Changes in blood volume contribute to improvement in VO2max with chronic endurance exercise training. Although hematological changes to chronic endurance training have been well documented, it has not been well established whether an increased volume of training in trained individuals preferentially affects plasma volume vs. red cell volume. To answer this question, we studied 8 female and 3 male recreational cyclists before and after exposure to drastic increases in training volume. Following the 10-week training period, mean Hct of the 10 subjects who completed the study significantly (p\u3c0.05) increased from 42.9% to 48.45%. Mean Hb also increased significantly (p\u3c0.05) from 14.6g/dL to 16.4 g/dL. The changes in Hct and Hb were not significantly (p\u3e0.05) correlated with the change in self-reported weekly mileage (R = 0.13 and 0.16 respectively). The major finding of this study is that both Hct and Hb increase substantially following large training volume increases in recreational cyclists. Furthermore, it appears that there are preferential increases in red blood cell volume compared to plasma volume expansion in this population
