The six-minute walk test is a simple, inexpensive, and reproducible method for the assessment of exercise capacity. Implementation of the test does not require any advanced equipment or training for technicians. During the test, the patient walks the longest possible distance within the time of 6 minutes on the flat surface and can stop or slow down at any time and then resume walking during the test. The main result of the six-minute walk test (6MWT) is the distance covered by the patient in 6 minutes. The 6MWT shows good correlation with the peak VO2 from cardiopulmonary exercise test and is much easier to perform, and it reflects well the daily activities of the patients. However, many variables may influence this test, and, therefore, it should always be performed according to the strict given protocol. The 6MWT was proposed for the first time by Balke in 1963, and since the mid-1980s, it has been used more and more widely in different clinical conditions. This test is most commonly used in pulmonary diseases, but it has been successfully implemented also in patients with cardiovascular diseases, pre- and postsurgical treatment, different neurological disorders, and fibromyalgia or spinal muscular atrophy. However, it seems that the 6MWT is not so popular among cardiologists and cardiosurgeons as it should be.
Exercise capacity and tolerance are the most important factors in assessment of the clinical condition and prognosis of patients with cardiovascular and pulmonary diseases. Exercise capacity is the strong prognostic factor in heart failure patients and can be best described by cardiopulmonary exercise testing (CPET), mainly measuring the peak oxygen consumption. Unfortunately, such test requires complicated and expensive equipment, qualified technicians, experienced physicians, and frequent gas and volume calibration. All that makes CPET a complicated method reserved for specialized facilities.
Several different walk tests have been described in effort to measure the functional capacity, including 2-minute walk test (2MWT), 6MWT, 12MWT, self-paced walk test, shuttle walk test, and 1-mile track walk. All these tests are inexpensive and relatively simple to perform. Among them, the 6MWT seems to be the most frequently used for clinical and research purposes. This test was proposed for the first time in cardiology by Balke [
The 6MWT does not measure the peak oxygen uptake or determine the cause of dyspnea on exertion, but it correlates well (
Anyway, the 6MWT distance correlates better with the quality of life indices than with VO2 peak, and this demonstrates the 6MWT better suitability for assessing patients' ability in performing their daily activities than the CPX test [
In fact, there are many protocols of the 6MWT but the differences between them are usually small, but the most detailed and widely implemented protocol was published by the American Thoracic Society in 2002 [
The assessment of exercise capacity by means of the 6MWT is most frequently used in pulmonary and cardiac diseases. This test measures the distance a person can quickly walk on a flat, hard surface in the time of 6 minutes (the 6MWD). The 6MWT requires a 30-meter (100 ft) corridor, stopwatch, mechanical lap counter, two small cones to mark the turnover points, one chair that can be easily moved along the walking course to support the patient, worksheets on a clipboard, an available source of oxygen, a sphygmomanometer or other validated blood pressure measuring devices, a telephone, and a defibrillator. The length of the hallway should be marked every 3 meters with a cone, and the starting line should be marked on the floor using brightly colored tape. In case of repeating the test, it is important that it should be performed at the same time of the day and without any “warmup.” The patient should rest seated on a chair located near the starting line for at least 10 minutes before the test starts. Meanwhile, the contraindications for the test should be checked and identified; the pulse and blood pressure should be measured. Performing pulse oximetry is optional. The baseline and overall fatigue should be assessed using the Borg scale [
The normative data of the 6MWTD are based on several studies performed on healthy populations, and their results serve as a reference point for better understanding and proper interpretation of the 6MWT results. The 6MWT distance depends on anthropometric variables like age, gender, and weight. It also depends on the protocol specifications, mainly on verbal encouragement for the patient to continue the test and also on the results obtained by the patient in learning how to perform the test [
In the study of Gibbons et al. [
Among other studies of more elderly people, Troosters et al. [
Steffen et al. reported a mean 6MWT distance of 505 meters for men and of 467 meters for women aged 74.1 on average [
Another study performed by Enrichi and Sherrill [
Several studies have reported that the 6MWT is a reliable measure of increased mortality among cardiac patients, with the distance of less than 300 meters being a strong indicator of poor prognosis [
In patients with heart failure, a low 6-minute walk distance has been associated with increased total mortality and more hospital admissions for heart failure [
The 6MWT is a safe and simple clinical method; that is, it strongly and independently allows us to predict heart failure hospitalization rates and mortality in patients with left ventricular dysfunction. The mortality was 3.5 times higher in subjects covering less than 350 meters in the 6MWT than in those who walked over 450 meters in the Studies of Left Ventricular Dysfunction (SOLVD) registry substudy [
The 6MWT can differentiate the most severe heart failure patients from the ones with mild to moderate diseases. The 6MWD is inversely related to New York Heart Association (NYHA) functional class and quality of life (QoL). However, only the physical functioning sections of health-related quality of life questionnaires, like SF-36 or MLHFQ, correlate significantly with the 6MWT distance [
Peak VO2 is a strong indicator of heart failure severity and is an important factor in timing of heart transplantation, and the 6MWT distance is strongly correlated with peak VO2 in HF patients with reported correlation coefficient in the range from
However, others have not confirmed this relationship, and they suggest that VO2 peak is a better predictor of survival, particularly over longer followup periods [
Some authors suggest that a submaximal exercise test could reflect the results obtained from a maximal exercise test in people whose physical functional capacity is severely impaired. However, maximal exercise testing may be more precise in those with severe heart failure who are referred for heart transplantation [
There are somehow conflicting results on using the 6MW distance as a marker of improvement following medical therapy for heart failure. In some cases, treatment with betablockers, angiotensin II blockers, or ACE inhibiters in general did not increase the 6MW distance despite the increase in LVEF and NYHA functional class [
An analysis by Olsson et al. [
The test seems to be also safe in patients with refractory heart failure during the preoperative period for heart transplant surgery [
Absolute contraindications for the test include a history of unstable angina or a heart attack during the previous month. Relative contraindications are resting tachycardia HR > 120 beats/min or uncontrolled arterial hypertension [
The test strongly and independently predicts morbidity and mortality in patients with heart failure, and it is more sensitive to deterioration than to improvement in heart failure symptoms [
Another field of application of walk test is postsurgical cardiac and pulmonary rehabilitation. In the literature, we can find reference values of the 6MWT in patients early after cardiac surgery [
Slow walking speed is a component of frailty and is associated with poor muscle strength and reduced mobility. In recent studies, frailty was a significant independent predictor of mortality or need for institutional care after cardiac surgery [
The relation between the six-minute walk distance and adverse events after CABG has not been evaluated. The predictive power of the six-minute walk distance for death in heart failure patients undergoing cardiac surgery was not assessed as well. The question: “is change in the six-minute walk distance during follow-up visits associated with prognosis in heart failure patients?” also remains unanswered.