The Six Minute Walk Test… Why Six Minutes

6 minutes on a stopwatchChances are you have been through a six minute walk test either at the hospital, pulmonary rehab center or doctor’s office. Our friend John Goodman BS, RRT, answers the question, ‘Why Six Minutes?’

A Little Background

The Six Minute Walk Test (6MWT) is a time-distance walk, first introduced by Balke in 1963. Balke developed this test as a straightforward and objective measure of functional capacity. The test could not be any simpler to perform as it only requires you to walk as far as possible in a set period of time. The distance is usually reported as 6 Minute Walk Distance or 6MWD.

A variety of distances and times have been investigated since the 1960s: 2 minute, 6 minutes and 12 minute walks. The health status of some participants was so poor that they were simply unable to complete the 12 minutes of physical activity.

Research has shown that 40% of active adults over the age of 75 have difficulty walking just a quarter mile. As it turned out, 2 minutes simply wasn’t long enough, and there didn’t seem to be any further benefit gained in walking 12 minutes so the 6MWT, as we know it today, came into existence. The 6MWT has proven to be a very reliable and reproducible test and clinicians place a great deal of confidence in the test results. Both cardiac and pulmonary rehabilitation programs use the 6MWT to measure physical fitness, or in some cases, even act a predictive tool for morbidity or mortality.

Guidelines Developed

In an attempt to standardize the testing protocol for all patients, the American Thoracic Society came up with a set of guidelines. You wear comfortable clothes with appropriate footwear and may use a cane or walker. It is not a bad idea to have a light meal one to two hours before the test. Patients normally rest for 10 minutes or so prior to the test, after which time some baseline vital signs will be recorded. This includes a baseline oxygen saturation reading as well as blood pressure. You will be coached while walking, but basically,

the walk itself is up to you. Directions are simple: This is more of a marathon walk for six minutes than a sprint. Walk continuously at your own pace. Various measurements will be taken. You will rate your shortness of breath using the Borg Dyspnea Scale before and after the walk.

A Few Variables

Although the 6MWT has been somewhat standardized, there are differences in testing techniques between different clinical centers and labs. In particular, there is no agreement on the length of the test course, the shape of the test course (straight, continuous circle or oval), whether a practice walk should be done before the final test, and whether the best of two or just the second of two walks should be recorded.

As was anticipated there was a “learning effect” in evidence. On average the second 6MWT showed an increase of 66 feet compared to the first walk. In subsequent studies, it became clear that a circular or continuous circle (or oval) track produced significant differences in distance walked, in fact, the average was 110 feet.

 

Shortness of Breath Modified Borg Dyspnea Scale
0 Nothing at all
0.5 Extremely slight (just noticeable)
1 Very slight
2 Slight
3 Moderate
4 Somewhat severe
5 Severe
6
7 Very severe
8
9 Extremely severe (almost maximal)
10 Maximal

 

The original use of the test that was limited to cardiac and respiratory dysfunction has been substantially widened. Clinical indications now include: pulmonary hypertension, COPD, congestive heart failure, pulmonary rehabilitation, lung resection, lung transplant, lung volume reduction surgery, interstitial lung disease, cystic fibrosis, peripheral vascular disease and fibromyalgia.

Contraindications to Testing

There are just a few contraindications to doing a 6MWT on certain people. Most of them are common sense and include: unstable heart pain, resting heart rate over 120/min, recent heart attack, inability to ambulate and poorly controlled hypertension. There are also a few other factors that may influence the distance someone can walk. They include being of short stature, being older than 75, being very tall, being a woman, and having other significant medical co-morbidities. These could include things like untreated hospital waiting roomanemia, musculoskeletal limitations, impaired mental status and interaction with tester.

One of the more important variables that need to be  considered  includes the relationship between you and the technician. To avoid having you try and follow your tester, it is recommended that the technician walk behind you as you set the pace. The technician may carry your oxygen if necessary. If the flow rate needs to be adjusted, it should be noted by the technician as well as the saturation achieved. Encouragement phrases such as “you are doing well” and “keep up the good work” may be called out at regular intervals. It is common to announce elapsed time at the halfway point, with 2 minutes remaining, and then when there is one minute remaining. Chairs are normally placed along the route to catch your breath should that be necessary.

Degree of Breathing Difficulty

When you have completed the full 6MWT, you should immediately rate the level of your breathing difficult (dyspnea) using the Borg Scale once again. Other questionnaires may be administered to rate your activities of daily living. Physical activity levels can also be assessed by simple questionnaire, as well as quality of life assessments. At this point one can see why the 6MWT is most commonly performed in a cardiac or pulmonary rehabilitation setting. All of the necessary equipment, plus enough physical space to lay out the course, the availability of trained staff and an emergency cart are all centrally located. Reports can be generated and delivered almost in real time to the referring physician. Results of the 6MWT have compared very favorably to the same tests performed on a treadmill.

Distance Norms Vary Widely

Many studies have been done over the years to give us normal values for the 6MWT. We find the actual distance walked varies widely in men from a low of 1,309 to a high of 2,553 feet (399 meters to 778 meters) with the average value being 1,890 feet (576 meters) in six minutes. For women the range was 1,017 to 2,179 feet (310 meters to 664 meters) with an average distance of 1,621 feet (494 meters) walked in six minutes.

As expected, the distance walked in six minutes goes down as we age. There is a pretty strong correlation with how well we do on the test and our own self-reported functional ability. The 6MWT has a very high index of reproducibility, takes very little staff time, and perhaps most important of all, does not require a physician to be in attendance.

All in all, we get a great deal of information from this economical, simple and safe way to check your functional status.

John R. Goodman BS RRTJohn R. Goodman BS RRT is Executive Vice President of Technical/Profes­sional Services at Transtracheal Ser­vices, Denver, CO, who says “All You Need Is Love!”

John R. Goodman BS RRT is Executive Vice President of Technical/Profes­sional Services at Transtracheal Ser­vices, Denver, CO, who says “All You Need Is Love!”

The test could not be any simpler to perform as it only requires you to walk as far as possible

in a set period of time.