The Cooper test, a 12-minute run for VO₂max

What is the Cooper test?

Kenneth Cooper published the 12-minute run in JAMA in 1968.^[1] He tested 115 United States Air Force men in two ways. Each man ran as far as he could in 12 minutes. Each man also ran a treadmill test in a lab that measured the most oxygen he could use.

The test asks one thing of you. Run as far as you can in 12 minutes. The distance goes into an equation, and out comes an estimate of your VO₂max. VO₂max is your aerobic capacity, the most oxygen your body can use when you go all-out.

The Cooper test is a fitness benchmark. It is an all-out effort, so pick a day when you feel fresh and your legs are rested.

How do you run the Cooper test?

1. Go to a 400-meter track if you can. Open sky and flat ground give the cleanest distance, and you can count your own laps as a check.
2. Warm up with easy jogging until your legs feel loose. Finish with a few short bursts of faster running so your legs are ready to run hard.
3. Start an outdoor run on your watch and a 12-minute timer.
4. Run as far as you can in 12 minutes. Hold one even pace and use whatever you have left in the last minute.
5. Stop when the timer ends and note the spot. Add your full laps to the part of the last lap.
6. Jog or walk easy for a few minutes to cool down.

Pacing decides the result. A fast first lap that you cannot hold usually ends with a shorter distance than an even run.

A few things make the distance wrong. A net downhill or a strong tailwind adds distance that does not come from your fitness. Tall buildings, heavy tree cover and tunnels make GPS drift. A track avoids most of these, because the laps are a fixed length.

How do you turn your distance into VO₂max?

This is the line researchers call Cooper's equation, and you can run it yourself on your own distance.^[2]

VO₂max = 22.351 × distance in kilometers − 11.288

The answer comes out in mL/kg/min. That means milliliters of oxygen for each kilogram of body weight each minute. If you measured in miles, the same line reads 35.970 × miles − 11.288.

Here is one worked example. Say you ran six laps of a 400-meter track, which is 2,400 meters.

1. 2,400 meters is 2.4 kilometers.
2. 22.351 × 2.4 = 53.6424.
3. 53.6424 − 11.288 = 42.3544.
4. Your estimate is about 42.4 mL/kg/min.

Every 45 meters of distance moves the estimate by about one point, because 1,000 divided by 22.351 is 44.7. That is why a track helps. GPS drift of half a lap can move the answer by about four and a half points.

A distance far from what your usual pace would give often points to a GPS problem or a stopped workout. Check the route before you trust the number.

How close does a 12-minute run get to a lab test?

Cooper's own result was strong. The 12-minute distance and the lab result in his 115 Air Force men had a correlation of 0.897.^[1] A correlation of 1 would mean the two always rise and fall together. A correlation of 0 would mean no link at all.

Later studies found a looser link. A 2016 review pooled 26 results from 1,204 people. The 12-minute test scored 0.78 against lab tests.^[3] That was the highest score of the tests in the review that run for a set time. Sex, age and fitness level did not seem to change how well these tests worked. The authors remind readers that a field test gives an estimate. Only a lab test measures VO₂max directly.

Single studies found the estimate landing above the lab number in some groups and below it in others.

• The Cooper estimate averaged 60.6 mL/kg/min in 22 young men who exercised regularly. Their lab treadmill test averaged 60.1.^[4]
• The estimate averaged 6.0 points below a lab treadmill test in 73 college team-sport athletes. Nearly every athlete landed somewhere between 19.8 points below and 7.9 points above.^[5]
• The estimate averaged 3.0 points above a lab test on a bike in 58 inactive male students.^[2]
• A study of 21 young adults found the estimate read low for people with lower lab results and high for people with higher ones.^[6]

So the line puts a group of people in about the right order. One person's number can still miss by several points in either direction. Your number is most useful when you compare it with your own next test on the same track.

What changes your distance from one test to the next?

Repeat tests agree closely when nothing else changes. One study had 60 young adults do the 12-minute run three times and a shuttle run test three times. The repeat results lined up closely across both tests. Their reliability score was 0.96 out of 1.^[6]

Sleep moves the distance. Twenty young runners did a 12-minute run after a full night of 8 hours in bed and again after only 4 hours. They covered about 6% less distance after the short night.^[7] Six percent of 2,400 meters is about 144 meters. That moves the estimate by more than three points.

Keep the conditions the same each time. Use the same track, a similar time of day and a similar training day before it. Then a longer distance is more likely to mean you got fitter.

VO₂max takes weeks to move. Clear gains showed up by the end of 8 weeks of training in the study behind the Norwegian 4x4 workout.^[8] A second test after about 8 weeks of regular training gives a real change time to show.

What else can your 12-minute distance tell you?

A Cooper distance also tracks race times. One study followed 198 recreational runners who ran the Cooper test 7 to 10 days before a half marathon.^[9] A longer Cooper distance went with a faster half marathon. The correlation was minus 0.906. The minus sign only means that more meters went with fewer minutes.

The same study built an equation from the test. It predicted half-marathon time with a typical error of about 5 minutes. Most of the runners in that study were men around 40 years old.^[9]

What is a good Cooper test score?

A good Cooper score is one that beats your own last test on the same track. A longer distance after a block of training is a clear sign that your training is working.

Many charts online turn a 12-minute distance into a grade word for your age and sex. A grade word hides the number. The number is what you compare the next time you run the test.

One test is one point on a line. It tells you where you are today. A second test after weeks of training tells you which way you are moving.

The VO₂max by age guide shows where your number lands among people of your age and sex who took a lab test.

Does the Cooper test show your max heart rate?

The finish gives you a floor for your max. Push the last minute as hard as you can, and the top heart rate near the finish is a measured number. Your max heart rate is at least that high.

That number is a better starting point than a guess from your age. A study of 3,320 healthy adults found that a max predicted from age alone had a typical error of about 11 beats a minute.^[10]

A hard finish can reach as high as a lab test does. One study of 104 adults found the top heart rate in the 12-minute run averaged about 184 beats a minute. The same people averaged about 180 in a lab treadmill test.^[11] That lab test could stop before a person reached their highest heart rate, so neither average is sure to be a true max.

Your true max can still be higher than the peak you saw. One peak only shows how high your heart rate went that day. Type the peak from your finish as your max below, and the bands redraw from a measured number.

The guide to finding your max heart rate covers more ways to find it, and how to read the peak your watch saved.

Where Diastra fits

Diastra reads every workout your Apple Watch saved. It finds your max heart rate from your own workouts, a guided max heart rate test or a number you type, and it tells you which one it used. Easy, Threshold and VO₂max are drawn from that max. Diastra also shows over the weeks whether your training is working ("Getting fitter. Holding steady. Slipping."), even when the answer is no.