Link between exercise intensity and infection risk – Neuroscience News

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Summary: The researchers identify the level of exertion where the emission of aerosol particles increases exponentially, offering an explanation as to why exercise intensity may be linked to the transmission of infections.

Source: TUM

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

Many people were also known to have been infected with the SARS-CoV-2 virus while exercising indoors.

However, it was unclear how exercise intensity was related to the concentration of aerosol particles in the exhaled air and the actual amount of aerosols exhaled by an individual per minute and therefore potential risk. spread of infectious diseases such as SARS-CoV-2.

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

New methodology provides 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 of Fluid Mechanics and Aerodynamics at the Universität der Bundeswehr München, have developed a new method of investigation to study these questions.

Their experimental device first filtered the aerosols already present in the ambient air. In the subsequent ergometer stress test, the test subjects inhaled the purified air through a special mask covering 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 can escape. The amount of aerosol particles emitted per minute was then measured and directly related to the current performance of healthy test subjects, aged 18-40.

Moderate aerosol emissions at medium effort

The researchers were thus able to study for the first time how many aerosol particles are exhaled per minute by an individual at different levels of exercise intensity.

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

This means that an individual who weighs 75 kilograms reaches this threshold at 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.

The aerosol emissions of the well-trained athletes were significantly higher than those of the untrained test subjects at maximal exercise due to their much higher minute ventilation. The researchers found no significant differences in particulate emissions between the sexes.

Protective measures are important for high intensity workouts

Although aerosol experiments only provide indirect knowledge of 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 population poorly immunized threatens to overwhelm the healthcare system.

“Based on our results, we distinguish between moderate endurance training with an intensity of up to 2 watts per kilogram of body weight and high to maximum intensity training. Due to the large increase in aerosol emissions during high-intensity workloads beyond this initial baseline, special protective measures are needed where there is a high risk of infections with serious consequences,” says Prof. Wackerhage, head of the study.

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

“Ideally, this type of training should take place outdoors. If this is not possible, tests should be carried out to ensure that no infected person is in the room. Participants must also maintain an appropriate distance and a high-efficiency ventilation system must operate.

“In addition, infection risks are reduced by training at lower intensities and keeping sessions shorter. It might also be possible for fit young athletes to wear masks during training.

At low workloads such as easy to moderately intense endurance training, Prof Wackerhage adds, less protection is needed and the risk of infection can be controlled with distancing and ventilation systems.

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

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About this exercise and infection research news

Author: Henrike Boden
Source: TUM
Contact: Henrike Boden – TUM
Image: Image is in public domain

Original research: Free access.
Aerosol particle emission increases exponentially above moderate exercise intensity, resulting in overemission during maximal exerciseby Henning Wackerhage et al. PNAS


Aerosol particle emission increases exponentially above moderate exercise intensity, resulting in overemission 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, lung ventilation can increase more than 10 times and therefore users will exhale a greater volume of air containing aerosols. However, we currently do not know how exercise affects exhaled aerosol particle concentration and overall aerosol particle emission.

Therefore, we developed a method to measure in parallel the concentration of aerosol particles in the exhaled air, the pulmonary ventilation and the emission of aerosol particles at rest and during a graded exercise test up to to exhaustion. We used this method to test eight women and eight men in a descriptive study.

We found that the aerosol particle concentration in exhaled air increased significantly from 56 ± 53 particles/litre at rest to 633 ± 422 particles/litre 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 was no gender difference in aerosol particle emission, but endurance-trained subjects emitted significantly more aerosol particles during maximal exercise than untrained subjects. Overall, aerosol particle emission increased moderately up to an exercise intensity of about 2 W/kg and exponentially thereafter.

Together, these data could partly explain superspreading events, especially during high-intensity group exercise indoors, and suggest that strong infection prevention measures are needed, especially during exercise. at an intensity greater than ∼ 2 W/kg.

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

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