Reference Values for a Multiple Repetition 6-Minute Walk Test in Healthy Adults Older Than 20 Years

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Abstract
To (1) identify greatest 6-minute walk distance (6MWD) from among several repetitions (best 6MWD) in a wide age range of healthy volunteers to develop reference values for the multiple repetition 6MWD, and (2) investigate the influence of demographics, anthropometrics, and habitual exercise activity on best 6MWD. Four 6MWD were performed on the same day in a 20-meter corridor by 41 male and 38 female healthy volunteers ranging in age from 20 to 80 years. The greatest 6MWD by each subject from among four 6MWDs was the primary outcome measure. Eighty-six percent had their best 6MWD after the first walk; an average increase of 43 meters was observed from first to best 6MWD (P < 0.003). Best 6MWD averaged 698 ± 96 meters and was inversely related to age (P < 0.001), directly to height (P < 0.001), and was greater in men than women (P < 0.0002). A regression model accounted for 41% of between-subject variability in best 6MWD (P < 0.00000001). In a subset of older subjects, predicted 6MWD significantly underestimated measured best 6MWD when reference values were used from another study where test familiarization was not provided, but this difference disappeared when values were used from the present and a third study where test familiarization was provided. The present study is the first to provide predicted 6MWD values performed with multiple repetitions and for subjects in the 20-40-year-old age range. Selection of appropriate predicted 6MWD values for interpretation of performance should be guided by subject age and degree of test familiarization provided.