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Athlete’s Bio-Passport: Fluctuations in Reticulocyte %

November 12, 2013

In a previous blog I showed some excerpts of a large study of professional racers doing the GiroBio (a 10-day UCI under 23 stage race), highlighting trends in Hemoglobin and Hematocrit, noting that Hg tended to drop over the first 5-7 days of the race, but then trended up at the end of the 10 day period in an overwhelming majority of the athletes sampled.  Though trending upwards at 10 days, the final levels of Hg at the end of those two races were generally slightly lower than at the beginning of the race, though a portion of the athletes ended the race at a higher Hg than they had begun.  I had gotten questions about whether or not Reticulocyte percentage (R%) behaved in a similar fashion.  Below is the R% graph for that study, along with some thoughts on what the data may or may not mean.

Increases in Reticulocyte Percentage During a 10-day Stage Race
The graph in Figure 1 shows that for both editions of the GiroBio, the initial response was suppression of R% in the population as a whole after 3-4 days, increases in R% by the end of 10 days, with a significant portion of the sampled population experiencing a net increase in R% over baseline by the end of the 10 day race, indicating that red blood cell production was stimulated in most of the athletes during the latter 5 days of the race.  While this trend is quite similar to that seen in the Hg charts, it differs in that in this case the mean value of the population as a whole showed a net increase in R% from the beginning to the end of the race.  Whether this stimulation of RBC production was caused by fair or foul means is unclear – that is, is the body naturally over-compensating to the load it is subjected to, or the did the majority of the athletes sampled use of EPO or some other erythropoesis inducing chemical?


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