Studies show that adults exercising vigorously react more to ozone exposure than do adults at rest.
People working or exercising increase their breathing rate, so that they inhale more ozone and thus a higher dose reaches the target tissues of the bronchioles and alveoli. In controlled tests, a 5 to 10 percent reduction occurred in volunteers engaged in moderate exercise for 6.5 hours at just 80 ppb. Athletic ability, as measured by performance on stationary bikes or treadmills, has been shown to be poorer at 180 ppb than among controls performing in normal air. Ozone concentrations can make the small bands of muscles that help control breathing more sensitive to dry air, cold or dust, so they contract, narrowing the airways and making breathing more difficult. In five cities studied by researchers in Massachusetts, hospital admissions for pneumonia and flu were highest in the cities with higher maximum ozone levels and particulate levels.