual increases in weekly training volume (the 10% rule as a rough guide)
• Adequate recovery between sessions; see Recovery Score Explained
• 7–9 hours of quality sleep per night
• Balanced nutrition to support training adaptation

The rate of improvement varies considerably between individuals and depends on training history, genetics and overall health.

Not necessarily. Two runners may have identical VO₂ max values yet perform very differently in races. Performance also depends on running economy, lactate threshold, muscular strength, technique, nutrition, recovery strategy and mental resilience.

VO₂ max describes the size of your aerobic engine — but not how efficiently you use it. An athlete with a lower VO₂ max who uses their capacity more efficiently (better running economy, higher lactate threshold) can often outperform a higher-scored peer. Tracking your heart rate zones during training helps you understand how efficiently your aerobic system operates at various intensities.

VO₂ max becomes much more useful when interpreted alongside other measurements rather than in isolation:

• Heart Rate Variability (HRV) — reflects how your nervous system is adapting to training stress
• Resting heart rate — a complementary marker of cardiovascular fitness and recovery
• Heart Rate Recovery — how quickly your heart returns to baseline after exercise
• Recovery Score — your body's day-to-day readiness for training
• Sleep quality and duration
• Training load and session intensity

Looking at these measurements together provides a far more complete picture of fitness and health than relying on VO₂ max alone.

VO₂ max is only one piece of your overall health picture. Healio360 combines VO₂ max trends with HRV, heart rate recovery, resting heart rate, recovery score, sleep quality, daily activity, blood test results, medical reports, and AI-generated health insights — all analysed together over time.

Your Health Intelligence panel surfaces how cardiovascular fitness interacts with your recovery, sleep and overall wellbeing automatically, so you see the connections without having to switch between separate apps or manual spreadsheets.

A lower VO₂ max estimate is not a medical diagnosis and should not cause alarm on its own. However, seek medical assessment if reduced exercise capacity is accompanied by:

• Chest pain or tightness
• Severe shortness of breath disproportionate to exertion
• Fainting or near-fainting
• Persistent dizziness
• Palpitations during or after exercise
• A sudden unexplained decline in exercise tolerance

Wearable devices support health monitoring but should not replace professional medical assessment when concerning symptoms occur. You can check your symptoms to help structure what to discuss with your GP.

This guide is for educational purposes only and does not constitute medical or clinical advice. Always consult a qualified healthcare professional if you have concerns about your health.