Six-minute walk distance in healthy Singaporean adults cannot be predicted using reference equations derived from Caucasian populations

Objectives: The 6-min walk test (6MWT) is commonly used to assess the functional exercise capacity of individuals with cardiopulmonary disease. Recent studies have established regression equations to predict the 6-min walk distance (6MWD) in healthy Caucasian populations; however, regression equations have yet to be established for the Singaporean population. The aim of this study was to determine 6MWD in healthy Singaporeans and identify contributors to 6MWD in this population. We also compared measured 6MWD with predicted 6MWD from two regression equations derived in Caucasian subjects. Methodology: Thirty-five healthy subjects (32 Chinese, 16 men) aged between 45 and 85 years performed three walking tests using a standardized protocol. 6MWD was defined as the greatest distance achieved from the three tests. Heart rate (HR) was recorded each minute during the 6MWT. Other measurements included age, height, leg length, smoking history and self-reported physical activity. Results: 6MWD was 560 +/- 105 m and was not significantly different between men and women (P = 0.19). 6MWD was related to age (r = -0.36, P = 0.03), height (r = 0.35, P = 0.04), leg length (r = 0.38, P = 0.02) and the maximum HR achieved on the 6MWT when expressed as a percentage of the predicted maximum HR (%predHRmax, r = 0.73, P < 0.001). Stepwise multiple regression analysis showed that age, height, weight and %predHRmax were independent contributors (P < 0.01) to 6MWD, explaining 78% of the variance. Predicted 6MWD using regression equations derived from Caucasian subjects exceeded measured 6MWD by more than 75 m (P < 0.001). Conclusions: This is the first study to report 6MWD for healthy Singaporeans aged 45-85 years. The regression equation developed in this study explained 78% of the variance in 6MWD. Published equations derived from Caucasian subjects overestimate 6MWD in Singaporean Chinese.