To assess reliability and validity of a single stage submaximal treadmill test to estimate aerobic capacity in women with rheumatic disease.
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.
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.
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.