Is a VO2 Max of 42 Good? What the Number Means

A VO2 max of 42 mL/kg/min falls close to the population-wide average, but whether it qualifies as “good” depends heavily on your age and sex. A large study of nearly 4,000 healthy adults found that the overall mean VO2 max was about 41 mL/kg/min, with men averaging around 45 and women around 37. So 42 lands in different territory depending on who you are: solidly above average for a 40-year-old woman, but below average for a 25-year-old man. The number matters more than most people realize, though, because VO2 max is one of the strongest predictors of how long you live.

How Age and Sex Shift the Goalposts

VO2 max measures the maximum rate at which your body can use oxygen during intense exercise, expressed in milliliters of oxygen per kilogram of body weight per minute. The higher the number, the more aerobic work your cardiovascular and muscular systems can sustain. But “good” only makes sense relative to a reference group, and the two biggest factors shaping that reference are age and sex.

In a study of 3,816 healthy Norwegian men and women aged 20 to 90, the highest values appeared in the youngest group. Men in their twenties averaged about 54 mL/kg/min, and women in the same age range averaged about 43. From there, both sexes lost roughly 3.5 mL/kg/min per decade, amounting to about an 8% drop every ten years. By the time someone reaches their sixties or seventies, an “average” VO2 max is considerably lower than a young adult’s average.

This means a 42 for a 55-year-old man is solidly in the upper range for his peers, while the same number for a 22-year-old man places him below the group average. For a woman in her thirties, 42 is well above average. Context is everything, and any chart or app that just labels 42 as “fair” or “good” without accounting for your demographics is giving you incomplete information.

British population data confirms that the decline is not perfectly linear, either. In men, the centile curves dropped fairly steadily until the late sixties and seventies. In women, those in the upper fitness percentiles actually peaked between ages 30 and 40 before declining more steeply.

Why Men and Women Have Different Averages

The roughly 19% gap between male and female VO2 max values often gets attributed vaguely to “men are bigger,” but the actual mechanisms are more specific. Research using invasive physiological methods in highly trained athletes has shown that the primary drivers of the sex gap are differences in body composition and hemoglobin concentration. Men carry more lean mass relative to total body weight and have higher hemoglobin levels, which means more oxygen-carrying capacity per liter of blood.

A study of young Indian national hockey players broke down the contribution further, finding that body mass index, body fat percentage, and hemoglobin concentration together accounted for most of the sex-based difference in VO2 max when expressed relative to lean body mass.

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The practical takeaway is that comparing your VO2 max to values from a mixed-sex chart is misleading. A woman with a VO2 max of 42 is physiologically fitter relative to her peers than a man with the same number. Always look at sex-specific percentiles when evaluating your own score.

The Body Weight Problem

Because VO2 max is typically divided by total body weight, the number penalizes people who carry extra fat. Fat tissue consumes very little oxygen during exercise but adds to the denominator. A study comparing lean and obese children found that absolute VO2 max was actually higher in the obese group, but VO2 max relative to body weight was substantially lower. When the researchers expressed it relative to fat-free mass instead, the difference between the two groups disappeared.

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This has real implications. If you weigh 100 kg and carry 25 kg of body fat, your VO2 max per kilogram of total weight will look worse than someone at 75 kg with the same cardiovascular engine. Your heart and lungs may be doing identical work, but the standard metric doesn’t reflect that. Some researchers have argued that lean mass rather than total body weight is the more appropriate way to scale VO2 max, and that the conventional formula systematically underestimates the aerobic capacity of heavier individuals.

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If you have a VO2 max of 42 and you’re carrying significant extra body fat, losing fat without losing muscle could push your number up meaningfully even without any change in actual cardiovascular fitness. The reverse is also true: someone who gains lean muscle mass rapidly may see their VO2 max per kilogram dip slightly, not because their heart got worse but because muscle is heavier than what their oxygen delivery system can proportionally feed.

What VO2 Max Tells You About Longevity

The reason clinicians and researchers care so much about VO2 max goes well beyond athletic performance. The American Heart Association has called for cardiorespiratory fitness to be treated as a clinical vital sign, akin to blood pressure or heart rate.

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A landmark study following over 120,000 patients who underwent treadmill testing found that low fitness was a stronger predictor of death than smoking, diabetes, or coronary artery disease. People in the lowest fitness group had roughly five times the mortality risk compared to elite performers. Even moving from below-average to above-average fitness was associated with a meaningful reduction in death risk.

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A more recent analysis spanning multiple age groups, races, and both sexes confirmed this pattern. The lowest mortality risk appeared at very high fitness levels, and there was no point at which getting fitter started to increase risk. People in the bottom fifth of fitness had about four times the death rate of the fittest group.

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What makes this especially relevant if you’re sitting at 42 is that the biggest mortality benefit comes from moving out of the lowest fitness categories. The jump from sedentary to moderately active is the most dramatic and reproducible finding in the exercise science literature.

¹⁰ A score of 42 already places most people well above the danger zone, but pushing higher still carries continued benefit. These observational findings do come with caveats: fitter people may exercise more partly because they are healthier to begin with, making it hard to fully separate cause and effect.

Functional Independence in Older Age

Beyond mortality statistics, VO2 max has a practical connection to whether you can live independently as you age. A longitudinal study of older adults found that lower cardiorespiratory fitness at baseline increased the odds of becoming dependent in daily activities by about 14% for each 1 mL/kg/min decrease, even after controlling for disease and age.

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This finding reframes what a “good” VO2 max means for someone in midlife. If you’re 50 with a score of 42 and expect to lose roughly 3 to 4 points per decade, you’ll still be in a comfortable range at 70. If you’re 50 with a score of 30, the same rate of decline puts you much closer to the threshold where everyday tasks like climbing stairs or carrying groceries become genuinely difficult. Building a buffer now pays dividends decades later.

Lab Testing vs. Your Smartwatch

Most people encounter their VO2 max number on a smartwatch or fitness tracker, not in a laboratory. The gold standard measurement involves a cardiopulmonary exercise test, where you run or cycle to exhaustion while wearing a mask that analyzes every breath.

¹² Watches, by contrast, estimate VO2 max using heart rate data, pace, and algorithms. The question is how much you should trust those estimates.

The answer: treat them as a useful trend tracker, not a precise measurement. A validation study of the Apple Watch Series 7 found that the watch systematically underestimated VO2 max compared to lab testing, with individual-level reliability rated as poor. The average error was about 16%, meaning if the lab says you’re at 46, your watch might tell you 39 or 53.

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A study of the Garmin Forerunner 245 found the watch underestimated VO2 max by about 4 to 5 mL/kg/min on average, with the error being worse in highly trained athletes (about 10% off) and more accurate in moderately trained ones (about 3 to 4% off).

¹⁴ The Google Pixel Watch 3 showed low overall bias but wide limits of agreement at the individual level, meaning the average across many people was close, but any single person’s reading could be off by a large margin.

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So if your watch says 42, the real number could plausibly be anywhere from the high thirties to the mid-forties. The watch is better at telling you whether your fitness is going up or down over months than it is at nailing the absolute value. If you want to know your true number, you’ll need a lab test.

How to Improve Your VO2 Max

VO2 max is limited by a chain of systems working together: your lungs pulling in air, your heart pumping blood, your blood carrying oxygen, and your muscles extracting and using it. No single link in that chain acts as the sole bottleneck. In whole-body exercise like running, the heart’s pumping capacity tends to be the most important constraint, but muscles, blood volume, and mitochondrial density all play meaningful roles.

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Training improves both sides of the equation. On the cardiac side, sustained exercise increases the amount of blood your heart ejects with each beat. This was demonstrated even in patients with coronary artery disease, where 12 months of intense training produced an 18% increase in stroke volume during exercise.

¹⁷ On the peripheral side, exercise stimulates muscle capillary growth. A meta-regression found that endurance training, high-intensity intervals, and sprint training all increased the capillary-to-fiber ratio in skeletal muscle by roughly 10 to 15%.

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In terms of what kind of training works best, a meta-analysis of controlled trials found that high-intensity interval training produced slightly greater VO2 max improvements than traditional steady-state endurance training, though both methods led to large gains. The edge for intervals was small, around 1 to 2 mL/kg/min, and was more pronounced in older subjects, longer programs, and people with lower baseline fitness.

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If your VO2 max is currently 42 and you want to push it higher, the most evidence-backed approach is consistent aerobic training with some high-intensity work mixed in. The specific format matters less than the consistency and the willingness to occasionally work hard enough that conversation becomes impossible.

How Much of It Is Genetic

Your trainability is not entirely under your control. The HERITAGE Family Study, which put families through an identical 20-week training program, found that the heritability of the VO2 max training response was about 47% after adjusting for age, sex, and baseline values.

²⁰ That means roughly half the variation in how much people improve with the same program can be traced to genetic factors. Some people started the program with modest fitness and saw large jumps; others started at the same level and barely budged.

Genome-wide analyses have suggested this trainability is influenced by many genes, each with a small effect, rather than one or two master genes. Those findings have not yet been reliably replicated, so we cannot currently use a genetic test to predict how much someone’s VO2 max will rise with training.

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What this means practically is that if you’ve been training consistently for months and your VO2 max hasn’t budged from 42, it doesn’t necessarily mean you’re doing something wrong. You may simply be a low responder. That said, even low responders tend to see some improvement with longer programs and higher training volumes, and the health benefits of exercise extend well beyond what the VO2 max number captures.

The Age-Related Decline and How Training Slows It

VO2 max declines with age in everyone, but the rate of decline is not fixed. A study tracking master athletes and sedentary men over several years found that sedentary men lost about 12% of their VO2 max per decade, while master athletes who kept training lost only about 5.5% per decade, roughly half the rate.

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A review of masters athletes expanded on this, showing that the decline rate was tightly linked to changes in training volume. Men who maintained near-normal training volume lost only 5 to 6.5% per decade. Those who cut training by 11 to 20% saw declines of 8 to 26% per decade, and those who became mostly sedentary lost as much as 15 to 46% per decade. About 54% of the variation in decline was explained by training volume changes alone, rising to 70% when age was added to the model.

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The implication is straightforward: your VO2 max at 70 is shaped much more by what you do between now and then than by some inevitable biological clock. A 42 at age 40 with continued training could still be in the mid-thirties at 60. A 42 at age 40 followed by a sedentary decade could drop you into the mid-twenties, a range where daily functioning starts to feel effortful.

Brain Health and VO2 Max

An emerging line of research connects VO2 max to cognitive health. A study of healthy adults aged 60 to 72 found that higher VO2 max was associated with greater integrity of the locus coeruleus, a brainstem structure involved in attention, arousal, and stress responses. The locus coeruleus is one of the first brain regions affected in Alzheimer’s disease, and the researchers proposed that maintaining aerobic fitness may help build resilience against neurodegeneration.

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Separately, research in people with mild cognitive impairment found that higher VO2 max was linked to better white matter integrity in the brain and stronger executive function. The brain’s wiring, measured by diffusion imaging, looked healthier in fitter participants, and that healthier wiring correlated with better performance on tasks requiring planning and flexible thinking. This is still observational work, so the usual caveats about cause and effect apply. But it adds to a growing body of evidence that the cardiovascular system and the brain age as a unit, and that what protects one tends to protect the other.

Altitude and Other Environmental Curveballs

If you test your VO2 max in Denver and again in Miami, you’ll get different numbers. VO2 max drops as altitude increases because there is less oxygen available in the air. Research on endurance athletes found that both performance and VO2 max began declining from as low as 300 to 800 meters above sea level and continued to decrease linearly up to 2,800 meters.

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Training at altitude is sometimes used deliberately to boost VO2 max at sea level. The main mechanism appears to be an increase in red blood cell production triggered by the lower oxygen environment, which improves the blood’s oxygen-carrying capacity. Some evidence also points to changes at the gene-regulation level, including pathways involved in blood vessel formation and mitochondrial efficiency.

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For most people, the practical point is this: if your watch measured your VO2 max during a run at moderate altitude, the number may be somewhat lower than what you’d produce at sea level. Heat, humidity, and illness also temporarily suppress VO2 max scores without reflecting any real change in fitness. A single reading taken on a bad day or in tough conditions tells you little. Trends over weeks and months are far more informative than any one test.