Exercise-induced oxidative and hematological responses in adolescent female swimmers during the luteal phase.

Introduction: Physiological response to exercise in young female athletes is understudied, especially regarding how the luteal phase of the menstrual cycle influences performance in demanding sports such as swimming. Therefore, this study aimed to evaluate the post-exercise cortisol response, oxidative stress markers, and hematological parameters following a moderate-intensity exercise test in trained adolescent female swimmers. Materials and methods: Eighteen swimmers (aged 12-16 years) performed a swimming test (800m + 200m + 50m) during their rigorously verified luteal phase. Blood samples were collected before exercise, immediately after exercise, and after 3 hours of recovery. It was registered retrospectively on clinicaltrials.gov under NCT06903195 (March 17, 2025). Results: Moderate-intensity exercise significantly increased 8-isoprostane levels (100.70 (40.50-131.00) vs 145.10 (99.16-190.40), p<0.05), while cortisol and 4-hydroxynonenal levels decreased after 3 hours. Microscopic blood smear analysis showed erythrocyte anisocytosis and poikilocytosis, toxic granulation in granulocytes, and activated lymphocytes. Conclusion: The evaluation of young female swimmers during the luteal phase of their menstrual cycle revealed stable and subsequently decreasing cortisol levels, indicating that the exercise did not elicit a significant endocrine stress response. In contrast, the same protocol resulted in elevated levels of 8-isoprostanes. This latter finding demonstrates that the moderate-intensity exercise was sufficient to induce exercise-induced oxidative stress in this specific group of athletes.