Introduction Low-performance populations have reduced life expectancy and elevated cardiovascular risk [16]. Among these populations, end- stage renal disease patients are characterized by high cardiovas- cular mortality [5], especially when sedentary [17]. The number and function of endothelial progenitor cells (EPCs) are correlated to the risk factors for coronary artery disease and to the Framingham score [8, 28] and independently predict future cardiovascular events [24]. EPCs could also play a role in the pro- gression of cardiovascular disease in patients with chronic renal failure, who usually show a reduced number of these cells [4]. Abstract Mobilization of circulating endothelial progenitor cells (EPCs) is increased after acute exercise and training. This study aims to evaluate whether, in a low performance population, EPC levels may be related to exercise capacity in steady state conditions. Study population consisted of sixteen hemodialysis patients. The distance walked in the 6-minute walking test (6 MWD) and the maximal speed attained in an incremental treadmill test were used to assess the exercise capacity. Physical functioning was measured by the scale on the SF36 questionnaire. Quantifi- cation of peripheral blood CD34(+) cells and enumeration of EPCs, assessed as CD34(+) cells coexpressing AC 133 and vascular endothelial growth factor receptor-2, were performed. Hemoglo- bin concentration, white blood cells, high-sensitivity C-reactive protein, total cholesterol, and triglycerides were measured. Sta- tistical analysis examined the relationship between blood pro- genitors cells versus performance parameters, laboratory param- eters, age, body mass index, hemodialysis duration, and erythro- poietin therapy. Univariate analysis revealed a significant associ- ation between percentage values of EPC and performance parameters only: 6 MWD (r = 0.720; p = 0.0017), maximal tread- mill speed (r = 0.721; p= 0.0016), and physical functioning score (r = 0.506; p = 0.0453). A similar statistical association between EPC absolute values and performance parameters was found. No correlation between CD34 + and any parameter under study was observed. Multivariate analysis indicated 6 MWD as the most significant independent factor associated with EPC level. EPC percentage value was significantly lower (p = 0.0087) in the worse (6 MWD < 300 m, n = 8) than in the better performing group (6 MWD > 300 m, n = 8). In a group of renal patients, mobi- lization of EPCs was related to the degree of exercise capacity, suggesting a possible connection with the cardiovascular risk in low performance populations limited by chronic diseases. Key words Cardiovascular risk · kidney failure · chronic · stem cells · tests Physiology & Biochemistry 368 Affiliation 1 Center for Biomedical Studies Applied to Sport, Vascular Diseases Center, University of Ferrara, Italy 2 Section of Hematology, University of Ferrara, Italy 3 Department of Nephrology, St. Anna Hospital, Ferrara, Italy 4 Section of Internal Medicine, Gerontology and Geriatrics, Vascular Diseases Center, University of Ferrara, Italy 5 Section of General Surgery, Vascular Diseases Center, University of Ferrara, Italy Correspondence Fabio Manfredini, MD · Department of Biochemistry and Molecular Biology · Section: Biochemistry of Exercise – Center for Biomedical Studies Applied to Sport · University of Ferrara · Via Gramicia 35 · 44100 Ferrara · Italy · Phone: + 39 05 32 29 10 70-2910 75 · Fax: + 39 05 32 70 5018 · E-mail: mdf@unife.it Accepted after revision: May 20, 2006 Bibliography Int J Sports Med 2007; 28: 368–373 © Georg Thieme Verlag KG · Stuttgart · New York · DOI 10.1055/s-2006-924363 · Published online October 6, 2006 · ISSN 0172-4622 F. Manfredini 1 G. M. Rigolin 2 A. M. Malagoni 1 S. Soffritti 3 B. Boari 4 F. Conconi 1 G. L. Castoldi 2 L. Catizone 3 P. Zamboni 5 R. Manfredini 4 Exercise Capacity and Circulating Endothelial Progenitor Cells in Hemodialysis Patients