Purpose. Exercise tests represent an important clinical tool to evaluate cardio-respiratory fitness and to predict future adverse cardiovascular events. However, use of such tests in patients with rheumatoid arthritis (RA) is relatively uncommon despite well-established evidence that low exercise capacity and high CVD mortality are features of this disease. Therefore, this study examined the validity and reliability of a sub-maximal step test for use in RA patients. Methods. Thirty patients (24 females) (mean？±？SD age years) performed a sub-maximal step test on two occasions to estimate the criterion measure of cardio-respiratory fitness ( ). A further maximal cycling test provided a direct fitness measurement ( ). Pearson correlation coefficient, intraclass correlation coefficient (ICC), Bland and Altman plots, and 95% limits of agreement (LOA) were used to determine the validity and reliability of the sub-maximal test. Results. Estimated correlated well with directly measured ( , LoA ±5.7？mL·kg？1·min？1). Test-retest reproducibility for estimated was excellent ( , LoA ±2.2？mL·kg？1·min？1). Conclusion. The sub-maximal step test studied here represents a valid and reproducible method to estimate cardio-respiratory fitness in RA patients. This test may be useful for the assessment and management of CVD risk in a clinical setting. 1. Introduction Physical fitness reflects the overall ability to perform activities of daily living [1]. Data from numerous epidemiological studies indicate that low cardio-respiratory fitness is a strong independent risk factor for all-cause and cardiovascular disease (CVD) mortality in asymptomatic individuals, persons with comorbid conditions (hypertension, obesity, and type 2 diabetes mellitus), and those with established coronary artery disease [2]. It is reported that the strength of association between low cardio-respiratory fitness and mortality is comparable to that between mortality and traditional CVD risk factors such as obesity, hypertension, hypercholesterolemia, and smoking [3–5]. This association is very important, especially for clinical populations known to have an exacerbated CVD risk. One such population is patients with rheumatoid arthritis (RA). It has been shown that CVD accounts for up to 50% of deaths in RA [6], and, typically, CVD events occur earlier, and to a greater extent in this population relative to age-matched healthy controls, and sometimes even before the fulfilment of all criteria of RA [7]. It is hypothesised that inflammation is the major contributor to CVD in RA [7] with other traditional
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