Hemorrheology of marathon running.

The hemorheological effects of severe exertion were evaluated in eight males and six females before and after a marathon. A highly significant fall in red cell filterability (RCF) was accompanied by a significant rise in plasma osmolality. This correlation was further studied by a series of in vitro experiments to establish a cause-effect relationship. As plasma osmolality increased, RCF progressively diminished. These observations demonstrate that plasma hyperosmolality is an important etiological factor in reducing RCF during strenuous exercise.