The purpose of this study is to examine how breathing air with different oxygen concentrations (higher or lower than normal) during high-intensity interval training affects:

• Aerobic capacity (VO₂max)
• Ventilatory thresholds
• Blood lactate levels
• Perceived exertion This research aims to better understand how oxygen availability influences physiological adaptations to exercise.

If you agree to participate, you will undergo the following:

Baseline testing:

• Cardiopulmonary exercise test (cycling until exhaustion)
• Measurement of oxygen consumption, heart rate, and ventilatory thresholds
• Blood lactate measurement (finger prick)

Training intervention (3 weeks):

• 3 sessions per week (total of 9 sessions)
• High-intensity interval training (Tabata protocol: 8 × 20 seconds effort / 10 seconds rest)
• Exercise performed on an air-resistance cycle ergometer

During training, you will breathe either:

• Hyperoxic air (high oxygen concentration) or
• Hypoxic air (low oxygen concentration) You will be randomly assigned to one of these conditions.

Post-intervention testing:

• Same assessments as baseline

The risks associated with this study are similar to those encountered during high-intensity exercise:

• Fatigue
• Muscle soreness
• Shortness of breath
• Temporary discomfort from finger-prick blood sampling

Breathing altered oxygen concentrations (hypoxia or hyperoxia) may induce:

• Mild dizziness
• Increased breathing effort (hypoxia)
• Sensations of ease or altered effort perception (hyperoxia) All sessions are supervised by trained personnel, and safety monitoring is ensured throughout the study

You may benefit from:

• Improved physical fitness
• Detailed physiological assessment (VO₂max, thresholds) However, no direct health benefit is guaranteed. Your participation is entirely voluntary.
• You may withdraw at any time
• You do not need to provide a reason
• Withdrawal will not affect your academic or professional standing

All collected data will be:

• Anonymized
• Stored securely
• Used only for research purposes Your identity will not be disclosed in any publication. Data will be handled in accordance with applicable data protection regulations (GDPR).

You have the right to:

• Access your data
• Request correction or deletion where applicable

Inclusion Criteria:

• recreationally active
• male
• 18-35 years old

Exclusion Criteria:

• engaged in professional or elite-level sports training
• cardiovascular, pulmonary, metabolic, or neurological disease
• taking medications known to influence cardiovascular or metabolic responses to exercise To minimize potential confounding factors, participants were instructed to refrain from strenuous physical activity, alcohol consumption, caffeine intake, and smoking for at least 24 hours before each testing session, in accordance with standard exercise testing procedures recommended in exercise physiology guidelines

Data are collected for this study only. The experiments opens new questions and so new data collection