Ozone exposure limits cardiorespiratory function during maximal cycling exercise in endurance athletes

Ground-level ozone (O₃) is a potent air pollutant well recognized to acutely induce adverse respiratory symptoms and impairments in pulmonary function. However, it is unclear how the hyperpnea of exercise may modulate these effects, and the subsequent consequences on exercise performance. We tested the hypothesis that pulmonary function and exercise capability would be diminished, and symptom development would be increased during peak real-world levels of O₃ exposure compared to room air. Twenty aerobically trained participants [13M, 7F; maximal O₂ uptake (𝑉ሶ O₂max), 64.1 ± 7.0 mL·kg-¹·min-¹)] completed a three-visit double-blinded, randomized crossover trial. Following a screening visit, participants were exposed to 170 ppb O₃ or room air (<10 ppb O₃) on separate visits during exercise trials, consisting of a 25-minute moderate intensity warmup, 30-minute heavy intensity bout, and a subsequent time-to-exhaustion (TTE) performance test. No differences in O₂ uptake or ventilation were observed during submaximal exercise between conditions. During the TTE test, we observed significantly lower end-exercise O₂ uptake (-3.2 ± 4.3%, p=0.004), minute ventilation (-3.2 ± 6.5%, p=0.043), tidal volume (-3.6 ± 5.1%, p=0.008), and a trend towards lower exercise duration in O₃ compared to room air(-10.8 ± 26.5%, p=0.092). As decreases in O₂ uptake and alterations in respiratory pattern were also present at matched time segments between conditions, a limitation of oxygen transport seems likely during maximal exercise. A more comprehensive understanding of the direct mechanisms that limit oxygen transport during exercise in high-pollutant concentrations is key for mitigating performance changes.