Reference equations for the 6-minute walk distance in healthy Portuguese subjects 18-70 years old

Six-minute walk test (6MWT) is used for evaluating functional exercise capacity. To the best of our knowledge, there are no reference equations to predict six-minute walk distance (6MWD) for the Portuguese population. The aims of the present study were to measure anthropometric data and 6MWD in a sample of healthy Portuguese population, to establish reference equations to predict 6MWD and to compare our equations with those obtained by previously published studies.

We conducted an observational prospective study. We consecutively recruited 158 healthy 18-70 years old subjects from Porto district, who performed two 6MWTs using a standardized protocol. The best 6MWD was used for further analysis.

The mean 6MWD was 627.8m (SD=73.3m). The variables that were significantly associated with the 6MWD were age, sex, BMI and ΔHR (Heart Rate_{at the end of the test}-HR_{at rest)}. We found three explanatory models for 6MWD, the best with an explanatory power of 38%: 6MWD=721.7-1.6×Age-4.0×BMI+0.9×ΔHR+58.4×Sex. We verified that 6MWD decreased 1.6m per year of age, and 4.0m per unit of BMI and increased 0.892m per beat per minute. Moreover, on average, males walk 58.4m more than females (p<0.001). Applying equations from other studies to our population resulted in an overestimation or underestimation of the 6MWD.

The present study was the first to describe the 6MWD in healthy Portuguese people aged 18-70 years old and to propose predictive equations. These can contribute to improving the evaluation of Caucasian Mediterranean patients with diseases that affect their functional capacity.