Effect of acute aerobic exercise in different times of day on iron status and hematological factors in professional football players

Background and aims: Exercise time is one of the main challenges of athletes. The purpose of this study was to investigate the effect of acute aerobic exercise at different times of the day on iron status and hematological factors in professional football players. Methods: In this quasi-experimental study, 40 professional football players were randomly divided into morning exercise, evening exercise, morning control, and evening control groups. The experimental groups performed Bruce’s test in the morning and evening. To measure iron, ferritin, red blood cell (RBC), and hemoglobin (Hb), the blood samples were taken before, immediately after, as well as 24 and 72 hours after the Bruce test. Repeated-measure ANOVA and two-way ANOVA (group*time) were used to analyze the obtained data. Results: The results showed a significant increase immediately after an acute aerobic exercise while demonstrating a significant decrease in RBC and Hb in morning and evening exercise groups 24 and 72 hours after the exercise compared to the control groups. In addition, a significant reduction immediately after the acute aerobic exercise, whereas a significant increase 24 and 72 hours after the exercise, was observed in the serum levels of iron and ferritin in the morning and evening exercise groups compared to the control groups. As regards the serum levels of iron, an immediate significant decrease, along with a significant increase 24 hours after the acute aerobic exercise was found between the morning and evening exercise groups (P≤0.05). Conclusion: It seems that performing acute endurance training in the evening is safe in terms of reducing the serum levels of iron and developing the "exercise-induced anemia". Finally, at least 24 hours is required for the recovery of hematological parameters after acute endurance training.