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Blood rheology is one of the determinants of blood flow which becomes important when vasomotor reserve is limited or exhausted. It can be quantified ex vivo by measuring blood and plasma viscosity, haematocrit, red cell deformability and aggregation. To investigate the effects of regular exercise, a number of different experimental approaches were undertaken. A cross-sectional comparison of male athletes with sedentary matched controls showed that blood and plasma viscosity were lower and red cell deformability better in sportsmen. A 3-month longitudinal study of initially untrained healthy volunteers performing regular training revealed a fall of blood viscosity and an amelioration of red cell deformability. Finally a 2-month trial submitting claudicants to regular treadmill exercise showed a progressive fall in blood and plasma viscosity and a rise in red cell deformability. This suggests that an improvement in blood fluidity can be induced by regular physical exercise regardless of whether the blood rheology was normal or abnormal at baseline. The relevance of these findings could be three-fold. Firstly the "better than normal" blood rheology in athletes may contribute to enhanced blood flow in the working musculature and thus increase work output. Secondly the data supports the thesis of a link between blood rheology and atherogenesis. Thirdly regular exercise might be a way of therapeutically increasing blood flow in ischaemic vascular diseases.
E. Ernst (Fri,) studied this question.