The relationship between exercise tolerance and other outcomes in COPD.

Exercise training has been shown to be a clinically effective therapeutic intervention for COPD patients resulting in a myriad of beneficial effects. These include improvements in exercise tolerance, health-related quality of life and activity levels. Activity levels can be assessed using health-related quality of life instruments or instruments designed especially for this purpose. Previous studies show that the relationships between activities of daily living, assessed using generic health-related quality of life instruments, and exercise vary considerably with correlations ranging from 0.18-0.72. The relationships between activities of daily living, assessed using disease specific health-related quality of life instruments, and exercise also vary considerably with correlations ranging from 0.14-0.59. The relationships between activities of daily living, assessed using activities of daily living instruments, and exercise are less variable and generally stronger with correlations ranging from 0.34-0.83. Relationships between generic health-related quality of life instruments and exercise vary considerably (0.19-0.65) as do relationships between disease specific health-related quality of life instruments and exercise (0.18-0.61). The correlations between changes in activities of daily living and changes in exercise following pulmonary rehabilitation are generally weak (0.13-0.28). The correlations between changes in health-related quality of life and changes in exercise following pulmonary rehabilitation are also generally weak. The fact that these outcomes are not tightly associated is due, in part, to the variability in responses to the instruments used and the fact that the various instruments were often designed to assess different constructs.