Angus, C., Elwell, C. E., & Cooper, C. E. Can measurements of erythrocyte transit time inform on the mechanisms of increasing muscle oxygen extraction? Medicine and Science in Sports and Exercise, 35(5), Supplement abstract 522.

Changes in muscle blood flow and volume were used to indicate the time it takes red blood cells to flow through muscle. Males (N = 6) performed a single-arm incremental exercise test. Blood volume and flow increased in both the exercising and non-exercising arm. The non-exercising arm was used for analysis because it mirrored the flow dynamics of the exercising arm. Blood volume was divided by blood flow to provide an estimate of transit time.

Transit time decreased in the early stages of the exercise but increased in the latter stages. It was hypothesized that the slowing could be due to a lengthening of the capillary pathways or a decrease in red cell velocity (possibly due to exercise induced increased hematocrit).

Implication. Increased red cell transit time might have functional significance by allowing increased oxygen extraction as the blood passes through working muscle.

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