A 35-minute lunch break separated the third and fourth bouts of exercise, according to an UC-D release.

'These data tell us that even at levels currently below the air quality standard, healthy people may experience decreased lung function after just a few hours of moderate to light exercise such as bicycling or walking,' said Schelegle.

'While these changes were fully reversible within several hours, these findings highlight the need to study susceptible individuals, such as asthmatics, at similar ozone concentrations and durations of exposure,' he added.

The results are slated for publication in the Aug 1 issue of the American Journal of Respiratory and Critical Care Medicine.