Reliability and clinical correlates of the Astrand–Rhyming sub-maximal exercise test in patients with schizophrenia or schizoaffective disorder

Cardiovascular fitness is reduced in people with schizophrenia and is related to an increased morbidity and mortality. There is mounting interest in the accurate measurement of cardiovascular fitness in schizophrenia, yet existing measures used in the general population have not been tested on validity and reliability in this high-risk group. Therefore, we examined the reproducibility and feasibility of the Astrand–Rhyming sub-maximal exercise test in patients with schizophrenia or schizoaffective disorder. Secondary aims were to assess minimal detectable changes, practice effects and the presence of clinical symptoms that are associated with cardio-respiratory fitness (expressed as estimated oxygen uptake). From 47 patients with schizophrenia or schizoaffective disorder two trials of the Astrand–Rhyming test, administered within three days, were analysed. The intraclass correlation coefficient for the estimated oxygen uptake between the two tests was 0.92 (95% confidence interval: 0.85–0.95). The minimal detectable change was 6.5 ml O2/min/kg. No practice effect could be detected. A backward regression analysis demonstrated that illness duration, negative symptoms and level of physical activity explained 63.0% of the variance in estimated oxygen uptake. The current study demonstrates that the Astrand–Rhyming test can be recommended for evaluating the aerobic fitness in patients with schizophrenia or schizoaffective disorder.