What Is VO2 Max?
A proper VO2 max test asks for 8 to 12 minutes of climbing workload behind a mouthpiece and a nose clip, and the figure it produces is the peak rate at which the body can take in, deliver and use oxygen, given in milliliters per kilogram of body weight per minute.
Nike screened elite marathoners as candidates for a sub-two-hour race and the squad averaged 71.0, with the lowest man in the group at 62. The figure marked who was eligible for the project and said nothing about who would finish first.
What VO2 Max Measures
The metabolic cart beside the treadmill reads the air a runner moves and the oxygen and carbon dioxide fractions inside it, then subtracts what comes back out from what went in. It reports the oxygen consumed by working tissue. Lung capacity is not being read, and neither is effort.
The value comes from two quantities multiplied together. Cardiac output, the blood the heart moves each minute, is multiplied by the arteriovenous oxygen difference. That difference is the oxygen the muscle strips out of the blood on the way past. Cardiac output is itself heart rate times stroke volume, the blood pushed out per beat.
Maximum heart rate is close to immovable among those quantities. Training barely shifts it and age lowers it on a schedule of its own, which leaves stroke volume and oxygen extraction to account for the whole trainable share.
The absolute version in liters per minute matters most in rowing and flat cycling. Running quotes the relative one. Divide 4.9 liters a minute by 70 kg and the answer is 70 mL/kg/min. Losing weight raises the figure by shrinking the divisor, with nothing having changed inside the athlete.
How the Lab Test Works
The reference method is a graded exercise test to exhaustion on a treadmill or a bike, with expired air analyzed breath by breath. The nose clip forces breathing through the mouth alone. The subject cannot speak and cannot drink when they want to most. Technicians warn subjects in advance that they will drool.
Robert Bruce’s 1960s treadmill test raises speed and gradient together every three minutes, in steps large enough that some subjects fail on leg fatigue first. Ramp protocols lift the workload every few seconds instead, producing one long smooth climb. Both are built to bring a subject to exhaustion inside 8 to 12 minutes.
Collecting expired air in canvas Douglas bags in 1923, Archibald Hill and Hartley Lupton found that uptake climbed with running speed to a point and then stopped rising however fast the runner went. Uptake that levels off marks a true maximum instead of the highest reading of the day.
Modern ramp tests frequently produce no such leveling, since many subjects reach exhaustion with uptake still climbing. Laboratories responded with secondary criteria, a ratio of carbon dioxide produced to oxygen used above a set value, a heart rate near the age-predicted maximum, a blood lactate above roughly 8 mmol/L. The criteria fail in both directions. A test stopped the moment that ratio passes 1.10 underestimates the value, while a plateau read too readily overstates it. In adolescents, 71% of apparent plateaus appeared during sub-maximal exercise.
The current fix adds another bout, run after a recovery period as a short constant-load effort above the highest stage. If uptake does not exceed the ramp value, the ramp value stands. A figure with no plateau and no confirmation behind it is properly labeled VO2 peak, which covers most of the numbers in circulation.
Are Smartwatch Estimates Accurate?
A wrist-worn device estimates the figure from heart rate against external workload, pace from satellite positioning or power from a paired meter, across stretches where heart rate is above roughly 70% of maximum. Because nothing in that chain measures oxygen, an error in the maximum heart rate the model is anchored to appears directly in the output.
Against laboratory gas analysis an Apple Watch underestimated by a mean of 6.07 mL/kg/min, and for an individual the error spanned 6.11 too high to 18.26 too low. The tightest accuracy claim in that literature belongs to an algorithm’s own manufacturer.
Flat fast running returns a higher estimate than the same effort on hills, because the algorithm reads pace against heart rate and a gradient breaks that relationship. Forums record a figure jumping from 59 to 72 after one indoor session, and dropping from 48 to 33 in a week after a device change, the training unchanged.
Average and Elite Scores by Age
Median values from more than 80,000 maximal treadmill tests fall from 48.0 mL/kg/min at 20 to 29 to 24.4 at 70 to 79 for men, from 37.6 to 18.3 for women. Clinical sources give 5 to 10% per decade and popular coverage gives 10%, against nearer 5% for masters athletes who keep their training intensity. Outside those medians entirely, the highest value ever published, 96.7, was measured on the Norwegian cyclist Oskar Svendsen at 18, and the laboratory sent its equipment back to be checked before publishing it.
How Much VO2 Max Can Improve
A sedentary adult starting out can expect 10 to 20% inside 8 to 12 weeks, while a trained athlete near the ceiling gains 1 to 5% for a season of the same work.
A 1999 study put 481 sedentary adults from 98 families through 20 weeks of supervised cycle training, measured twice before and twice after. Mean improvement was about 400 mL a minute. Underneath that average, individual responses ran from essentially nothing to more than a liter a minute. Roughly 7% of subjects gained 0.1 L/min or less. Variance between families was 2.5 times the variance within families, and heritability of the response came out around 47%.
That describes one adaptation, on one protocol, over 20 weeks, and does not mean the low responders are stuck. A single-subject report documents a 96% gain in a recreational athlete across 24 months. Matt Carpenter’s own figure climbed from 57 in college across a career of racing. Both cases start low and run long.
Does VO2 Max Predict Race Performance?
The candidates Nike gathered for a sub-two-hour marathon measured between 62 and 84 in the published screening data, against the 70 to 85 mL/kg/min elite endurance athletes are usually quoted at.
Carpenter tested at 90.2 in 1990 and 94.9 in 1994, the highest figure ever measured in a runner. He never broke 2:15 for a flat road marathon, though he won Pikes Peak repeatedly and ran the Everest Marathon in 2:52.
Two athletes with matched ceilings finish minutes apart because two other quantities are in play. Lactate threshold is the fraction of that ceiling a runner can sustain for a long stretch, and running economy is the oxygen cost of covering a given distance at a given speed. Secondary summaries of the Costill-era work put Derek Clayton, marathon world record holder in the late 1960s, at about 69.7 and Frank Shorter, the 1972 Olympic champion, at about 71.3. Both men were among the most economical runners ever studied. Clayton stayed at roughly 80 to 85% of his own ceiling through a marathon, a fraction most runners cannot reach.
None of that makes the figure ornamental. Over efforts of roughly 3 to 30 minutes coaching literature treats it as the quantity that matters most. It tells a sedentary adult apart from a trained one without difficulty and loses its power only between two trained athletes. Away from sport, an analysis of 122,007 patients tested at the Cleveland Clinic found cardiorespiratory fitness inversely associated with all-cause mortality with no observed upper limit of benefit, in a group referred for clinical testing.
The source of running economy is still argued. Tendon stiffness, limb proportions and accumulated years of mileage all appear in the explanations, though no laboratory sells a test for economy, and which of those a runner could deliberately change is not yet answered.