Characterization of Aerosol Generation During Various Intensities of Exercise.

BACKGROUND

Characterization of aerosol generation during exercise can inform the development of safety recommendations in the face of COVID-19.

RESEARCH QUESTION

Does exercise at various intensities produce aerosols in significant quantities?

STUDY DESIGN AND METHODS

In this experimental study, subjects were eight healthy volunteers (six men, two women) who were 20 to 63 years old. The 20-minute test protocol of 5 minutes rest, four 3-minute stages of exercise at 25%, 50%, 75%, and 100% of age-predicted heart rate reserve, and 3 minutes active recovery was performed in a clean, controlled environment. Aerosols were measured by four particle counters that were place to surround the subject.

RESULTS

Age averaged 41 ± 14 years. Peak heart rate was 173 ± 17 beat/min (97% predicted); peak maximal oxygen uptake was 33.9 ± 7.5 mL/kg/min; and peak respiratory exchange ratio was 1.22 ± 0.10. Maximal ventilation averaged 120 ± 23 L/min, while cumulative ventilation reached 990 ± 192 L. Concentrations increased exponentially from start to 20 minutes (geometric mean ± geometric SD particles/liter): Fluke >0.3 μm = 66 ± 1.8 → 1605 ± 3.8; 0.3-1.0 μm = 35 ± 2.2 → 1095 ± 4.6; Fluke 1.0-5.0 μm = 21 ± 2.0 → 358 ± 2.3; P-Trak anterior = 637 ± 2.3 → 5148 ± 3.0; P-Trak side = 708 ± 2.7 → 6844 ± 2.7; P-Track back = 519 ± 3.1 → 5853 ± 2.8. All increases were significant at a probability value of <.05. Exercise at or above 50% of predicted heart rate reserve showed statistically significant increases in aerosol concentration.

INTERPRETATION

Our data suggest exercise testing is an aerosol-generating procedure and, by extension, other activities that involve exercise intensities at or above 50% of predicted heart rate reserve. Results can guide recommendations for safety of exercise testing and other indoor exercise activities.