Characterization of Aerosol Generation During Various Intensities of Exercise

Abstract

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.

Keywords: aerosol; exercise; exercise testing.

Figure 1

A, Inside view of Colorado Altitude Training tent and materials. B, The image of a subject exercising inside the clean tent shows external physiologic monitoring equipment and P-Trak 8525 particle counter (Fluke Corporation) behind subject. Black conductance tubing in front of the subject is connected to a second P-Trak, and a third P-Trak is placed to the subject’s side. A Fluke 985 particle counter (TSI Incorporated) is in front of the subject.

Figure 2

Cardiopulmonary exercise data includes heart rate, oxygen uptake, and minute volume of ventilation. BTPS = body temperature and pressure, saturated; HRR = predicted heart rate reserve; Vo₂ = oxygen uptake

Figure 3

Individual subject graphs of all Fluke-measured (Fluke Corporation) particles >0.3 microns vs time during the exercise protocol. Arithmetic mean, geometric mean, and passive room clearance data are also plotted. Note: The Y-axis is truncated at 5,000 particles/L so that values for Subject 8 at 17 minutes (16,035 particles/L) and at 20 minutes (19,891 particles/L) are off the scale. HRR = predicted heart rate reserve.

Figure 4

Concentrations of particles (per liter) counted by the Fluke particle counter (Fluke Corporation) are displayed in the overall range of 0.3 to 5.0 microns with subgroups of particles 0.3 to 1.0 microns and 1.0 to 5.0 microns during the exercise protocol. Data represent geometric means of the data from eight subjects. Cumulative ventilation in liters (Fluke particles 0.3 to 5.0 μm) is also displayed on a separate axis. HRR = predicted heart rate reserve.

Figure 5

Concentrations of particles 0.02 to 1.0 microns from the P-track sensors (TSI Incorporated) (anterior, side, and back) during the exercise protocol are displayed along with cumulative ventilation. Data represent geometric means of data from eight subjects. Cumulative ventilation in liters is also displayed on a separate axis. HRR = predicted heart rate reserve.

Figure 6

Concentrations of particles (per liter) measured by the Fluke particle counter (Fluke Corporation) are displayed in the overall range of >0.3 microns with subgroups of particles 0.3 to 1.0 microns and 1.0 to 5.0 microns during the exercise protocol. Data represent means of the data from five subjects comparing a no mask trial vs a trial measuring oxygen uptake. HRR = predicted heart rate reserve; Vo₂ = oxygen uptake.