Diurnal variation in red blood cell variables in athletes after single and repeated bouts of exercise.

Background: The aim of this study was to examine the diurnal and exercise-related changes in red blood cell variables which serve as indirect markers of doping in sports.

Methods: Ten men and 7 women, all undoped highly trained endurance athletes aged 19-34 years, were included in the study. Before and on the day with single and repeated bouts of exercise, blood samples were collected at 07:00, 09:00, 13:00, 18:00, and 21:00, at least 2 hours after exercise.