Exercise-induced bronchoconstriction (EIB) increases in cold and dry air and decreases in humid air in subjects with asthma. Few reports have reported on the effect of humid environment upon exercise capacity in subjects with EIB.

The primary aim of the present study was to examine the effect of changing the humidity of the environmental air upon exercise capacity measured by peak oxygen uptake (V˙O_{2 peak}), peak ventilation (V˙E_peak) and peak running speed (V˙_peak) and secondarily to assess the influence of environmental humidity upon EIB in subjects suffering from EIB.

Twenty subjects (10–45 years old, male/female:13/7) with diagnosed EIB performed exercise testing under standardised, regular environmental conditions, 20.2°C (±1.1) and 40% (±3.3) relative humidity [mean (±sd)], and under standardised humid environmental conditions; 19.9°C (±1.0) and 95% (±1.7) relative humidity in random order on separate days. Lung function was measured before and 1, 3, 6, 10 and 15min after exercise. Heart rate (HR), oxygen uptake (V˙O₂), respiratory gas exchange ratio (RER), breathing frequency (BF) and minute ventilation (V˙E) were measured during exercise.

V˙O_{2 peak} and V˙_peak increased significantly from 40% to 95% relative humidity of the environmental air, 4.5% and 5.9%, respectively ( ). HR_peak increased significantly in the humid environment, while BF_peak decreased significantly. RER_peak and V˙E_peak did not change significantly. Post-exercise reduction in FEV₁ (ΔFEV₁) and FEF₅₀ (forced expiratory flow at 50% of FVC) (ΔFEF₅₀) significantly decreased after exercise in a humid environment as compared to regular conditions, ΔFEV₁: 12% (7,17) vs. 24% (19,29) [mean (95% confidence intervals)], respectively, ΔFEF₅₀: 20% (12,29) vs. 38% (30,46), respectively (P<0.001).

Exercise capacity (V˙O_{2 peak} and V˙_peak) markedly improved during exercise in humid air in subjects with EIB, whereas EIB was reduced to the half.