Transmission of SARS-CoV-2 is considered to occur predominantly by inhalation of infectious aerosol. In the first published study of its kind, a UK-wide collaborative team of clinicians and researchers conducted a series of experiments to measure the size and concentration of exhaled particles (up to 20 µm diameter) which are generated in our respiratory tracts and breathed out, during vigorous and high-intensity exercise.

Using a cardiopulmonary exercise test (CPET), 25 healthy participants comprising 13 males and 12 females with a range of athletic abilities, were recruited to undertake four different activities (breathing at rest, speaking at normal conversational volume, vigorous exercise and high-intensity exercise) on a cycle ergometer. The participants breathed into a specially adapted mask which measured airflow and transmitted any particles emitted from their mouth and nose to a particle counter. Experiments were carried out in an orthopaedic operating theatre — an environment of “zero aerosol background”, which allowed the researchers to unambiguously identify the aerosols generated by the participants.

The team found that the size of airborne particles emitted during vigorous exercise was consistent with that of a person breathing at rest. However, the rate at which individuals exhale aerosol mass during vigorous exercise was found to be similar to speaking at a conversational volume.

Jonathan Reid, Director of ESPRC Centre for Doctoral Training in Aerosol Science and Professor of Physical Chemistry in the School of Chemistry at the University of Bristol and scientific lead on the paper, said: “COVID-19 has profoundly impacted sports and exercise, and this study provides a comprehensive analysis of the mass emission rates of aerosol that can potentially carry infectious virus produced from an individual during exercise. Our research has shown that the likely amount of virus that someone can exhale in small aerosol particles when exercising is comparable to when someone speaks at a conversational volume.  The most effective way to reduce risk is to ensure spaces are appropriately ventilated to reduce the risk of airborne transmission.”

The PERFORM 2 (ParticulatE Respiratory Matter to InForm Guidance for the Safe Distancing of PerfOrmeRs in a COVID-19 PandeMic), was supported by the EPSRC, and carried out by a collaborative team from Chelsea & Westminster Hospital, Imperial College London, University of Bristol, Wexham Park Hospital, Royal Brompton Hospital, Guys & St. Thomas NHS Foundation Trust, Royal National Ear Nose and Throat Hospital, Fortius Clinic, and University College London. Experiments were carried out in orthopaedic operating theatres at the Fortius Clinic London.

Paper

A comparison of respiratory particle emission rates at rest and while speaking or exercising by Christopher M. Orton et al. in Communications Medicine.