Reliability and intensity of the six-minute walk test in healthy elderly subjects

Purpose: The 6-min walk test (6-MWT) is an easy and validated field test, generally used in patients to assess their physical capacity. We think that the 6-MWT could also be conducted in the same perspective in healthy subjects, aged 60-70 yr. However, little is known about the effect of the familiarization on the 6-MWT performance and the relative intensity of this test. The aims of this study were therefore to bring precision to the 6-MWT reliability and intensity in this population. Methods: Over 3 d, 12 subjects performed two maximal exercise tests on treadmill and five 6-MWT (two in the morning and three in the afternoon) with a portable metabolic measurement system (Cosmed K4, Rome, Italy). The distance, walking speed, oxygen uptake (VO2), and heart rate (HR) values were measured during the 6-MWT. Results: Distance, walking speed, and VO2 were only lower during the first two 6-MWT (respectively, P < 0.001, P < 0.001, and P < 0.05). HR was reliable from the first 6-MWT and was higher during the tests performed in the afternoon (P < 0.001). The intensity of the 6-MWT corresponded to 79.6 +/- 4.5% of the VO2max, 85.8 +/- 2.5% of the HRmax, and 78.0 +/- 6.3% of the HRreserve. Moreover, it was higher than the ventilatory threshold in each subject (P < 0.01). Conclusion: In healthy elderly subjects, the 6-MWT represents a submaximal exercise, but at almost 80% of the VO2max. To be exploitable, two familiarization attempts are required to limit the learning effect. Finally, the 6-MWT time of day must be taken into account when assessing HR.