Abstract
The purpose of this study was to evaluate the rest-retest reliability and validity of a constant-load endurance exercise test on a cycle ergometer with a workload of 75% of maximal work capacity (Wmax) in patients with moderate to severe chronic obstructive pulmonary disease (COPD).
In 60 patients with COPD (FEV1 40 +/- 15% pred), exercise endurance time was measured with a constant-load endurance exercise tests at 75% of Wmax, on two different occasions. In a subgroup of 20 patients, test-retest reliability of the measurement of end-exercise ventilatory and metabolic responses was assessed. Validity of the cycle endurance test was assessed comparing endurance time and total work performed during the cycle endurance test to peak oxygen uptake ([latin capital V with dot above]O2peak) and the 12-minute walking distance (12MWD).
Test and retest assessments of cycle endurance time did not differ statistically significantly (P = .40). Highly significant intraclass correlation coefficients (ICC >= 0.85;P < .001) were found between test and retest of assessment of endurance time as well as of end-exercise ventilatory and metabolic responses. In addition, statistically significant correlation coefficients were found between [latin capital V with dot above]O2peak and endurance time (r = 0.50;P = .001) and total work performed (r = 0.72;P < .001) during the constant-load cycle test. Significant correlation coefficients of the same magnitude were found between 12MWD and endurance time (r = 0.58;P = .001) and total work performed (r = 0.72;P < .001) during the constant-load cycle test. It is concluded that constant-load exercise testing on a cycle ergometer with a workload of 75% of maximal work capacity is a reliable and valid method to assess exercise endurance in patients with COPD.
Impaired exercise ability is a common feature in patients with chronic obstructive pulmonary disease (COPD). Exercise performance in patients with COPD may be assessed by symptom-limited incremental exercise tests as well as endurance tests with submaximal workloads. These tests have the potential to produce complementary information. Maximal exercise tests usually are performed to assess the nature of the exercise impairment in patients with pulmonary diseases, 1 but appear to be relatively insensitive in measuring changes after interventions such as rehabilitation. 2 In contrast, constant-load endurance tests are highly responsive in measuring acute improvements in exercise endurance such as from breathing supplementary oxygen 3 and receiving noninvasive ventilatory support 4 as well as improvements after pulmonary rehabilitation. 5 In constant-load endurance tests, the time is measured as patients are able to keep up a constant-load work on a cycle ergometer, usually set between 60% and 75% of symptom-limited maximal exercise capacity. In addition, the end-exercise physiological responses may be used as outcome measure.
Despite the frequent use and high level of responsiveness in detecting changes in exercise performance using constant-load cycle endurance tests, the reproducibility of the assessment of endurance time and physiological responses has been poorly documented. A systematic increase in exercise performance during repeated testing in patients with COPD because of learning has been well documented using floor walk tests 6 and walk tests on a treadmill. 7 In addition, in patients with COPD random measurement error may be present during repeated assessments of exercise endurance because of a variation in the severity of airway obstruction, for instance from of the use of medication. 8 Lastly, nonphysiological factors such as motivation and fear may influence exercise performance, also contributing to variability in successive testing. 9
Validity of constant-load cycle endurance tests has never been a subject of investigation in patients with COPD. In general, insight into the validity of a measurement instrument is important because it may provide understanding of the nature of what is being measured. 10 Concurrent validity of the cycle endurance tests may be determined by comparing the outcome with other widely used and accepted measures of exercise capacity of which reliability and validity have been established, such as peak oxygen uptake ([latin capital V with dot above]O2peak) 11 and 12-minute walking distance. 6
The aim of the current study was to evaluate the test-retest reliability of the measurement of exercise endurance and end-exercise physiological responses of a constant-load exercise test on a cycle ergometer with a workload of 75% of Wmax in patients with moderate to severe COPD. Subsequently, the concurrent validity was determined by comparing outcome of the constant-load cycle test to [latin capital V with dot above]O2peak and the 12 minute walking distance (12MWD).