The Impact of Normobaric Hypoxia-inducing High-Intensity Interval Training Program on the Expression Levels of Selected miRNAs and Running Economy in Endurance-trained Athletes

The objective of this study is to assess the impact of a 6-week High-Intensity Interval Training (HIIT) program under normobaric hypoxic conditions on the expression levels of selected miRNAs and running economy in endurance athletes. The research will be conducted as an experimental study on male track and field athletes specializing in middle and long-distance events (n=32) in four stages. In the first stage, which will last for two weeks, volunteers will be recruited for the experiment, and all participants will undergo somatic measurements using bioelectrical impedance analysis (BIA) to determine body composition. The second stage, which will commence immediately after somatic measurements, will be divided into four parts, during which aerobic performance measurements will be conducted in hypoxia (3000 m above sea level), normoxia, running economy tests, and eccentric contraction-dominant effort measurements. Blood samples will be collected before and after each exercise test for biochemical analyses, and all tests will be conducted with appropriate methodological 3-day intervals. In the third stage of the study, athletes will be randomly assigned to four groups, each consisting of 8 individuals: control, experimental with temporary exposure to hypoxia without training, experimental LLTL, and experimental LLTH. Athletes allocated to the experimental LLTL group will incorporate a 6-week (3 times a week) normoxic HIIT training program into their training plan, while the experimental LLTH group will undergo a 6-week (3 times a week) hypoxic HIIT training program. The training program will be conducted in a hypoxic chamber (two training groups of 4 individuals each) located at the Physiological Basis of Adaptation Laboratory, Bronislaw Czech Academy of Physical Education in Krakow, under the supervision of specialized technical staff, a physician, and a personal trainer, and will commence 3 days after the last exercise test. Training intensity will be monitored using subjective scale for assessing the degree of fatigue during physical activity and tree heart rate zones. The training will be conducted in an AMRAP system, with a ratio of 40 seconds of work and 20 seconds of rest. The final, fourth stage will be conducted similarly to the second stage and will also be divided into four parts, including the aforementioned exercise tests and blood sample collection for biochemical analyses. A 3-day rest period will be implemented between the endurance tests. Additionally, to evaluate the long-term effects of the implemented training program, venous blood samples will be collected 21 days after the exercise tests. LLTH Group (live low-train high): Participants will stay and sleep in normoxic conditions at an altitude of approximately 223 meters above sea level (Krakow, Poland). Training sessions for this group will take place in a normobaric hypoxic chamber at the Krakow Academy of Physical Education, simulating an altitude of 2000-3500 meters above sea level (FiO2, 14.4%), following the designated training protocol. The oxygen fraction in the chamber will be continuously monitored. During their stay in the simulated high-altitude environment, participants will monitor their blood oxygen saturation (SpO2) using a pulse oximeter. LLTL Group (live low-train low): Throughout the entire study period, participants in this group will stay, sleep, and perform training under normoxic conditions at an altitude of approximately 223 meters above sea level (Krakow, Poland). Hypoxia Without Training Group: Participants in this group will stay in a hypoxic chamber at the Krakow Academy of Physical Education, simulating an altitude of 2000-3500 meters above sea level (FiO2, 14.4%), for 50 minutes 3 times a week for 6 weeks. However, they will sleep under normoxic conditions at an altitude of approximately 223 meters above sea level (Krakow, Poland), following the designated protocol. During their stay in the simulated high-altitude environment, participants will monitor their blood oxygen saturation (SpO2) using a pulse oximeter. The oxygen fraction in the chamber will be continuously controlled.