Validity and reliability of the 6-minute walk test in a cardiac rehabilitation population

Abstract

Purpose: Although the 6-minute walk test is commonly used to assess the functional status of patients with severe cardiopulmonary disease, few studies have tested its value in a cardiac rehabilitation (CR) population with milder disease status. The purpose of this study was to examine the validity and reliability of the 6-minute walk in a Phase II/III CR program.

Methods: Ninety-four patients (61 men, 33 women) aged 63 +/- 10 years completed three 6-minute walks on nonconsecutive days. Patients also completed the Duke Activity Status Index (DASI) and the Short Form 36 Health Survey (SF-36). In addition, maximum metabolic equivalents (METs) from a symptom-limited graded exercise test were obtained from files.

Results: The 6-minute walk was linearly related to maximum METs (r = 0.687, P < 0.001), supporting the validity of the test. Patients walked significantly farther in each 6-minute walk (F = 19.83, P < 0.001), and strong test-retest reliability was demonstrated (intraclass correlation = 0.97). Distance walked decreased with older age (F = 19.49, P < 0.001), with men walking farther than women (F = 7.19, P < 0.01). The 6-minute walk was moderately correlated with scores from the DASI (r = 0.502, P < 0.001), and the Physical Function subscale of the SF-36 (r = 0.624, P < 0.001).

Conclusions: The 6-minute walk is a valid and reliable method of assessing functional ability in a Phase II/III CR population. A learning effect of 6% was observed over the three walks; however, it is unknown if this learning effect will be retained over time. This test may be particularly valuable to smaller CR centers that want to document functional improvements but do not have access to conventional treadmill tests.