Training guide
VO2 max is the most oxygen your body can use in all-out exercise, and fitter people live longer on average: in large studies, low fitness predicted an earlier death as strongly as smoking or diabetes did. It falls with age, and faster the older you get, but it responds to training at any age, and those who start least fit gain the most.
Two honest caveats: no trial has yet shown that raising it makes you live longer, and the number on your watch is an estimate that can be well out for any one person.
This guide gives typical scores by age and sex from large lab studies, what the links with lifespan do and don't show, how far to trust your watch's number, and the training that raises VO2 max most, with a follow-along 4x4 interval workout.
VO2 max (maximal oxygen uptake) is the most oxygen your body can take in and use per minute in all-out exercise, given in millilitres per kilogram of body weight per minute (mL/kg/min). A lab measures it with a mask during a treadmill or bike test.
In US lab tests, the middle score was 48 for men and 38 for women in their 20s, falling to 24 and 18 in their 70s; Norwegian volunteers scored higher. The fall speeds up with age, from 3 to 6% a decade in your 20s and 30s to more than 20% a decade in your 70s.
Each extra 1 MET of fitness (a metabolic equivalent: 3.5 mL/kg/min) is linked with an 11 to 17% lower risk of death. These are observational links: the one long trial of exercise training found no significant effect on death rates, with a trend favouring intervals.
Regular aerobic training adds about 5 mL/kg/min in healthy adults, the least fit gain the most, and long intervals such as the 4x4 (four 4-minute hard efforts) raise it most.
Exercise-based watch estimates were right on average but out by up to about 10 mL/kg/min for individuals, and the Apple Watch read about 6 low in two studies. Follow the trend, not the number.
Your muscles use oxygen to make energy for hard, sustained work. VO2 max is the ceiling on how much oxygen your body can take up and use, so it reflects how well your heart, lungs, blood and muscles work together. It's measured on a treadmill or bike, with a mask that analyses your breath, during a test that gets harder until you can't go on; treadmill tests give higher values than bike tests.
Fitness is also given in METs (metabolic equivalents): 1 MET is 3.5 mL/kg/min, roughly the oxygen you use at rest, and 1 MET more fitness is roughly what it takes to run 1 km/h faster.
In trained men, gains after interval training matched gains in stroke volume (the blood the heart pumps with each beat). In another trial, gains depended mainly on a rise in the body's haemoglobin, the oxygen carrier in blood.
Scores are in mL/kg/min from lab treadmill tests, rounded to whole numbers. Watch scores can differ.
From the FRIEND registry: 7,783 treadmill tests in healthy US adults, published in 2015. Each line gives the middle value, the range covering the middle half of men (25th to 75th percentile) and where the top 10% begins:
Source 1
From the same registry, for women:
Source 1
A 2022 update of the same registry, with 22,379 tests, put treadmill values 1.5 to 4.6 mL/kg/min lower than the 2015 figures; its full tables weren't available to us, so the lists above are the 2015 ones.
In Norway's HUNT study of 3,816 healthy volunteers, values were higher, perhaps partly because fitter people volunteer, as the authors note. Their averages:
Followed for a median of 7.9 years, 810 healthy adults lost VO2 max at 3 to 6% a decade in their 20s and 30s, speeding up to more than 20% a decade in their 70s, whatever their activity level. Across age groups, reference values drop by about 3.5 to 4 mL/kg/min a decade.
There's no single cut-off. The fairest comparison is with people of your age and sex: above the middle value is above average, and the top quarter is high (our reading). Watches compare you with their own reference groups, so their labels can differ from these figures, and we found no UK-wide lab reference values.
Source 1
Across 199 cohort studies with 20.9 million observations, people with high fitness had about half the risk of death of those with low fitness, and each 1 MET higher was linked with an 11 to 17% lower risk (certainty very low to moderate). In 122,007 people having treadmill tests, the least fit had 5 times the death rate of the fittest, with no upper limit of benefit, and below-average fitness carried as much risk as smoking or diabetes. In 750,302 US veterans, the least fit had 4 times the risk.
In 93,060 veterans, changes in fitness of 1 MET or more went with proportional changes in death rates; in people with low fitness, a fall of more than 2 METs was linked with a 69 to 74% higher risk. In 11,530 UK Biobank adults, each 1 mL/kg/min gained per year was linked with a 15% lower risk of heart and circulatory disease. These are still observational links.
Generation 100 is the only long randomised trial of exercise training and death rates. Over 5 years, 1,567 people aged 70 to 77 did supervised training twice a week or followed the national activity guidelines; death rates didn't differ significantly, though the interval group had a trend towards fewer deaths. Fitness may partly reflect good health and genes rather than cause a longer life (our reading).
Source 5
The American Heart Association calls for fitness to be assessed routinely in clinical care, like blood pressure, and calls it a potentially stronger predictor of death than smoking, high blood pressure, high cholesterol or type 2 diabetes.
Source 21
Starting points, not prescriptions. Each names its trial or says it's our suggestion.
In healthy adults, steady endurance training raised VO2 max by about 4.9 mL/kg/min and high-intensity interval training (HIIT) by about 5.5, roughly 1.5 METs (our arithmetic). The least fit gain the most, women gained more in percentage terms, and the ability to adapt lasts through life.
Intervals of 2 minutes or more, with at least 15 minutes of hard work a session, gave the biggest advantage over steady training. The 4x4 (four 4-minute efforts reaching 90 to 95% of maximum heart rate, with 3 minutes easy between) raised VO2 max by 7.2% in 8 weeks done 3 times a week (Helgerud 2007). In a review of 353 studies, total training load and the number of sessions drove the gains: 6 sessions a week beat 4, and 4 beat 2.
Our editorial starting point: one 4x4 session a week plus 2 or 3 steady sessions, building to two interval sessions with an easier day between if you want more. Generation 100 used intervals twice a week, and Helgerud 3 times.
Within weeks. Fitness rose 12% in 6 weeks with stair sprints in inactive women, 10 to 14% in 8 weeks with 1-minute intervals in inactive adults, 10% in 4 weeks with the 4x4 in heart patients, and 7% in 8 weeks with the 4x4 in trained men.
People vary: in a 20-week programme, gains ranged from almost nothing to over 1 litre of oxygen a minute, and up to about half of that variation ran in families. About 20% of people may not gain at guideline doses, but in a trial of 78 adults, adding two sessions a week brought everyone along.
In Generation 100, VO2 max held steady over 5 years in all three groups, including the people following the national activity guidelines, against an expected age-related fall of at least 3.5 mL/kg/min (the researchers' estimate).
Source 5
Watches don't measure oxygen. Some estimate VO2 max from your resting heart rate and heart rate variability plus details such as your age and weight; others compare your heart rate with your speed during outdoor walks or runs (Firstbeat's method, used in Garmin and Fitbit watches). Firstbeat claims an error of about 5% for running; independent studies found 8 to 10%.
Source 10
Across 14 studies, mostly of young, active adults, exercise-based estimates were right on average, but for an individual they could be out by about 10 mL/kg/min either way. Resting-based estimates read about 2 high, with errors from about 13 low to 17 high. The Apple Watch read about 6 mL/kg/min low in two studies of 30 and 40 adults, putting only 14% in the right fitness band, and a Garmin Forerunner 245 read about 4 to 5 low, and about 6 low in highly trained athletes.
The individual error is bigger than the changes of 1.75 to 3.5 mL/kg/min that are linked with meaningful differences in health. So use one device, the same kind of outdoor walk or run, and watch the trend over months (our suggestion). A falling estimate isn't a diagnosis, but breathlessness that gets worse during normal activities is a reason to see a GP.
Any of these works if it gets you breathing hard for 4 minutes at a time; uphill walking on a treadmill suits people who don't run (our suggestion).
3D demoStationary cyclingBeginner · Cardio machine
3D demoIndoor Rowing (Rowing Machine)Beginner · Cardio machine
3D demoTreadmill runningIntermediate · Cardio machine
3D demoTreadmill walkingBeginner · Cardio machine
3D demoAir bike intervalsAdvanced · Cardio machine
3D demoStair climbingIntermediate · A stepThe Norwegian 4x4 is the long-interval session from the trials. The easy cardio workout builds the steady minutes that also raise VO2 max, and the build-up interval walk is the gentle way in.
The Norwegian 4x4, a well-studied interval session for raising VO2 max: four 4-minute hard efforts with 3 easy minutes between, on a bike, rower or treadmill.
40 minIntermediate3 movesCardio machine, A wallA 25-minute interval session on a bike or rower: one-minute hard efforts with two minutes easy, building from 4 to 8 rounds.
25 minIntermediate1 movesCardio machineA steady 30 to 45 minute cardio session at talk-but-not-sing pace: walk, cycle, row or cross-train, counting toward weekly activity guidelines.
40 minBeginner3 movesCardio machine, A wallA 20-minute no-equipment HIIT workout: jumping jacks, jump squats, mountain climbers, burpees, skips and bear crawls.
20 minIntermediate10 movesNo equipmentA 25-minute walk with short faster bouts: notice your heart and breathing speed up, then settle. A gentle way to get used to the feelings of effort.
25 minBeginner5 movesCardio machine, A wallBoth have an interval day on Saturday and steady cardio during the week; use the Norwegian 4x4 for the interval day if raising VO2 max is your goal (our suggestion).
A 3-day strength plan for men over 40 with power and bone work, two cardio days and mobility, built on research on ageing muscle.
3 training days45 minBeginner7 days a weekA full week that mixes intensities: three strength days, two cardio days, a mobility day and an easy day, never seven hard days.
3 training days45 minBeginnerHard intervals are safe for most people when built up gradually; our HIIT guide covers who should check first in detail. On a beta blocker, go by how hard it feels, not heart rate targets. Talk to your GP before hard training if:
Stop and call 999 for:
Get advice the same day for:
A lower score on your watch isn't a reason to worry on its own, because the estimates are imprecise. See a GP for:
It estimates it: right on average for groups, but out by up to about 10 mL/kg/min for individuals, and the Apple Watch read about 6 low in two studies.
Up to about half the variation in how much people improve runs in families, but nearly everyone improves with enough training, at any age.
Fitness is strongly linked with a longer life in observational studies, and changes in fitness track changes in risk, but the one long trial of training found no significant effect on deaths. The link is strong; cause and effect isn't proven.
The ability to adapt lasts through life. HIIT improved fitness in 44 trials of adults over 60, and people aged 70 to 77 trained with intervals for 5 years in Generation 100.
Steady training raised it by about 4.9 mL/kg/min, against about 5.5 for HIIT, in healthy adults. Intervals add a little on top.
Source 6
It's the most oxygen your body can take in and use per minute during all-out exercise, measured in millilitres per kilogram of body weight per minute. It reflects how well your heart, blood and muscles work together, and a lab measures it with a mask during a treadmill or bike test.
It depends on your age, sex and who you compare yourself with. In US lab tests the middle value was 48 for men and 38 for women in their 20s, 33 and 23 in their 50s, and 24 and 18 in their 70s; Norwegian volunteers scored higher. Being above the middle for your age and sex is a fair definition of good.
Do regular aerobic exercise and add one or two interval sessions a week. In trials, steady training raised VO2 max by about 5 mL/kg/min and intervals a little more, with longer intervals such as the 4x4 doing best. The least fit improve the most.
Weeks. Trials found gains of about 7 to 14% after 6 to 8 weeks of interval training, and about 10% after 4 weeks of 4x4 sessions in people with heart disease.
Roughly right on average, but not for your exact number. In two studies the Apple Watch read about 6 mL/kg/min low, and exercise-based estimates like Garmin's were right on average but could be out by about 10 for an individual. Use one device and watch the trend over months.
People with higher fitness live longer on average: each 1 MET (3.5 mL/kg/min) higher is linked with an 11 to 17% lower risk of death. These are observational links, which health and genes may partly explain, and the one long trial of exercise training found no significant effect on death rates, with a trend favouring intervals.
It falls slowly in early adulthood and faster later, by more than 20% a decade in your 70s, mainly because less oxygen is delivered and used with each heartbeat. In the Generation 100 trial, people aged 70 to 77 who trained, and those who followed the activity guidelines, held their VO2 max steady for 5 years, against the decline the researchers expected.
Yes. Many interval trials used exercise bikes, and rowing, stair climbing or uphill walking work if they get you breathing hard. Three 20-second stair sprints, three days a week, raised fitness 12% in 6 weeks in previously inactive women.
Partly: up to about half the variation in how much people improve with training runs in families. But when people trained more often, everyone improved.
It's an estimate, usually worked out from your heart rate against your speed during walks or runs, plus details such as your age. It's useful for following a trend, but it can be several points out for any one person.
Exercise education, not a personal prescription, and clinical review of these guides is pending. Check with a GP before starting hard training if you have a heart condition, chest pain, dizziness or breathlessness when active, and stop for sharp or increasing pain. Health disclaimer.
