Six-minute walk test (6MWT) predicted distance calculator

What the six-minute walk test measures

The American Thoracic Society (ATS) statement of 2002 says the six-minute walk test (6MWT) measures the distance a patient can walk quickly on a flat, hard surface in 6 minutes. It calls it a test of how the whole body copes with exercise, from the heart and lungs to the circulation and the muscles. It does not show which of these limits the patient, and it does not measure peak oxygen uptake.

Patients set their own pace and may stop to rest, which is why the ATS called it a submaximal test. The 2014 ERS/ATS technical standard adds that, in adults with moderate chronic respiratory disease, the 6MWT reaches a peak oxygen uptake close to a laboratory exercise test. That is why it adopted the contraindications used for that laboratory test (see below).

The ATS says the strongest reason to use the test is to measure the response to treatment in people with moderate to severe heart or lung disease. It is also used as a one-time measure of functional status and to predict morbidity and mortality.

How to do the six-minute walk test

These steps follow the ATS 2002 statement. You need a flat, straight indoor corridor with a hard surface and little foot traffic. The ATS course is 30 m long (a 100-foot hallway), marked every 3 m, with a cone at each turnaround point and a brightly colored starting line. Each lap there and back is 60 m. Do not use a treadmill: the ATS notes that treadmill results are not interchangeable with corridor tests.

Have a countdown timer, a lap counter, a chair you can move along the course, a source of oxygen, a blood pressure cuff, a telephone and an automated defibrillator ready.

1. The patient wears comfortable clothes and walking shoes, uses their usual walking aid and keeps to their usual medicines. They should not have exercised vigorously in the 2 hours before the test.
2. Skip the warm-up. The patient sits in a chair near the start for at least 10 minutes. Use this time to check for contraindications (see below) and to measure pulse and blood pressure.
3. Record baseline breathlessness and fatigue on the Borg scale. If you use a pulse oximeter, record baseline heart rate and oxygen saturation (SpO2).
4. Read the standard instructions. They begin: "The object of this test is to walk as far as possible for 6 minutes." They tell the patient: "You are permitted to slow down, to stop, and to rest as necessary. You may lean against the wall while resting, but resume walking as soon as you are able." Walk one lap to show the brisk turn around the cone, and remind the patient not to run or jog.
5. Start the timer as soon as the patient starts walking. Stand near the starting line and do not walk with the patient. Click the lap counter each time they cross the starting line.
6. Say only the standard phrases below, in an even tone. The ATS says not to use other words of encouragement, or body language to speed the patient up.
7. If the patient stops to rest, say: "You can lean against the wall if you would like; then continue walking whenever you feel able." Do not stop the timer.
8. At 6 minutes, say "Stop!" and mark the spot. Record the Borg scores again and ask: "What, if anything, kept you from walking farther?"
9. Total distance = number of laps × 60 m + the final partial lap. Round it to the nearest meter.

The 2014 ERS/ATS technical standard kept this approach but changed a few details. The course should be 30 m or longer, to match the courses used to build the reference equations. Continuous pulse oximetry is recommended, with the assessor walking behind the patient to read the lowest SpO2 without setting the pace. While a patient is resting, it adds a phrase every 30 seconds once SpO2 is 85% or higher: "Please resume walking whenever you feel able."

The other change is practice tests. The ATS in 2002 said a practice test is not needed in most clinical settings, but that if you do one, you should wait at least 1 hour and report the higher distance. The 2014 standard found a clear learning effect and says 2 tests must be done when the 6MWT is used to measure change over time, at least 30 minutes apart, with heart rate and SpO2 back to baseline before the second, and the better distance recorded. For a one-off measure, one test may be enough. If the distance is close to a cutoff that will guide a decision, the standard says to consider a second test.

Safety: contraindications and when to stop

The ATS 2002 statement lists 2 absolute contraindications: unstable angina during the previous month and myocardial infarction during the previous month. Its relative contraindications are a resting heart rate of more than 120, a systolic blood pressure of more than 180 mmHg and a diastolic blood pressure of more than 100 mmHg. Refer a patient with any of these to the doctor ordering or supervising the test before you go ahead. Review any resting ECG from the previous 6 months.

Stable angina on exertion is not an absolute contraindication. The ATS says such patients should do the test after taking their anti-angina medicine, with rescue nitrate medicine at hand.

The 2014 ERS/ATS standard uses a longer list. Because the test can raise oxygen uptake close to a maximal test, it adopted the contraindications for cardiopulmonary exercise testing. They are listed below from its Table 4, in American spelling. Here too, a patient with any of them is referred to the doctor ordering or supervising the test.

The two lists do not match on every point, and some 2002 limits are tighter. The 2002 statement counts unstable angina or a heart attack in the previous month as absolute contraindications, while Table 4 names acute myocardial infarction (3 to 5 days). Its relative contraindications include a resting heart rate above 120, and its blood pressure limits (above 180 mmHg systolic or 100 mmHg diastolic) are lower than those in Table 4 (above 200 or 120). Where the two differ, the cautious choice is the tighter limit: check with the doctor before you test.

The ATS lists the reasons for stopping a 6MWT straight away: chest pain, intolerable breathlessness, leg cramps, staggering, sweating (diaphoresis), and a pale or ashen appearance. The 2014 standard adds oxygen saturation. Stop the test if SpO2 falls below 80%. If it recovers to 85% or more, the patient may be asked to walk again.

If you stop a test, the patient sits or lies down as needed. Depending on how serious it looks, check the blood pressure and pulse oximeter readings, ask a doctor to assess the patient, and give oxygen as appropriate. Write down the distance, the time the patient stopped and the reason.

Run the test somewhere help can reach you fast. The ATS lists oxygen, sublingual nitroglycerine, aspirin and a salbutamol (albuterol) inhaler or nebulizer among the supplies to keep available. The tester should hold at least a Basic Life Support certificate. A patient on long-term oxygen walks with oxygen at their usual flow rate, and the same set-up is used at every retest.

The reference equations in this calculator

Enright and Sherrill tested adults from the Tucson Epidemiological Study of Airways Obstructive Disease in Arizona, USA. After leaving out people with a factor that lowered the distance walked (for example current smoking, diuretic use, a history of stroke, a body mass index over 35, or age over 80), 117 men and 173 women aged 40 to 80 remained in the healthy group. They walked in a 100-foot hallway with standard encouragement. The median distance was 576 m for men and 494 m for women.

The equations explained 42% of the variation in distance for men and 38% for women. The lower limit of normal is the 5th percentile: take 153 m off the predicted distance for men and 139 m for women. In 2020 the journal published a correction because the scatter plots for men and women had been printed as identical figures. The equations in the paper's Table 3 were not changed.

Enright and Sherrill warn against using their equations for people outside their group, including non-Caucasian people and people younger than 40 or older than 80. Their results apply to the first walk a patient does. They add that people who have done the test before, or who get non-standard encouragement, may walk farther.

The second option is the equation of Troosters, Gosselink and Decramer. They tested 51 healthy volunteers aged 50 to 85 in Leuven, Belgium, in a 50 m hospital corridor. Their method differs from the later ATS protocol: every 30 seconds, the volunteers were told how much time had passed and encouraged to keep walking as fast as possible.

Each person walked twice, about 2.5 hours apart, and the better walk was used. The second walk was on average 8% longer, and the first walk reached on average 91% of the predicted distance. So a patient who walks once, with the ATS phrases once a minute, will tend to get a lower percentage with this equation.

Their equation explained 66% of the variation, with a residual standard deviation of 56 m. They suggest that a distance below 82% of predicted can be considered abnormal. They also say the equation should be confirmed in larger populations. The printed equation in their paper has a misplaced bracket, but the definition of the sex term (1 for men, 0 for women) and the finding that men walked 84 m farther show that the 51.31 m term is added for men, as shown above. The group averages confirm it: with the term added, the equation gives about 628 m for the average volunteer, close to the 631 m the group walked; with it subtracted, it gives about 570 m.

How to read the result

Percent of predicted is the distance walked divided by the predicted distance, times 100. With the Enright and Sherrill equations, a distance below the lower limit of normal falls below the 5th percentile predicted for healthy people of the same sex, age, height and weight in their study.

A low distance does not tell you why it is low. The ATS calls a low 6MWD nonspecific and nondiagnostic, and says it warrants a thorough search for the cause. It suggests checking lung function, heart function, the ankle-arm index, muscle strength, nutrition, orthopedic problems and cognition.

To follow a patient over time, compare distance with distance. The ATS in 2002 recommended reporting change in meters (for example, "the patient walked 50 m farther") rather than as a change in percent of predicted. The 2014 ERS/ATS standard notes that the value of percent predicted for judging change over time has not been studied. It gives a minimal important difference of 30 m for adults with chronic respiratory disease. That figure comes from respiratory patients and may not apply to other conditions.

If you report percent of predicted, name the equation you used. The 2014 standard asks for this, because different equations give different predicted distances for the same person.

Limits of reference equations

The 2014 ERS/ATS standard found 16 studies from 1998 to 2013 with 6MWT reference equations from healthy adults. They used a wide range of populations and methods, with course lengths from 20 to 50 m and from 1 to 4 walks. Applied to one person, these equations give a wide spread of predicted distances. The standard recommends using an equation built and checked in the local population where possible.

Even in their own groups, the equations leave a lot unexplained. Enright and Sherrill's models left about 60% of the variation in distance unexplained. Method matters too: the ATS lists a shorter corridor, older age, shorter height, higher body weight, female sex and impaired cognition among the factors that reduce the distance, and high motivation or a previous test among those that increase it.

An equation built in one population may not fit another. As one example, Ramanathan and Chandrasekaran (2014) built equations from 125 healthy volunteers aged 25 to 80 at one hospital in India, tested on a 30 m course following the ATS statement. They reported that equations from Western populations predicted longer distances than their volunteers walked, which would make percent of predicted look lower. The Enright equation they compared with was a later one (Enright and colleagues, 2003), not the 1998 equation used here. Their own equations explained about 28% of the variation in distance, and the authors noted a weaker fit and a convenience sample.

Keep your own method the same when you retest a patient: the same course, the same phrases, the same oxygen set-up and the same walking aid. The 2014 standard notes that the distance is very sensitive to each of these.

References

1. ATS Committee on Proficiency Standards for Clinical Pulmonary Function Laboratories. ATS statement: guidelines for the six-minute walk test. American Journal of Respiratory and Critical Care Medicine. 2002;166(1):111-117. doi:10.1164/ajrccm.166.1.at1102
2. Holland AE, Spruit MA, Troosters T, et al. An official European Respiratory Society/American Thoracic Society technical standard: field walking tests in chronic respiratory disease. European Respiratory Journal. 2014;44(6):1428-1446. doi:10.1183/09031936.00150314
3. Enright PL, Sherrill DL. Reference equations for the six-minute walk in healthy adults. American Journal of Respiratory and Critical Care Medicine. 1998;158(5 Pt 1):1384-1387. doi:10.1164/ajrccm.158.5.9710086
4. Erratum: Reference equations for the six-minute walk in healthy adults. American Journal of Respiratory and Critical Care Medicine. 2020;201(3):393. doi:10.1164/rccm.v201erratum1
5. Troosters T, Gosselink R, Decramer M. Six minute walking distance in healthy elderly subjects. European Respiratory Journal. 1999;14(2):270-274. doi:10.1034/j.1399-3003.1999.14b06.x
6. Ramanathan RP, Chandrasekaran B. Reference equations for 6-min walk test in healthy Indian subjects (25-80 years). Lung India. 2014;31(1):35-38. doi:10.4103/0970-2113.125892

This tool compares a six-minute walk distance with published reference equations for education. It is not a medical assessment.