Objectives:To examine evidence of exercise-induced bronchoconstriction (EIB) defined as ≥10% reduction in forced expiratory volume in one second (FEV 1 ) and exercise-induced arterial hypoxemia (EIAH) defined as ≥4% reduction in oxygen saturation (SpO 2 ) from before to after participation in the Norseman Xtreme Triathlon. Secondarily, to assess whether changes in FEV 1 and SpO 2 are related to respiratory symptoms, training volume, and race time. Methods: In this quasi-experimental non-controlled study, we included 63 triathletes (50♂/13♀) aged 40.3 (±9.0) years (mean ± SD). Fifty-seven (46♂/11♀) measured lung function and 54 (44♂/10♀) measured SpO 2 before the race, 8-10 minutes after the race (post-test 1) and the day after the race (post-test 2). Respiratory symptoms and training volume were recorded with modified AQUA questionnaire. ANOVA for repeated measures was used to detect differences in lung function and SpO 2 .Statistical significance was accepted at 0.05 level. Results: Twenty-six participants (46%) presented with EIB at post-test 1 and 16 (28%) at post-test 2. Lung function variables were significantly reduced from baseline to post-test 1 and 2. Thirty-five participants (65%) showed evidence of mild to moderate EIAH. No significant correlations were observed except a weak correlation between maximal reduction in FEV 1 and respiratory symptoms (r = 0.35, P = .016). Conclusion: Our results demonstrated that 46% of the participants presented with EIB and 65% showed evidence of EIAH after the Norseman Xtreme Triathlon. Changes in FEV 1 and SpO 2 were not correlated to weekly training hours or race time. We observed a weak correlation between maximal reduction in FEV 1 and respiratory symptoms. K E Y W O R D S exercise-induced arterial hypoxemia, exercise-induced bronchoconstriction, triathletes | 1009 STENSRUD ET al.