Changes in red cell density and related indices in response to distance running

Summary

The red cell population in peripheral venous blood was characterised in 7 young males before and up to 16 days after a 21.1 km road race.

There was a 1.9±2.4% (mean±SD) reduction in plasma volume immediately post race (p<0.05), an increase in serum osmolality from 277±4 mOsm·kg⁻¹ to 291±14 mOsm·kg⁻¹ (p<0.05) and a reduction in red cell water (64.4±0.3% to 63.4±0.4%,p<0.001). The latter was consistent with alterations in the manually derived MCV and MCHC values although the same Coulter derived values were unaltered. A concomitant increase in median red cell density in whole blood (1.1045±0.0009 g·ml⁻¹ pre race to 1.1057±0.012 g·ml⁻¹ immediate post race,p<0.05) was recorded by centrifugation through phthalate esters of different density. The changes in creatine content of the red cells suggested that during the race younger cells were released into the circulation but that 24 h to 72 h after the race the mean red cell age had increased. Similarly, fractionation of the red cells on discontinuous Percoll density gradients indicated that the cell population was significantly denser in all post race samples up to 72 h but had normalized by a 16 day sample; the osmotic fragility was similarly affected. The reticulocyte count did not significantly increase throughout the experiment but the mean red cell creatine content was elevated 16 days post exercise compared with the pre-race value suggesting a possible increase in erythropoiesis between 72 h and 16 days post race. The study shows that exercise of this type may induce a small reduction in mean red cell survival time but that this does not immediately change erythropoietic activity.