Differences between swimming and running as stimuli for exercise-induced asthma

Thirteen children each exercised for 6 min by running on a treadmill and by tethered swimming, breathing air at room temperature and either 8% or 99% relative humidity continuously. Ventilation, gas exchange and heart rate were closely matched in all four tests in each child, with a mean oxygen consumption of 32.3±1.7ml·min^-1·kg^-1. The post-exercise fall in FEV₁ expressed as a percentage of the baseline FEV₁ (δFEV₁) was significantly greater after running compared with swimming breathing either humid or dry air. The δFEV₁ was also related to respiratory heat loss (RHL) calculated from measurements of inspired and expired gas temperature and humidity. At a standardised RHL, the difference between running and swimming was highly significant [δFEV₁ (%) ± SE=39±5 and 28±4 respectively, p<0.01]. These experiments suggest that the type of exercise influences the severity of exercise-induced asthma even under conditions of the same metabolic stress and respiratory heat loss.