Erythrocyte Changes during Training in High School Women Cross-Country Runners

Abstract

Indices of red blood cell (RBC) status were assessed in eight high school women cross-country runners (experimental group) six times during a competitive season (Weeks 0, 1, 2, 4, 6, and 8) and three times (Weeks 0, 1, and 3) in 11 high school women who were not runners (comparison group). The only significant preseason hematological difference between the groups was a higher RBC fragility for the runners. All blood indices for both groups were within normal ranges throughout the study. During the competitive season (Weeks 0–8), the runners had a significant increase in [Vdot]O₂ max (ml/kg · min⁻¹) of 7.6% and a significant decrease in post step-test heart rate (13.4%) but showed no changes in body weight, height, or percent body fat. At Week 3, the comparison group showed an increase (0.9%) in body weight, but no changes were observed in the other anthropometric variables or post step-test heart rate. During the competitive season, the runners had significant changes in all blood variables except reticulocyte count; these changes were most marked during the first week of the season when there were significant decreases in hemoglobin (Hb) concentration (8.0%), hematocrit (Hct) (7.7%), RBC count (6.8%), and osmotic fragility (21.5% and 42.0% in 5.95 and 6.80 mM NaCl solutions, respectively) and a significant increase in mean RBC volume (1.8%). In contrast, the only significant change in blood indices of the comparison group was a decrease (1.9%) in mean RBC volume at the end of Week 1. Changes in blood variables of the runners appeared to be transient, in that values at Week 8 were comparable to those at preseason except for mean RBC volume. Although blood volume changes could be responsible for some of the blood variable changes in the runners, the results support increased RBC destruction rather than hemodilution as a cause of the RBC changes in the runners, and suggest a possible stress on body iron reserves for increased erythropoiesis during recovery from those changes.

Key Words:

• sports anemia
• red blood cells
• aerobic training effects
• hematocrit
• hemoglobin
• hematological status
• women runners