6-Minute Walk Test
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The 6-minute walk test (6MWT) measures the distance (6MWD) that a person can quickly walk on a flat, hard surface in 6 min. The test is submaximal and self-paced, with rest breaks allowed as needed.
Historically, aerobic functional capacity has been evaluated by asking a person “how many flights of stairs can you climb?” or “how many blocks can you walk?” Due to poor reliability and validity of such questioning, more objective methods have been established. In 1963, Balke created a simple test of the distance a person could walk in a specified amount of time. In 1968, Cooper described a 12 min overground walking test for healthy individuals, which was adapted for patients with chronic bronchitis in 1976. The 6MWT was created to accommodate persons with respiratory disease for whom a 12 min span was excessive. The test has been adopted for use for persons with a wide range of different cardiopulmonary diseases as well as orthopedic and neuromuscular diagnostic groups.
A shorter version, the 2-minute walk test (2MWT), has also shown to correlate highly with the 6MWT and is in increasing use. The 2MWT has been included in the National Institutes of Health (NIH) Toolbox for the Assessment of Neurological and Behavioral Function (http://www.healthmeasures.net/explore-measurement-systems/nih-toolbox).
Concurrent validity of the 6MWT has been established by significant correlations with peak oxygen uptake (r = 0.56 to r = 0.88) and by better correlation with quality of life measures than peak oxygen uptake. Furthermore, intervention-related changes in 6MWD correlate with subjective improvement in dyspnea.
The 6MWT also has good test-retest reliability, with an ICC of 0.75–0.97 and a coefficient of variation of approximately 8%, which is better than that of functional status questionnaires (22–33%).
The 6MWT evaluates global aerobic exercise capacity, which is dependent on the responses of the cardiovascular and pulmonary systems, blood, neuromuscular units, and muscular metabolism. Unlike maximal cardiopulmonary exercise testing, the 6MWT cannot determine peak oxygen uptake, diagnose the cause of exertional dyspnea, or determine the mechanism of exercise limitation. It is instead designed to evaluate aerobic functional capacity for activities of daily living, which are performed at submaximal levels of exertion. The 6MWT has been used to assess baseline functional limitations, disease progression, and as an outcome measurement for a wide range of cardiopulmonary diseases. It has also been used for persons with various orthopedic and neuromuscular diagnoses, including hip fracture, stroke, and spinal cord injury.
Absolute contraindications for the test include recent unstable angina or myocardial infarction (during the previous month). Relative contraindications include resting heart rate >120 bpm, systolic blood pressure >180 mmHg, diastolic blood pressure >100 mmHg, or stable exertional angina (patients should perform the test after using their antianginal medication, and rescue nitrate medication should be readily available).
Enright and Sherill (1998) collected normative data (cross-reference) for the 6MWT on healthy adults aged 40–80 years and found a mean 6MWD of 576 m for men and 494 m for women. The following normative equations were also derived:
6MWT distance = (7.57 × height cm) − (5.02 × age) − (1.76 × weight kg) − 309 m for men
6MWT distance = (2.11 × height cm) − (2.29 × weight kg) − (5.78 × age) + 667 m for women
For an individual patient with COPD, a 6MWD improvement of 71–86 m can be interpreted as meaningful change with 95% confidence.
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