How to improve VO2 max for healthspan, longevity, and performance

Originally published on July 2, 2025

VO2 max is one of the clearest markers of aerobic fitness, healthy aging, and endurance performance, and it is more trainable than many people think. In Episode 330 of the WHOOP Podcast, Dr. Greg Grosicki joins Kristen Holmes, Global Head of Human Performance, Principal Scientist at WHOOP, to explain what VO2 max actually measures, why researchers use it to predict mortality and performance, and how people can improve it with the right mix of intervals, Zone 2 work, strength training, sleep, and recovery.

Grosicki is a WHOOP Senior Research Scientist and exercise physiologist who helped build the lab foundation behind the WHOOP VO2 max feature. His discussion grounds the metric in mechanism, published research, and training methods people can apply right away.

To listen to Episode 330 of the WHOOP Podcast in full, head to the WHOOP Podcast on YouTube.

What is VO2 max and why do exercise physiologists care about it

VO2 max is the highest rate at which your body can take in and use oxygen during exercise. It matters because it reflects how well the heart, lungs, blood, and working muscle coordinate to make energy and hold off fatigue.

Grosicki makes the case that the usual dictionary definition misses the reason the metric carries so much weight in exercise physiology. During exercise, oxygen has to be delivered to muscle, extracted from the blood, and used inside the muscle cell to generate ATP, the energy currency that powers movement. VO2 max captures that whole chain in one number, which is why it is useful for both racing and healthy aging.

Holmes also pushed the conversation beyond pure cardio. VO2 max reflects cardiorespiratory fitness, but it also tells you something about how well the musculoskeletal system can use the oxygen it receives. In practice, that means the number is connected to heart function, blood flow, mitochondrial function, and the ability of muscle tissue to keep doing work.

Grosicki summarized the metric this way:

"VO2 max is this integrated metric that reflects all of the bodily systems working together during physical activity or during work to produce energy and to prevent fatigue."

What you should take away

• VO2 max reflects the combined work of the heart, lungs, blood, and muscle during exercise.
• Higher VO2 max supports both better endurance performance and better resistance to fatigue.
• VO2 max is useful because it ties oxygen delivery and oxygen use into one measurement.

If you want to hear Grosicki unpack the physiology behind the Fick equation, listen to the full episode on Youtube.

How does WHOOP estimate VO2 max with lab-grade rigor

That definition only helps if the estimate is built on a strong reference standard. WHOOP built the VO2 max feature by training wearable data against gold-standard lab testing, rather than a loose field estimate.

Grosicki explained that the team followed guidance from the [InterLIVE consortium recommendations for wearable VO2 max validation]([LINK NEEDED]), published in Sports Medicine in 2022. Those recommendations spell out how wearable companies should validate physiological metrics, including the need for a clear target population and direct comparison against indirect calorimetry, the lab method that measures inhaled and exhaled gases to calculate oxygen consumption.

WHOOP brought more than 300 people into WHOOP Labs for testing. The sample was planned in advance to span age, sex, and fitness level, because a VO2 max estimate needs to work across the people who use it, not only in young trained athletes. Before testing, participants followed strict protocols around exercise, food, fluids, and medication use. During testing, WHOOP used a Parvo Medics metabolic cart and calibrated it before every session.

The team also checked whether each person had truly reached VO2 max. Grosicki described four key markers the lab reviewed, oxygen uptake plateau, rating of perceived exertion, respiratory exchange ratio, and peak heart rate. That matters because many validation efforts stop at a hard test, while a high-quality VO2 max dataset needs evidence that the maximal value was actually reached.

Grosicki described that process in specific terms:

"We brought in over 300 people to WHOOP Labs to do these tests. There were very strict protocols before they came in [...] and after every test [...] we looked at every single one of those metrics to validate that the training data [...] was absolutely gold standard."

For a broader look at how WHOOP measures physiology, see this earlier discussion of how WHOOP measures core training and recovery signals. Grosicki also revisits the research mindset behind wearable data in a later conversation about wearable use and health trends.

What you should take away

• WHOOP trained the VO2 max feature against more than 300 lab tests using indirect calorimetry.
• The validation sample was built to cover a wide age and fitness range, not a narrow athletic group.
• Each test was reviewed for true maximal effort using oxygen plateau, perceived exertion, respiratory exchange ratio, and peak heart rate.

If you want to hear Grosicki go deeper on how WHOOP built the validation dataset, listen to the full episode on Youtube.

Which physiological systems actually limit VO2 max

Once the estimate is trustworthy, the next question is what the number represents inside the body. Grosicki framed the answer through the Fick equation, which links VO2 max to cardiac output and the muscle's ability to extract oxygen from the blood.

In simple terms, cardiac output is how much blood the heart pumps each minute. It depends on heart rate and stroke volume, which is the amount of blood pumped with each beat. The second half of the equation is the arterial-venous oxygen difference, a measure of how much oxygen the working muscle pulls out of the blood that reaches it.

Grosicki argued that the main limiter of VO2 max is central, which means oxygen delivery is the bottleneck more often than oxygen extraction. He pointed to a classic [single-leg kicking experiment from Bengt Saltin and colleagues]([LINK NEEDED]) showing that muscle could use about 2 to 3 times more oxygen during isolated leg work than it did during whole-body maximal exercise. The muscle had unused capacity. Delivery from the cardiovascular system was the tighter constraint.

That is why stroke volume matters so much. At rest, a trained and an untrained person need a similar amount of oxygen. The trained person can meet that need with fewer beats because each beat pushes out more blood. Grosicki used that logic to explain why fitter people usually have lower resting heart rates. The same relationship scales up during hard exercise, where larger stroke volume supports much higher cardiac output.

As Grosicki put it when he broke down the equation:

"Every time the heart beats, how much blood is it pumping out? And that's gonna be the key driver of VO2 max and adaptation to VO2 max."

What you should take away

• The biggest physiological driver of VO2 max is usually oxygen delivery, especially stroke volume and total cardiac output.
• Lower resting heart rate in fitter people often reflects a heart that pumps more blood with each beat.
• Muscle extraction still matters, but the central delivery system is usually the main ceiling on VO2 max.

What VO2 max levels are linked to longevity and performance

VO2 max predicts both high performance and long-term survival. Grosicki called it one of the strongest single markers across the full spectrum, from elite sport to clinical risk.

On the longevity side, he highlighted classic and newer research. A large fitness and mortality study led by Steven Blair followed about 15,000 people for roughly a decade and found that higher fitness delayed mortality, largely through lower cardiovascular disease and cancer risk. Grosicki then pointed to the better known 2002 New England Journal of Medicine paper from Jonathan Myers and colleagues, which found that each 1 MET increase in exercise capacity, equal to 3.5 ml/kg/min of VO2 max, was associated with a 12% increase in survival.

He also cited a later [Myers-led cohort analysis of nearly one million people that broke participants into fitness quintiles. People in the highest fitness group were about 4.5 times less likely to die than people in the lowest fitness group. Grosicki noted that much of the protective range in these papers starts around 14 to 15 METs, which is roughly 45 to 50 ml/kg/min.

The most encouraging part of the evidence is where the biggest jump happens. Moving from the least fit group to the next group up produces a large share of the survival benefit. That means people do not need elite numbers to change their risk profile. Consistent training from a low baseline can have a major effect.

The number also changes with age. Grosicki said VO2 max usually begins to decline around age 25 to 30 and often falls about 10% per decade. He also noted data from John Holloszy and colleagues on active aging and aerobic capacity showing that sustained training can slow that decline to about 1 to 2% per decade.

Grosicki boiled the survival data down to one concrete figure:

"A 1 MET increase in your VO2 max [...] is associated with a 12% increase in survival."

What you should take away

• VO2 max is strongly linked to both endurance performance and lower mortality risk.
• A 1 MET increase in VO2 max, or 3.5 ml/kg/min, was linked to a 12% increase in survival in the Myers study.
• The largest health gain comes from moving out of the lowest fitness group, even before you reach high performance levels.
• Regular training can slow the age-related decline in VO2 max.

If you want to hear Grosicki go deeper on the studies behind VO2 max and mortality, listen to the full episode on Youtube.

How should you train to raise VO2 max

VO2 max improves when training targets the duration and intensity where the system is challenged most. Grosicki's practical answer was simple, if you want to improve your ability to sustain very hard efforts for 1 to 10 minutes, you need to train very hard efforts that live in that window.

He tied that idea to the SAID principle, specific adaptations to imposed demands. In other words, training should resemble the physiological demand you want to improve. For VO2 max, that means repeated efforts near maximal aerobic intensity, with enough recovery to preserve quality.

Grosicki listed several proven interval formats. One was 4 to 6 rounds of 5 minutes as hard as you can sustainably go, with 2.5 minutes of recovery. Another was 4 by 4 minutes with 4 minutes of recovery. Holmes added an important coaching point for people who are newer to the work. Start with shorter efforts if needed, even 1-minute intervals or power walking on a steep treadmill, then build toward longer sustained efforts as fitness improves.

He also cited a 2020 interval study from Brent Ronnestad and Carsten Lundby in Scandinavian Journal of Medicine & Science in Sports. Very fit cyclists, with an average VO2 max around 74 ml/kg/min, completed 3 rounds of 13 repetitions of 30 seconds hard and 15 seconds easy. After 3 weeks, VO2 max rose by about 5%. That is a strong result in athletes who were already highly trained.

Quality control matters as much as the workout design. Grosicki warned that the easy parts need to be very easy. If recovery between efforts stays too hard, later intervals drop below the target intensity and the session turns into moderate work rather than VO2 max work. Holmes added that a full warmup helps people reach the right heart rate and power sooner, which makes the early reps count.

Grosicki used the cyclist study to show what novelty and specificity can do:

"The cyclists they did this in had a VO2 max of 74 on average coming in. Three weeks of this boosted their VO2 max 5%."

WHOOP members who want a second practical read on interval structure can also use this guide on improving VO2 max.

What you should take away

• VO2 max work should usually target hard efforts that last about 1 to 10 minutes.
• Proven interval formats include 4 by 4 minutes, 4 to 6 by 5 minutes, and short hard intervals such as 30 seconds on and 15 seconds off.
• Easy recovery intervals need to stay easy enough to protect the quality of the next effort.
• One to two VO2 max sessions per week is usually enough.

If you want to hear Grosicki unpack interval structure and pacing errors, listen to the full episode on Youtube.

Where do Zone 2, strength training, and Recovery fit into a weekly plan

Those interval sessions work best when they sit inside a week that still includes easier aerobic work and lifting. Holmes framed the program around a familiar 80/20 split, with most aerobic time in Zone 2 and a smaller share in the higher intensity work that pushes VO2 max.

Grosicki's first rule was even simpler. Go from doing nothing to doing something, and make that something consistent. If all a person can sustain at first is walking, that still matters. If time allows, he recommended at least 150 minutes of aerobic activity per week, with one or two higher-intensity sessions layered on carefully.

Strength training is part of the plan, not a separate track. Grosicki said lifting twice per week supports performance and healthspan, and he pointed to research showing that adding strength work can improve 5-minute cycling power in already trained athletes. He also noted that resistance training helps preserve the force, tissue capacity, and movement economy people need as they age. For a deeper read on that side of the equation, see this WHOOP Locker piece on strength training programming for long-term performance.

Holmes also emphasized the foundation under the training itself. Sleep, fueling, hydration, and total life stress all affect whether a hard block creates adaptation. That is where WHOOP metrics become useful context. Recovery, HRV, resting heart rate, and Sleep can help show whether the body is absorbing the work or carrying too much fatigue. A red Recovery score does not automatically mean skip training, but it should prompt an honest review of sleep timing, nutrition, hydration, and recent load. WHOOP members who want more context on that decision can read this deep dive on how to interpret Recovery.

Grosicki gave a direct prescription on the role of lifting:

"Lift weights twice a week if you can. If you're not lifting weights twice a week, then you're not maximizing your gains."

What you should take away

• The best weekly VO2 max plan usually includes mostly easier aerobic work, one to two hard interval sessions, and two strength sessions.
• Going from no training to consistent training produces a large share of the health benefit tied to VO2 max.
• Recovery signals are useful context for deciding whether hard training is being absorbed well.
• Sleep, fueling, hydration, and life stress all affect how much VO2 max work your body can use productively.

The bottom line

• VO2 max reflects how well the body delivers and uses oxygen during exercise, which makes it a strong marker of both endurance capacity and healthy aging.
• WHOOP built the VO2 max feature against more than 300 indirect calorimetry tests collected under strict lab conditions.
• Stroke volume, the amount of blood pumped with each heartbeat, is a main driver of VO2 max and a key reason fitter people often have lower resting heart rates.
• A 1 MET increase in exercise capacity, equal to 3.5 ml/kg/min, was linked to a 12% increase in survival in the Myers study.
• The largest health gain comes from moving out of the lowest fitness group, which means even modest, consistent exercise can change long-term risk.
• VO2 max usually responds best to one to two weekly sessions of hard intervals that last about 1 to 10 minutes and preserve high-quality efforts.
• Zone 2 work and strength training belong in the same plan because they support aerobic development, tissue durability, and long-term function.
• Recovery, HRV, resting heart rate, and Sleep help show whether a VO2 max block is building fitness or stacking fatigue.

Frequently asked questions about things discussed in this episode

How does WHOOP estimate VO2 max?

WHOOP estimates VO2 max by training wearable data against gold-standard lab tests that measure oxygen use with indirect calorimetry. That lab foundation is what lets the app turn day-to-day physiological data into a VO2 max trend.

What does WHOOP track alongside VO2 max that helps you judge readiness?

WHOOP tracks Recovery, HRV, resting heart rate, Sleep, and Strain alongside VO2 max. Those signals help show whether hard aerobic work is being absorbed well or whether fatigue, poor sleep, or life stress is starting to limit adaptation.

How does WHOOP help with high-intensity interval training?

WHOOP helps with interval training by showing how hard sessions affect heart rate, Strain, and next-day Recovery. That context can make it easier to keep one or two hard sessions in the week without turning every session into medium effort.

What does WHOOP do if Recovery stays low during a VO2 max block?

WHOOP flags low Recovery as a sign to review sleep timing, nutrition, hydration, and total load before adding more intensity. A low score is a cue to adjust the full picture, not only the workout on the calendar.

How does WHOOP fit strength training into a VO2 max plan?

WHOOP fits strength training into a VO2 max plan by letting you see all training load in one place and relate it to Recovery. That matters when lifting supports movement economy and durability, but still adds fatigue that needs to be managed.

What does WHOOP show about fitness and sleep over time?

WHOOP shows that aerobic fitness and sleep often improve together over time. Holmes noted in the episode that fitter people tend to sleep more efficiently, which can support a better training and recovery cycle.

Tracking VO2 max, Recovery, resting heart rate, and Sleep together in the WHOOP app can show whether your weekly training mix is building a bigger aerobic engine or only creating more fatigue.