Research group: twenty-four and homogeneous female swimmers, who train swimming intensively and attend the Sports Championship School Complex. In this cohort, baseline serum cortisol levels were considered, and the athletes were divided into two groups: 1) Serum cortisol <230 (normal): n=14 2) Serum cortisol >230 ng/ml (high): n=10

In this study, the athletes were subjected to intensive swimming tests in breaststroke crawl (800m + 200m + 50m) with 15 minutes of active rest between test sections in the water.

Blood samples took from the cubital vein at three time points: before stress test (pre-exercise), one minute after the end of the test (post-exercise), and after a 3-hour recovery period (3h recovery). Measurements morphology, 4-Hydroxynonenal (4-HNE), 8-isoprostane, cortysol levels were determined using ELISA kits.

The data of 24 trained female from the Sports Championship School Complex. All athletes presented as medically fit, with no underlying health problems. In this cohort, baseline serum cortisol levels were considered, and the athletes were divided into two groups: 1) Serum cortisol <230 (normal): n=14 2) Serum cortisol >230 ng/ml (high): n=10 In this study, the athletes were subjected to intensive swimming tests in breaststroke crawl (800m + 200m + 50m) with 15 minutes of active rest in the water. Blood samples took from the cubital vein at three time points: before stress test (pre-exercise), one minute after the end of the test (post-exercise), and after a 1-hour recovery period (3h recovery).

Measurement: All determined parameters were measured with the available equipment in the ZWKF laboratory in Gorzów Wielkopolski and using commercial assay kits. Measurements were performed by the project contractors.

1. Polyethylene tubes (2.7ml) containing dipotassium ethylenediaminetetraacetic acid (EDTAK2) anticoagulant were used for the following tests: (a) complete blood count (7 parameters) determined on the MYTHIC 18 hematology analyzer (Orphee Medical, Geneva, Switzerland). Red blood cell indices: RBC (Red Blood Cells), HGB (Hemoglobin), HCT (Hematocrit), MCV (Mean Corpuscular Volume), MCH (Mean Corpuscular Hemoglobin), MCHC (Mean Corpuscular Hemoglobin Concentration), RDW (Red Blood cells Distribution Width). (b) a manual blood smear was made by placing a drop of blood on a slide and then spreading it with a uniform motion. After drying, it was colored by the May Grunwald-Giemsa method according to the procedure. The stained and fixed smear after drying was viewed under a microscope for quantitative and qualitative assessment.
2. Polyethylene clotting activator tubes (9 ml) were centrifuged to separate the morphotic elements from the serum using a centrifuge (3000 rpm for 10 min). The serum was pipetted into several Eppendorf tubes, which then was frozen (temp. -80 °C). All the following biochemical parameters were determined from the extracted serum: (a) using the ELISA method by the test manufacturer's instructions. The designations include the flowing parameters:

4-Hydroxynonenal (4-HNE), 8-isoprostane, cortysol. (3) The lactate (La) concentration was determined from the capillary blood immediately after collection using a commercially available kit (Dr. Lange, Germany).

The athletes' diets were completely analyzed before each exercise test by a nutritionist. Participants, with the help of a dietician who was available during meals on test days, filled out food diaries. The amount of energy, protein, carbohydrates, fats and fiber were then analyzed using a commercially available program.

The experiment was conducted in accordance with the Declaration of Helsinki. The study protocol was approved by the Ethical Committee of the Medical University of Poznan

Inclusion Criteria:

• valid medical examination,
• consent of the legal guardian of the underage athlete to participate in the study,
• Training experience a minimum of three years
• Student of a sports championship school team,
• ompletion of the exercise test in the swimming pool - crawl style intensive test (800 m + 200 m + 50 m) on two test deadline

Exclusion Criteria:

• antibiotic therapy,
• supplementation, use of any drugs or oral hormonal contraceptives
• health problems within the last months

Swimmers attending the Sports Championship School Complex