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Quick answer. VO₂ max is the maximum amount of oxygen your body can use during exercise, measured in ml/kg/min. It's the single best proxy for cardiovascular fitness and one of the strongest predictors of lifespan we have. Men in the top 5% of VO₂ max live around 5 years longer than those in the bottom 5%. You can check your VO₂ max on an Apple Watch, Garmin or Whoop, and improve it with HIIT, tempo runs, zone-2 cardio and — with clinical evidence — KSM-66® ashwagandha, which has been shown to raise VO₂ max by +13.6% in 12 weeks. Ashwagandha is a core ingredient in Himmense BOOST.
In this guide
- What is VO₂ max?
- How is VO₂ max measured?
- Why is VO₂ max important?
- VO₂ max & lifespan
- How to improve your VO₂ max
- Ashwagandha, BOOST and VO₂ max
What's your fitness age?
How old is your body — in other words, what's your fitness age vs your actual age?
Unlike your actual age, your fitness age is largely determined by your VO₂ max: a measurement of how well your body uses oxygen. If your VO₂ max is high, you have a strong capacity for aerobic endurance — which means you might be much younger than your driver's licence says, and likely to live longer. A low VO₂ max is associated with increased risk of dying from cardiovascular disease, and to a lesser extent from cancer.
You can measure your VO₂ max with a smartphone or smartwatch — and the good news is that, unlike your actual age, you can lower your fitness age with the right kinds of activity.
What is VO₂ max?
VO₂ max (also known as maximal oxygen uptake or simply VO₂) is a measure of the maximum amount of oxygen a person can consume during exercise. It's typically measured in millilitres of oxygen per kilogram of body weight per minute (ml/kg/min). It's widely accepted as the best indicator of cardiovascular fitness and endurance capacity — and is used by sports scientists, coaches and athletes to monitor training, evaluate performance and predict success in endurance events.
A high VO₂ max is associated with better endurance and overall fitness, and is generally considered a sign of good health. Other factors such as muscle fibre type, lactate threshold and running economy also play a role in endurance performance, but VO₂ max is the headline number.
How is VO₂ max measured?
VO₂ max is usually measured in millilitres of oxygen per kilogram of body weight per minute (ml/kg/min). You can view your VO₂ max on your smartwatch. For example, on an Apple Watch:
- Open the Health app on your iPhone, then tap Browse.
- Tap Heart, then tap Cardio Fitness.
- Tap D, W or Y to view your average for the Day, Week or Year.
- Tap Show All Cardio Fitness Levels.
- Tap a cardio fitness level to compare your results against age and sex norms.
If your VO₂ max is below average for your age group, your fitness age is older than your actual age — and vice versa. A 30-year-old can have a fitness age anywhere between 20 and 79, depending on VO₂ max.
Why is VO₂ max important?
VO₂ max is important because it measures your body's ability to transport and use oxygen during physical activity. Oxygen is essential for energy production — the more oxygen you can consume, the more energy you can produce. A higher VO₂ max leads to better cardiovascular fitness and endurance capacity, which translates to improved performance in running, cycling, swimming and any endurance sport.
VO₂ max is also a marker of overall health. A low VO₂ max is associated with increased risk of chronic disease including heart disease, type 2 diabetes and obesity. Regular exercise is one of the most effective ways to improve VO₂ max — and a higher VO₂ max is generally considered a sign of good health.
Survival of the fittest: VO₂ max & lifespan
Cardiovascular fitness has a shocking impact on your chances of dying — particularly from cardiovascular disease, and to a lesser extent from cancer. Research shows even a minimal improvement in your fitness level significantly lowers your risk.
In a study published in the Journal of the American College of Cardiology, researchers looked at cardiorespiratory fitness (CRF) in over 5,000 men (average age 49 at baseline) with a single VO₂ max measurement, and compared that against mortality nearly five decades later. Participants in the highest 5% of VO₂ max lived about 5 years longer than those in the bottom 5%.
In another study in JAMA Oncology, individuals with low VO₂ max were shown to be at greater risk of heart disease and specific cancers. The study tracked almost 14,000 men over 38 years to determine the correlation between aerobic fitness and serious health complications.
How to improve your VO₂ max
The good news: unlike your actual age, you can lower your fitness age with the right kinds of activity. The most effective ways to raise VO₂ max include:
- HIIT (high-intensity interval training) — short intervals at 90–95% max heart rate with rest periods. The most efficient way to push VO₂ max up.
- Track sessions or tempo runs — sustained runs at a comfortably hard pace that develop cardiac output and lactate threshold.
- Zone-2 cardio — long, easy cardio at 60–70% max heart rate. Builds the aerobic base that supports higher VO₂ max.
- Strength training — supports overall cardiovascular efficiency and lean mass, both of which help.
- Consistency — 4–5 sessions a week for 8–12 weeks will move the needle. Sporadic training won't.
Ashwagandha, BOOST and VO₂ max
Research has shown that the adaptogenic botanical ashwagandha can meaningfully raise VO₂ max and improve athletic performance by improving heart and lung capacity:
- A systematic review of 4 controlled studies (161 adults) found ashwagandha supplementation (300–1,000 mg/day) significantly enhanced maximum oxygen consumption (VO₂ max).
- In a double-blind, randomised, placebo-controlled trial, healthy athletic adults taking KSM-66® Ashwagandha root extract (600 mg/day) saw significantly greater improvements in VO₂ max: +11.8% at 8 weeks and +13.6% at 12 weeks vs +4.5% for placebo. Quality-of-life scores also improved more in the ashwagandha group.
- A separate meta-analysis of 12 controlled studies (615 healthy adults) found ashwagandha (120–1,250 mg/day) enhanced physical performance including strength/power, cardiorespiratory fitness and fatigue/recovery.
If you're concerned about your VO₂ max or how to improve it, see a healthcare professional or qualified personal trainer.
Further reading
- Ashwagandha benefits: testosterone, stress, sleep & strength
- The complete 2026 UK guide to choosing a testosterone supplement
- How to boost testosterone naturally: 12 proven methods
- How to boost energy naturally: 12 science-backed methods
- Muscle recovery after workout: 10 science-backed methods
Advice is for information only and should not replace medical care. Consult a healthcare professional if you have any questions or are taking any other medications before you try any remedies or supplements.
