Reticulocytes in athletes: Longitudinal aspects and the influence of long- and short-term exercise.

Reticulocytes (Ret) are a key variable in the emerging concept of the athlete's biological passport and the longitudinal monitoring of biological parameters in the field of anti-doping. In this context, knowledge on the variability of Ret in athletes and the influence of exercise is necessary. The aim of the present study was to evaluate longitudinal variation in Ret and the influence of short- and long-term exercise.Ret% in 793 samples of 238 athletes were determined and analyzed in different study parts for inter- and intra-individual variation and the impact of long- (competitive season) and short-term (all out) exercise.Median Ret% was 0.9 (CI(0.5-99.5%) 0.4-2.7). Intra-individual variation for Ret% was 0.0118; inter-individual variation 0.0124. During periods of intensive exercise Ret% was slightly lower (mean - 0.1%, p = 0.048). After a short, all-out exercise bout, Ret% was increased (+0.5%, p = 0.0028).Athletes mostly display similar Ret% than the normal population; however, intra-individual variation in athletes is higher. During the competitive season of endurance athletes, Ret% is slightly decreased. After short bouts of intense exercise Ret% is increased. These data can be used for the interpretation of blood profiles in athletes.