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Abstract

Background: While exposure to greater effective doses of ozone (O₃) (product of the concentration of O₃, ventilation, and duration of exposure) during exercise results in greater decrements in pulmonary function, the effect of matched effective doses of O₃ at different exercise intensities on pulmonary function has seldomly been explored. Aim: To investigate whether exercise performed in O₃ results in greater decrements in forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV₁) when performed at a higher-intensity for a shorter duration compared to a moderate-intensity exercise performed longer when the effective dose of O₃ is matched across intensities. Methods: Fourteen endurance-trained athletes (6 female, VO₂max=56.9±9.6 ml/kg/min) completed steady-state exercise bouts at a moderate-intensity (average duration =43:53) and heavy-intensity (average duration =66:07) with different air conditions (180 ppb O₃ and room air ≤10 ppb) in a randomised fashion. Cumulative ventilation was controlled across trials to control for effective dose. Spirometry and dyspnea were assessed before, during, and after each exercise bout, while breathing mechanics were only assessed during exercise. Results: Compared to baseline measures using mixed-effects modeling, O₃ exposure resulted in worsened measures of FEV₁ (-7.48%, p-value<0.001) and FVC (-2.55%, p-value=0.014) independent of intensity immediately post-exercise. Independent of pollution exposure immediately post-exercise, moderate-intensity exercise resulted in worsened FEV₁ (-2.89%, p-value=0.026) and FVC (-2.07%, p-value=0.043). While differences in spirometry from moderate-intensity O₃ exposure were not significantly worse than heavy-intensity O₃ exposure immediately post-exercise, when all post-exercise timepoints were included in the model, differences in FEV₁ (-3.80%, p<0.001) and FVC (-3.45%, p<0.001) were significant. Changes in breathing frequency and tidal volume were only seen with comparison of the moderate-intensity O3 exposure to the room air, moderate-intensity control. Conclusion: Differences in FEV₁ and FVC were observed with O₃ exposure and moderate-intensity exercise immediately post exercise and between O₃ exposures (in favour of worsened responses during moderate-intensity exercise) when a model that included measurements from all post-exercise timepoints was used. Findings from this study suggest that to minimize the effect of O₃ pollution on acute lung function, endurance athletes should aim to exercise for a shorter duration at a higher intensity.