Changes in blood volume contribute to improvement in oxygen utilization (VO2max) with chronic endurance exercise training. Although hematological changes resulting from long-term endurance training have been well documented, it has not been well established whether an increased volume of endurance training preferentially affects plasma volume or red blood cell volume. To answer this question, I studied seven female and four male recreational cyclists before and after exposure to drastic increases (632%) in training volume. Following the 10-week training period, the mean hematocrit (Hct) of the 11 subjects who completed the study significantly (p0.05) correlated with the change in self-reported weekly mileage (R = 0.13 and 0.16, respectively). Based on these findings, it appears that red blood cell volume expansion is a more significant contributor to improvement in VO2max.



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