INTRODUCTION: Previous investigations suggest that training intensity and duration can affect the hematology of athletes. As differences exist between distance and sprint swimmers in regards to training methods and metabolic demands, the purpose of this study was to determine whether or not there were differences in red blood cell indices when comparing elite female distance and sprint swimmers. METHODS: Twenty-two elite female swimmers were classified into two groups: a distance group (Dis) (n=11) whose primary events were 400m or 800m and a sprint group (Spt) (n=11) whose primary events were 100m or 200m. All swimmers were trained at the same facility. Red blood cell count (RBC), hematocrit (HCT), hemoglobin (HGB), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC) and red blood cell volume distribution width (RDW), were measured weekly, every Monday morning, before the first training session over a one-year period from August, 2007 until July, 2008. Due to the objective limits (such as subjects unavailable or technical error of instruments), the number of samples obtained was 477 in Dis and 459 in Spt. RESULTS: Compared to Spt, Dis had higher values of HCT (0.40¡À0.04L/L vs. 0.38¡À0.03L/L), HGB (132.41¡À10.10L/L vs. 128.66¡À9.31L/L), MCV (87.70¡À5.66 fl vs. 84.75¡À6.20fl), and MCH (29.06¡À1.35pg vs. 28.54¡À1.88pg)(P<0.05), but lower val ues of MCHC (331.97¡À15.31g/L vs. 338.19¡À17.06g/L) and RDW (13.67¡À0.94% vs. 14.25¡À0.97%)(P<0.05). No differences in RBC between Dis and Spt (4.57¡À0.34¡Á1012/L vs. 4.52¡À0.41¡Á1012/L) (P>0.05) were observed. DISCUSSION: RBC values in both groups were at an advantageous level for oxygen transportation in blood. Higher values of HCT, HGB and MCH in Dis indicate a potential for greater oxygen flow to meet the presumably greater use of oxygen in active skeletal muscles during distance swimming. Higher values of MCV in Dis were indicative of a larger proportion of young red blood cells, which had more deformability for red blood cells to pass through capillaries. Higher value of MCHC demonstrated that a larger proportion of red blood cells in Spt were aging and atrophic. Besides, atrophy varied the shapes of red blood cells; as a result, Spt had a higher value of RDW.
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