Haematological changes due to triathlon competition

A twelve parameter blood cell profile has been measured in 6 subjects before and after each phase of triathlon event. This involved 29 miles cycling, 12 miles running and finally 18.5 miles canoeing. There was a significant decrease in plasma volume (8.7% +/- 3.1%, p less than 0.001) following the first phase (cycling); this decrease was sustained to the end of the event. A substantial increase in the number of circulating leukocytes after cycling (84 +/- 58%) and running (255 +/- 83% of pre-event value) was observed. There was no further leucocyte increment after the canoeing stage which may indicate that the circulating concentration of these cells was maximal after running. Fluid shifts following the postural alteration accompanying the different types of exercise and subject variability may have masked any subtle changes in the red cell parameters.