Objective: To assess reliability and validity of a single stage submaximal treadmill test to estimate aerobic capacity in women with rheumatic disease.
Methods: 30 women with rheumatic disease (rheumatoid arthritis = 19; systemic lupus erythematosus = 5; mixed connective tissue disease = 2; psoriatic arthritis = 4) performed a submaximal exercise test at a self-selected walking speed between 3.2 and 7.2 km/h on 2 occasions, and one subjective maximal exercise test with respiratory gas analysis. Estimation of aerobic capacity from the submaximal test was obtained from a regression equation using age, walking speed, and exercise heart rate. Aerobic capacity from maximal testing was determined by observed peak oxygen consumption and by estimation using test duration in a regression equation. Correlation and regression analyses were performed to assess test-retest reliability and criterion validity of the submaximal method.
Results: Intraclass correlation coefficient for the submaximal test was ICC = 0.97 (95% CI = 0.94-0.99). Comparison of results from the submaximal test to the maximal test using both observation and estimation methods to determine aerobic capacity ranged from r = 0.77 to 0.80, with R2 of 0.59 to 0.65. The submaximal regression model, originally developed and validated in a sample of persons without rheumatic disease, was significantly different in this sample of women with rheumatic disease.
Conclusion: This single stage treadmill test, suitable for use in clinical and community settings, appears to be a reliable and valid method to safely assess aerobic capacity in women with rheumatic disease. There was a tendency for the submaximal method to overestimate aerobic capacity in this sample.