Assessing Physical Activity and Physical Capacity in Subjects with Chronic Obstructive Pulmonary Disease

The overall aim of this thesis was to assess measurement properties of methods suitable for screening or monitoring of physical capacity and physical activity in subjects with chronic obstructive pulmonary disease (COPD), and to explore factors associated with physical activity levels. Methods: Four observational studies were conducted. Participants in studies I-III (sample sizes) (n=49, n=15, n=73) were recruited from specialist clinics, and in study IV from a population-based cohort (COPD n=470 and Non-COPD n=659). Psychometric properties of methods assessing physical capacity (study I) and physical activity (study II) were investigated in laboratory settings. Daily physical activity and clinical characteristics were assessed with objective methods (study III) and with subjective methods (study IV). Results: Physical capacity as measured by walking speed during a 30-metre walk test displayed high test-retest correlations (ICC>0.87) and small measurement error. The accuracy for step count and body positions differed between activity monitors and direct observations. In study III 92% of subjects had an activity level below what is recommended in guidelines. Forty five percent of subjects’ activity could be accounted for by clinical characteristics with lung function (22.5%), walking speed (10.1%), quadriceps strength (7.0%) and fat-free mass index (3.0%) being significant predictors. In study IV, low physical activity was significantly more prevalent in COPD subjects from GOLD grade ≥II than among Non-COPD subjects (22.4 vs. 14.6%, p = 0.016). The strongest factors associated with low activity in COPD subjects were a history of heart disease, OR (CI 95%) 2.11 (1.10-4.08) and fatigue, OR 2.33 (1.31-4.13) while obesity was the only significant factor in Non-COPD subjects, OR 2.26 (1.17-4.35). Conclusion: The 30 meter walk test and activity monitors are useful when assessing physical capacity and physical activity, respectively in patients with COPD. Impaired physical activity in severe COPD is related to low lung function, low walking speed, low muscle strength and altered body composition, whereas comorbidities and fatigue are linked to insufficient physical activity in patients with moderately severe COPD