If you wear an Apple Watch or another fitness tracker, you may have noticed a metric called VO₂max.
Most people see the number but don’t know what it means. Others assume it only matters for endurance athletes.
In reality, VO₂max is one of the most important indicators of overall health and long-term fitness.
VO₂max refers to the maximum amount of oxygen your body can use during exercise. Simply put, it measures how well your heart, lungs, and muscles work together to produce energy.
The higher your VO₂max, the greater your body’s ability to deliver oxygen to working muscles and use that oxygen efficiently.
Why VO₂max Matters
Researchers have consistently found that higher cardiorespiratory fitness is linked to lower risk of heart disease, metabolic disease, and early death. In fact, low aerobic fitness has been shown to carry risks similar to well-known factors like smoking or diabetes.
But beyond research, VO₂max also affects everyday life.
Think of it as your physical ceiling. Daily activities such as climbing stairs, carrying groceries, or walking uphill require a certain amount of energy. When your VO₂max is low, those activities take up a larger percentage of your capacity.
When your VO₂max is higher, the same tasks feel easier.
Unfortunately, aerobic fitness tends to decline with age, especially for people who are mostly sedentary. The encouraging news is that it can improve at almost any age with the right training.
How VO₂max Improves
Improving VO₂max requires changes in both the heart and the muscles.
Your heart becomes stronger and pumps more blood with each beat. At the same time, your muscles develop more mitochondria, the structures that help convert oxygen into usable energy.
Two types of training help drive these changes: steady aerobic exercise and higher-intensity intervals.
This is where Zone 2 training plays an important role.
The Importance of Zone 2 Training
Zone 2 training usually falls around 60–70% of your maximum heart rate. It should feel steady and manageable. You can still carry on a conversation, but you are clearly exercising.
Even though it doesn’t feel extremely hard, Zone 2 produces important adaptations in the body. It helps increase mitochondrial density, improve fat metabolism, and build the small blood vessels that deliver oxygen to muscles.
In simple terms, Zone 2 builds the foundation of your aerobic system.
Without that foundation, high-intensity training can feel overly stressful and less effective. Many people spend too much time exercising in a moderate “middle zone” that is too hard to recover from but not hard enough to significantly improve fitness.
Regular Zone 2 work helps build endurance while supporting recovery and overall cardiovascular health.
Zone 2 Doesn’t Have to Mean Long Cardio Sessions
One question that often comes up when people hear about Zone 2 training is whether it means spending 30–45 minutes continuously on a treadmill, bike, or rower.
That is certainly one way to do it, but it is not the only way.
Zone 2 is defined by your heart rate and effort level, not by the specific activity. As long as your heart rate stays in that moderate range — where you can still talk in full sentences but are clearly working — you are training your aerobic system.
For many people, this can happen during circuit-style workouts as well.
Moving through a steady rotation of exercises such as sled pushes, kettlebell carries, bodyweight movements, light resistance work, or moderate rowing can keep the heart rate elevated without pushing into very high intensity. When transitions are smooth and rest periods are short, the body can remain in a Zone 2 effort for much of the session.
This type of training can build aerobic capacity while also developing strength, coordination, and movement skill.
In other words, Zone 2 training is not limited to traditional cardio machines. It can emerge from many different training styles as long as the intensity remains controlled and sustainable.
For many people, this approach makes aerobic training more engaging and easier to maintain over time.
The Often Overlooked Role of Strength Training
While aerobic exercise is essential for improving VO₂max, strength training also plays an important supporting role.
As we age, we naturally lose muscle mass. This process, known as sarcopenia, can reduce strength, mobility, and metabolic health. When muscle mass declines, the body becomes less efficient at using oxygen and producing energy.
Resistance training helps counteract this process by maintaining and building lean muscle tissue.
Stronger muscles allow the body to perform work more efficiently. They also support joint health, improve insulin sensitivity, and help maintain metabolic function. Together, these changes support overall fitness and make aerobic training more effective.
Cardiovascular training and strength training are not competing priorities. They work together to support long-term health and performance.
VO₂max as a Measure of Capacity
Another way to think about VO₂max is as a measure of capacity.
When your aerobic capacity is low, everyday stressors take up more of your available energy. Physical activity, poor sleep, or emotional stress can feel harder to manage.
A higher VO₂max gives you more margin. Your body can handle daily demands with less strain, and recovery tends to improve.
For this reason, improving aerobic fitness is not just about exercise performance. It is about building resilience.
What This Looks Like in Practice
For most adults, a balanced approach to training works best:
- Perform Zone 2 aerobic exercise 3–4 times per week for about 30–45 minutes.
- Include 1–2 sessions of higher-intensity intervals each week.
- Strength train 2–3 times per week to maintain muscle and metabolic health.
- Prioritize sleep and recovery.
Wearable devices can provide useful feedback, but the exact VO₂max number is less important than the trend over time.
Small, consistent improvements add up.
Final Thoughts
VO₂max is not just a number on a fitness watch. It is a reflection of how well your body produces and uses energy.
Improving it does not require extreme training. In fact, much of the progress comes from consistent, moderate aerobic work combined with regular strength training.
Over time, this combination builds a stronger heart, healthier muscles, and a greater capacity to handle the physical demands of everyday life.
And that capacity is one of the most powerful investments you can make in long-term health.