Objective: Patients with systemic lupus erythematosus (SLE) have poor physical fitness as measured by maximal oxygen uptake (VO(2max)), which is associated with disability and fatigue. The purpose of this study was to validate, in this population, the Siconolfi Step Test (SST) developed to predict VO(2max) in healthy individuals.
Methods: Thirty patients with well-controlled SLE were tested on a cycle ergometer until volitional exhaustion, and 25 women and 4 men (mean +/- SD age 48 +/- 14 years, weight 71.5 +/- 13.7 kg) fulfilled the criteria for maximal effort. VO(2max) measured during this incremental test was compared with VO(2max) predicted by the SST using Bland and Altman 95% limits of agreement (LOA) and intraclass correlation coefficient (ICC). The SST was repeated twice to assess its reliability.
Results: The ICC between predicted and measured VO(2max) (mean +/- SD 1.67 +/- 0.41 liters/minute versus 1.57 +/- 0.39 liters/minute) was moderately high (0.73, P < 0.001). Bland and Altman analysis revealed a trend for a positive bias (P = 0.083) and 95% LOA of +/-0.58 liters/minute. There was a very high ICC (0.97, P < 0.001) between VO(2max) predicted by the first and second SST (mean +/- SD 1.66 +/- 0.40 liters/minute versus 1.67 +/- 0.41 liters/minute), and no significant bias (P = 0.500). The 95% LOA were +/-0.20 liters/minute.
Conclusion: The results demonstrate that the SST is well tolerated, reasonably valid, and highly reliable in patients with well-controlled SLE. Therefore, this simple, submaximal exercise test might be useful for assessing physical fitness in clinical practice and epidemiologic studies.