Link Between Exercise Intensity and Infection Risk

Summary: The researchers identify the level of exertion at which aerosol particle emission increases exponentially, offering an explanation for why exercise intensity may be linked to infection transmission.

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Before the study, it was known that the respiratory volume of untrained people increases from about 5 to 15 liters per minute at rest to more than 100 liters per minute during exercise. In fact, highly trained athletes reach levels of 200 l/min.

It was also known that many people have been infected with the SARS-CoV-2 virus by exercising indoors.

However, it was unclear how exercise intensity was related to the concentration of aerosol particles in exhaled air and the actual number of aerosols exhaled by an individual per minute, and thus to the potential risk of spreading infectious disease. like SARS-CoV-2.

However, this information is urgently needed, for example, to design mitigation measures for school gyms and other indoor sports facilities, fitness studios, or nightclubs to avoid closures in the event of severe waves of infection.

New methodology offers individually measurable aerosol values

A team led by Henning Wackerhage, Professor of Exercise Biology at the Technical University of Munich (TUM), and Professor Christian J. Kähler, Director of the Institute for Fluid Mechanics and Aerodynamics at the Universität der Bundeswehr München, has developed a new research method to study these issues.

Their experimental apparatus initially filtered out aerosols already present in ambient air. In the subsequent ergometer stress test, the test subjects inhaled the purified air through a special mask that covered the mouth and nose.

Exercise intensity was gradually increased from rest to the point of physical exhaustion. The mask was connected to a two-way valve through which only exhaled air could escape. The number of aerosol particles emitted per minute was then measured and directly linked to the current performance of healthy test subjects aged 18 to 40 years.

Moderate aerosol emissions at medium effort

In this way, the researchers were able to investigate for the first time how many aerosol particles an individual exhales per minute at various levels of exercise intensity.

The result: Aerosol emissions during exercise initially increased only moderately up to an average workload of around 2 watts per kilogram of body weight. Above that point, however, they increased exponentially.

That means a person weighing 75 kilograms reaches that threshold with an ergometer reading of around 150 watts. This corresponds to a moderate effort for a casual athlete, perhaps comparable to the exercise intensity of a moderate jog.

Aerosol emissions from well-trained athletes were significantly higher than those from untrained test subjects at maximal effort due to their much higher minute ventilation. The researchers found no significant differences in particulate matter emissions between genders.

Protective measures are important for high intensity training

Although aerosol experiments only provide indirect insight into the amount of virus in exhaled air, the study suggests useful starting points for managing indoor activities when a wave of infection combined with a poorly immunized population threatens to overwhelm the immune system. Health.

“According to our results, we distinguish between moderate resistance training with an intensity of up to 2 watts per kilogram of body weight and high to maximum intensity training. Due to the strong increase in aerosol emissions in high-intensity workloads above that initial reference point, special protective measures are needed in case of a high risk of infections with serious consequences”, says study leader, Professor Wackerhage.

Exercise intensity was gradually increased from rest to the point of physical exhaustion. The image is in the public domain

“Ideally, that type of training would move outdoors. If that is not possible, tests should be done to ensure there are no infected people in the room. Participants must also maintain adequate distance and a high-efficiency ventilation system must be in operation.

“Also, infection risks are reduced by training at lower intensities and keeping sessions shorter. It could also be possible for young and fit athletes to wear masks while training.”

With low workloads, such as easy to moderately intense resistance training, Professor Wackerhage adds, less protection is needed and the risk of infection can be controlled by ventilation and distancing systems.

The research team is currently conducting experiments to compare aerosol emissions in strength and endurance training and correlate them with the ages and physical characteristics of the test subjects.

See also

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About this exercise and infection research news

Author: Henry Boden
Font: TUM
Contact: Henrike Boden – TUM
Image: The image is in the public domain.

original research: Open access.
“Aerosol particle emission increases exponentially above moderate exercise intensity, resulting in superemission during maximal exercise” by Henning Wackerhage et al. PNAS


Aerosol particle emission increases exponentially above moderate exercise intensity, resulting in superemission during maximal exercise

Many airborne pathogens, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), are transmitted indoors via aerosol particles.

During exercise, pulmonary ventilation can increase more than 10-fold, and therefore athletes exhale a greater volume of air containing aerosols. However, we currently do not know how exercise affects the concentration of aerosol particles in exhaled air and the overall emission of aerosol particles.

Accordingly, we developed a method to measure in parallel the concentration of aerosol particles in expired air, lung ventilation, and aerosol particle emission at rest and during a graded stress test to exhaustion. We used this method to evaluate eight women and eight men in a descriptive study.

We found that the concentration of aerosol particles in expired air increased significantly from 56 ± 53 particles/liter at rest to 633 ± 422 particles/liter at maximum intensity. Aerosol particle emission per subject increased significantly by a factor of 132 from 580 ± 489 particles/min at rest to a super emission of 76,200 ± 48,000 particles/min during maximal exercise.

There were no sex differences in aerosol particle emission, but endurance-trained subjects emitted significantly more aerosol particles during maximal exercise than untrained subjects. In general, aerosol particle emission increased moderately up to an exercise intensity of ~2 W/kg and exponentially thereafter.

Together, these data could partly explain superspreading events, especially during high-intensity indoor group exercise, and suggest that strong infection prevention measures are needed, especially during exercise at intensity exceeding ~2 W/kg.

Investigations of factors influencing aerosol particle generation, such as airway and whole-body hydration status during exercise, are needed.

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