VO2max

What is VO2max?

VO2max is the maximum amount of oxygen your body can take in, transport, and use during all-out exercise. It's measured in millilitres of oxygen per kilogram of body weight per minute (mL/kg/min). The number reflects how well your lungs, heart, blood vessels, and mitochondria work together to deliver and consume oxygen. In practical terms, a higher VO2max means you can sustain more intense physical work before exhaustion. It's the gold standard for measuring cardiorespiratory fitness, and research over the past two decades has made it clear that VO2max is also one of the strongest predictors of how long you'll live.

Why VO2max predicts mortality better than almost anything else

A 2018 study of 122,007 patients published in JAMA Network Open found that low cardiorespiratory fitness carried a greater mortality risk than smoking, diabetes, or coronary artery disease ^[1]. People who moved from the bottom 25% of fitness to above-average reduced their mortality risk by roughly 50%. Those in the elite fitness category (top 2.3%) had a 5-fold survival advantage over the least fit group. There was no upper ceiling to the benefit -- more fitness always meant less risk ^[1].

A separate meta-analysis covering over 20.9 million observations confirmed that each 1-MET increase in cardiorespiratory fitness (about 3.5 mL/kg/min of VO2max) was associated with an 11-17% reduction in all-cause mortality ^[2]. Peter Attia has made this data practical: he recommends training to keep your VO2max in the top quartile for your age, or better yet, at the level of someone 20 years younger.

VO2max, brain health, and biological aging

The benefits go beyond heart health. Higher VO2max is associated with thicker cortical tissue and better-preserved cognitive function in aging adults ^[3]. People with lower VO2max show faster trajectories of cognitive decline, particularly in memory ^[4]. One study found that men with low cardiorespiratory fitness had nearly double the risk of dementia compared to those with high fitness ^[5]. At the cellular level, a 2025 meta-analysis showed that individuals with VO2max at the 70th percentile or above had significantly longer telomeres, the protective caps on chromosomes that shorten as we age ^[6].

Understanding your numbers

Average VO2max for sedentary adults is about 35 mL/kg/min for men and 27 mL/kg/min for women, declining roughly 10% per decade after age 25. After 50, the decline accelerates to about 15% per decade in sedentary people. However, 50-70% of this decline is preventable through consistent training. Well-trained recreational athletes typically hit 45-55 mL/kg/min, while elite endurance athletes exceed 70-85 mL/kg/min. Even modest improvements of 3-5 mL/kg/min translate into meaningful mortality risk reduction.

How to test your VO2max

The gold standard is a graded exercise test (spiroergometry) with indirect calorimetry in a lab. You wear a mask that measures oxygen consumption and CO2 output while exercising at increasing intensity on a treadmill or bike until exhaustion. The test typically lasts 10-20 minutes. Wearable estimates from Garmin and Apple Watch provide useful trend tracking, but validation studies show error rates of 6-10% compared to lab values, especially at higher fitness levels ^[7]. For serious health optimization, get a lab test at least once a year and use your wearable for day-to-day tracking.

Training strategies to improve VO2max

Two complementary approaches work best together:

Zone 2 training: the aerobic foundation

Zone 2 training means sustained effort at 60-70% of your maximum heart rate, an intensity where you can hold a conversation but with effort. It builds mitochondrial density, improves fat oxidation, and expands the capillary networks in working muscles. This is the aerobic base that makes everything else possible. Aim for 150-200 minutes per week across 3-5 sessions of cycling, jogging, brisk walking, or rowing.

High-intensity interval training (HIIT) for VO2max

While zone 2 builds the base, VO2max itself improves most from intervals at 90-95% of maximum heart rate. The Norwegian 4x4 protocol (four 4-minute intervals at 90-95% max HR with 3 minutes of active recovery) has strong research support, with studies showing 5-10% VO2max improvements over 8-12 weeks. One to two HIIT sessions per week is enough for most people. A meta-analysis found a mean VO2max increase of about 16% from structured endurance training in older adults, showing that it's never too late to improve ^[8]. Key principles:

• Accumulate 12-20 minutes of total time at 90-95% max HR per session
• Use large muscle group activities (running, cycling, rowing) that sustain high cardiac output
• Prioritise consistency over intensity; one quality HIIT session per week beats three poorly executed ones
• Monitor recovery via HRV; declining trends signal accumulated fatigue
• Combine with 3-4 zone 2 sessions for the 80/20 polarised training approach used by elite endurance coaches