Physical functioning

Physical functioning was estimated by 6-min walking distance and level of physical activity (PA). Participants performed a 6-min walking test in which they attempted to walk as far as possible in the allotted time (Bean et al. 2003) at baseline and at the 3-year follow-up. The 6-min walking test is a performance-based measure of functional exercise capacity, and it can be used as an indicator of exercise tolerance or aerobic capacity. The test was performed on a 50-m indoor track, and participants were instructed to complete as many laps as possible within 6 min. The distance (m) covered in the 6-min walk was recorded and used in the analysis. A standardized protocol and safety guidelines issued by the American Thoracic Society (ATS Committee on Proficiency Standards for Clinical Pulmonary Function Laboratories 2002) were followed.

Physical activity was assessed using a modified version of the seven-point Grimby scale (Grimby 1986) at baseline and at the 3- and 11-year follow-ups. The categories used in questionnaire were as follows: (1) inactive, (2) light activity 1–2 times per week, (3) light activity several times per week, (4) moderate activity 1–2 times per week, (5) moderate activity several times per week, (6) high activity several times per week, and (7) competitive sports several times per week. For the analysis, categories 5 and 6 were combined, as very few participants (0 to 7) reported category 6 and none category 7.