Background:
The 6-minute walk test is an inexpensive, safe and easy tool to assess functional capacity in patients with cardiopulmonary diseases including heart failure (HF). There is a lack of reference values, which are a prerequisite for the interpretation of test results in patients. We therefore assessed the association of the 6-minute walk distance (6MWD) with the non-modifiable parameters age, sex, and height in the adult general population.

Methods:
The prospective Characteristics and Course of Heart Failure Stages A-B and Determinants of Progression (STAAB) cohort study investigates a representative sample of residents of the City of Würzburg, Germany, aged 30 to 79 years, without history of HF. Participants underwent detailed clinical phenotyping as well as a strictly standardized assessment of the 6MWD using a 15m hallway. After exclusion of individuals with limited capability to properly perform the 6-minute walk test, we applied generalized linear models to determine mean (SD) of 6MWD for men and women as well as for each age decade, respectively, also considering body height.

Results:
We here report on n=2650 participants (51% women; mean age 57±11 years) with valid 6MWD. We found a non-linear relationship between age and 6MWD. A change in slope was apparent at the age of 59.7 years (95%CI 57.0-62.5; see figure, panel A). Mean 6MWD was higher in men than in women: +20 (15-25)m. When incorporating body height into the model, the mean loss in 6MWD was 1.8 (1.2-2.3) m per life year until the age of 59.7 years, and 5.3 (4.5-6.0) m per life year beyond. The 6MWD was 1.5 (1.3-1.8)m higher per +1cm in body height, and had no longer a significant independent relationship with sex (see figure, panels B/C). Residual 6MWD from non-linear regression with age and body height as predictors was also non-normal, and slightly skewed with a longer left tail.

Conclusions:
In a representative sample of the general population, the 6MWD depended on age and body height, but not on sex. Based on these results, the percent distance of predicted can be computed also for patients, thus allowing for an objective measure of physical performance.

Figure