Urban Air Pollution and Cardiopulmonary Function During Outdoor Exercise in Lahore, Pakistan: A Within-Subjects Field Study

Abstract

Lahore regularly records among the highest urban particulate matter (PM2.5) concentrations in the world, particularly during the autumn–winter smog season. This within-subjects field study examined whether acute outdoor exercise performed on a high-air-quality-index (High-AQI) day produces greater cardiopulmonary strain than the same exercise bout performed on a low-AQI day. Thirty healthy recreational runners and cyclists (age 26.3 ± 4.1 years) completed a standardized 30-minute moderate-intensity outdoor exercise bout (70% of estimated maximum heart rate) on a paved urban route in Lahore under two conditions in randomized order: A Low-AQI day (ambient PM2.5 ≈ 38 µg/m³) and a High-AQI/smog day (ambient PM2.5 ≈ 182 µg/m³). Spirometry (FEV1, FVC, PEF) was assessed immediately before and after exercise on both days; peripheral oxygen saturation (SpO₂), one-minute heart-rate recovery (HRR1), respiratory symptom score, and rating of perceived exertion (RPE) were also recorded. Results: FEV1 declined significantly after exercise on the High-AQI day (M = 0.06 L, p < .001) but not on the Low-AQI day (p = 0.320), and the magnitude of FEV1 decline was significantly greater on the High-AQI day (p = 0.006, d = 0.54). Peak expiratory flow showed a parallel pattern (p = 0.008). Post-exercise SpO2 was significantly lower (p < .001) and heart-rate recovery significantly blunted (p < .001) on the High-AQI day. FEV1 decline correlated positively with individual PM2.5 exposure during exercise (r ≈ .64). Acute exposure to elevated ambient PM2.5 during outdoor exercise in Lahore was associated with measurable bronchoconstriction, reduced oxygenation, and impaired autonomic recovery relative to a lower-pollution day, supporting public-health guidance to modify outdoor training timing, location, or intensity during high-AQI periods.