Repeated-sprint training in normobaric hypoxia improves aerobic and anaerobic capacity without altering hematological parameters in athletes

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 performed the repeated-sprint training protocol on a resistance-loaded cycle ergometer (120 W) while breathing a normobaric hypoxic gas mixture equivalent to approximately 2550 m 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. A significant group × time interaction indicated a greater increase in anaerobic capacity in the experimental group than in the control group ( p = 0.002); anaerobic power increased significantly over time in both groups, with a significant overall group difference ( p = 0.023) but no significant group × time interaction ( p = 0.079). A significant group × time interaction was also observed for predicted VO₂max ( p < 0.05), indicating a greater improvement in aerobic capacity in the experimental group. Conversely, no significant changes were detected in body weight or basic hematological parameters such as hemoglobin, hematocrit, or erythrocyte count ( p > 0.05). Overall, within this specific four-week protocol and hypoxic dose, IHT repeated sprint training performed with a hypoxia device at sea level appears effective, 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.