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
Age range
19 Years – 35 Years
Sex
MALE
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The trial coordinator is the person who runs the study day to day. These cover the practical side — logistics, costs, and what taking part would actually mean for your life. The study team confirms whether you meet the criteria; these are questions to ask, not a sign you qualify.
A starting point for the conversation — always confirm anything about your own eligibility, costs, and care with the study team and your doctor.
maximal oxygen uptake (VO₂max)
Timeframe: From enrollment to the end of protocol at 3 weeks