Breathing dynamics and aerosol emissions from young people during cycling exercise

Physical activity is important to maintain good physical and mental health. However, transmission of respiratory diseases in exercise facilities indicates the importance of maintaining good indoor air quality in these environments. Aerosols exhaled by infected individuals are a significant source of transmission of respiratory diseases. Thus, understanding breathing behaviour during exercise is critical. This study investigated breathing dynamics and aerosol emissions during cycling exercise and rest from 21 healthy participants (10 female and 11 male subjects, 19–37 years old). Key features such as minute ventilation, breathing patterns, peak inhalation and exhalation flow rate, and respiratory frequency were analysed. The results showed that exercise significantly increased minute ventilation, and the variations of breathing flow rate over time followed a sinusoidal pattern. During maximal exercise, peak inhalation and exhalation flow rates were more than three times higher than those at rest, and respiratory frequency was approximately twice as high as that at rest. In addition, the size distribution of aerosols from breathing during exercise was mainly in the range of 0.3–2.5 μm. Exercise significantly increased aerosol emissions of breathing, with average emission rates during maximal exercise being 9.0 times higher than at rest. These findings suggest that physical activity greatly affects breathing dynamics and aerosol emissions. Exercise facilities have unique characteristics that differ from other indoor settings. This study provides essential information that can serve as boundary conditions for computational fluid dynamics studies, aiding further research on aerosol dispersion, infection risk assessment, and the development of energy-efficient mitigation strategies for exercise facilities.