Repeated-Sprint Training in Normobaric Hypoxia Enhances Aerobic and Anaerobic Performance Without Altering Hematological Parameters in Athletes

<title>Abstract</title> <p>The purpose of this study was to explore the effects of four weeks of intermittent hypoxic (IHT) repeated sprint training administered to athletes via a hypoxia device at sea level on their hematological parameters, anaerobic performance, and aerobic capacity. Twenty-eight subjects with moderate training levels participated voluntarily in the study. The subjects were randomly assigned to either an experimental (hypoxia, n=14) or a control (n=14) group. The subjects in the experimental group received repeated sprint training with a resistance cycle under normobaric hypoxic conditions equivalent to approximately 2550 meters in altitude, with two sessions per week for 4 weeks. The subjects in the control group performed the same training as the experimental group under normoxic conditions.. Prior to and following this research, anaerobic performance, aerobic performance, and hematological parameters (HGB, HCT, RBC, MCV, and MCHC) were assessed. Two-way ANOVA with mixed measurements was used to analyze the data. Significant increases in anaerobic power and anaerobic capacity values were detected in the experimental group (p&lt;0.05). Significant differences were observed in the VO₂ max values in terms of measurement and group*measurement interactions, and it was determined that hypoxic training positively affected aerobic capacity (p&lt;0.05). Conversely, no significant changes were detected in body weight or basic hematological parameters such as hemoglobin, hematocrit, or erythrocyte count (p&gt;0.05). Overall, four weeks of IHT repeated sprint training performed with a hypoxia device at sea level is an effective method, particularly for enhancing athletes’ anaerobic performance and aerobic capacity. However, short-term hypoxic exposure did not elicit significant hematological adaptations. Trial Registration: Australian New Zealand Clinical Trials Registry (ANZCTR) ACTRN12626000865314. Registered 15 July 2026.</p>