Background: It is widely accepted that exercise alters the number and function of circulating leukocytes, and many factors are suggested to influence this phenomenon. The aim here was to compare white blood cell mobilization between sexes after acute vigorous-intensity exercise bout.

Methods: The study included healthy and physically active subjects, 10 men (aged 26 (SD 7) years) and 10 women (aged 33 (SD 8) years). Participants performed a 30-min cycling ergometer exercise at 70% VO2max. Blood samples were drawn at rest and 3 min, 1 and 2 h post-exercise. Changes in total leukocyte, neutrophil, lymphocyte, monocyte, eosinophil, and basophil count were analyzed and corrected for plasma volume change.

Results: Women had higher lymphocyte counts and lower eosinophil proportion of total leukocytes compared to men at all time points. Acute exercise significantly increased the number of total leukocytes and all leukocyte subpopulations excluding eosinophils in both women and men. The mobilization of all leukocyte subpopulations was similar in both sexes, but mobilization of total leukocytes, as a percentage change from rest, was greater in men. Increase in total leukocyte, neutrophil, and lymphocyte counts correlated positively with lactate concentration at 3-min timepoint and decrease in lymphocyte and basophil count after exercise correlated negatively with mean exercising heart rate in both sexes.

Conclusion: Our findings indicate that mobilization of total leukocytes is greater in men. The sex-difference however is small and not observed in any leukocyte subpopulations. Further, exercise intensity driven physiological perturbation has a role in immune cell mobilization.