Severe repetitive exercise and haematological status.

The effects of severe repetitive exercise on certain haematological measurements were studied. Decreases in haematocrit and haemoglobin (13% in one group of participants) took place during the first 2 weeks but not the third week of increasingly severe exertion and the reasons for this are discussed. Haemolysis probably plays only a small part and plasma volume expansion is likely to be the main cause of this phenomenon. It is suggested that there is no stimulus for the haemoglobin concentration to be increased to match the increased plasma volume as tissue oxygen tension is maintained satisfactorily.