American Football and COVID-19: reducing on-field exposures to respiratory particles

The Sport Journal
September 3, 2021

Abstract
American football poses unique challenges to protecting the health of athletes both on and off the field. While off-field activities likely pose the greatest risk of COVID-19 transmission among members of the same team, on-field activities may pose transmission risks from one team to another. The findings of this study suggest that, when used in well-ventilated outdoor environments, helmet modifications combining upper and lower visors may help reduce on-field respiratory transmission risks with relatively minimal effects on athletic performance. These findings may offer practical insights to team physicians and athletic trainers as they seek strategies to protect athletes against on-field transmission of COVID-19 in the weeks and months ahead.

Introduction
American football poses unique challenges to preventing COVID-19 transmission on the playing field. Mask usage and social distancing are effective measures for reducing off-field transmission, but their use during play is impractical. While off-field activities likely pose the greatest risk of disease transmission among members of the same team, on-field activities may pose transmission risks from one team to another. As competitive sports resume during the ongoing pandemic, studies are needed to describe and validate the effectiveness of strategies that not only reduce on-field COVID-19 transmission risks, but that are widely available to athletes at all levels, including youth leagues. This study examines the suitability of practical helmet modifications to minimize on-field transmission of COVID-19 during American football.

Since the onset of the COVID-19 pandemic, a variety of approaches have been deployed to protect athletes from SARS-CoV-2 with an emphasis on mitigating respiratory exposures, reducing contact with high-touch surfaces, and minimizing high-risk social interactions. Approaches have varied from complete isolation of league personnel as demonstrated by the “bubble” approach implemented by the National Basketball Association (1), to the National Football League’s implementation of comprehensive protocols detailing procedures and facility modifications designed to minimize risks to athletes and staff (2). Procedural modifications have been complemented by the development of athletic equipment designed to protect against SARS-CoV-2 exposures. Examples of such equipment include the Mouthshield developed by the National Football League (NFL) and Oakley, which protects against the transmission of respiratory droplets while maximizing athlete comfort (3). At the collegiate level, a variety of reports describe collaborations between Sports Medicine staff and engineers to develop protective equipment (e.g., 4). While numerous strategies have been described, their practicality and efficacy are not widely reported. Further, since most innovations in American football equipment have focused on protecting against injuries from impact (e.g., concussion), for example (5,6), few testing methods exist for evaluating the efficacy of protective devices designed to reduce on-field transmission of infectious disease. The work reported here describes helmet and mouthguard modifications designed to reduce on-field transmission of SARS-CoV-2 and their efficacy in laboratory studies with a simulated respiratory challenge.

Methods
Helmet Modifications

Helmets were outfitted with modified visors or a mouthguard prototype and subjected to aerosol challenges to assess their ability to block simulated respiratory droplets projected both outward (from inside the helmet) and inward (from outside the helmet); the mouthguard modification was evaluated separately. Modifications investigated include four helmet-mounted visor configurations: 1.) no visor (i.e., no modification), 2.) upper visor only, 3.) lower visor only, 4.) combined lower/upper visors, and 5.) a prototype mouthguard modified to loosely cover the nose and filter respired breath (Mouthshield) (Fig 1a). Emphasis was placed on modifications that can be readily assembled from familiar materials available through athletic equipment distributors. Polycarbonate upper visors were obtained from NIKE, Inc. (Beaverton, OR, USA) and mounted as intended to the upper half of the helmet facemask. Lower visors were configured from the same material as the upper visors but were rotated 180 degrees and trimmed to fit the lower half of the helmet facemask to improve ventilation and athlete comfort. Two mounting clips were used for each configuration. The mouth shield innovation consists of a simple polymer-based assembly that converts a conventional American football mouthguard into an integrated face shield and low pressure-drop filter device. A more complete description of the Mouthshield innovation is available elsewhere (7).

Particle Challenges and Measurement

A commercial airbrush (Photo Finish Airbrush Company, Greeneville, SC, USA) filled with 2 mL of deionized water was used to generate aerosols representative of exhaled breath. The air brush was administered for a duration of 10 seconds per spray, a procedure that was replicated six times for each of the four helmet modifications and the Mouthshield. A TSI (Shoreview, MN, USA) Aerotrak 9306 optical particle counter (OPC) linked to sampling ports located within the nostrils of a headform (Bepholan) was used to quantify the average number of particles measuring 0.3 to 25 mm in diameter during each 10 s spray. The positions of the airbrush and headform relative to the helmet-mounted visors and mouthpiece were 30 cm apart and alternated between two different testing configurations: 1) containment of aerosols projected outward from inside the helmet (Figure 1b,c) and 2) blockage of aerosols projected inward from outside the helmet (Figure 1d).

Figure 1

Note. Summary of helmet modifications, test setup and resulting particle retention or blockage. A, Four different helmet visor modifications were assembled and investigated (m=Mouthshield not shown). B, Illustration of test setup used to evaluate outward retention of particles generated from within the helmet. C, Close-up view of outward test setup showing placement of the airbrush nozzle relative to the helmet facemask and distance separating the points of particle generation and measurement. D, Illustration of test setup used to evaluate inward blockage of particles generated from outside the helmet.

RESULTS
Resulting particles closely approximated size distributions and velocities reported in the literature for exhaled breath (8, 9). Combining upper and lower visors reduced both outward and inward transmission of particles by >99% (by mass). Lower visors were more effective than upper visors at reducing outward transmission of droplets, whereas either visor helped reduce inward transmission similarly. Alone, upper visors, which are mounted above the mouth, offered virtually no retention of particles projected outward. All modifications were more effective against particles of 1-25 mm diameter than the smallest particles measuring 0.3 to 1 mm.

Table 1
No. (%) of particles (by mass), mean (SD), measuring 0.3 – 25 mm in diameter retained (in outward challenges) or blocked (in inward challenges) by each helmet modification relative to the positive control (no helmet).

DISCUSSION
While N95 respirators are preferable to faceshields for protection against COVID-19 transmission (10, 11), particularly in poorly ventilated environments, they are impractical for prolonged use during high-intensity athletic activities. Helmet-mounted visors effectively reduced the transmission of aerosol droplets measuring 0.3 to 25 mm and passed testing recommended by the National Operating Committee on Standards for Athletic Equipment (NOCSAE) (12). National Collegiate Athletic Association (NCAA) athletes wore the modified helmets during competitive regular season play. Athletes reported that trimming the lower visors improved comfort, but the visor’s placement can restrict removal and reinsertion of mouthguards. Fogging of the lower visor reduced downward visibility, but visually indicates the visor’s efficacy against outward projection of respiratory droplets. When used in well-ventilated outdoor environments, helmet modifications combining upper and lower visors may help reduce on-field respiratory transmission risks with relatively minimal effects on athletic performance.

CONCLUSIONS
Helmet modifications combining upper and lower visors reduced both outward and inward transmission of particles measuring 0.3 to 25 mm by >99% (by mass), suggesting that their use may help reduce on-field transmission of COVID-19 via respiratory droplets with relatively minimal effects on athletic performance. When used without a lower visor, upper visors, which are mounted above the mouth, offered virtually no retention of particles projected outward.

APPLICATIONS IN SPORT
The physical demands of athletic competition, particularly American football, pose unique challenges to protecting athletes from COVID-19 exposures during play. Coaches, athletic trainers, and sports physicians have developed robust strategies to protect athletes off the field, but options for on-field protection remain limited. The research herein proposed simple helmet modifications and a mouthpiece-mounted face shield that demonstrably reduced both the outward projection and inward penetration of simulated respiratory droplets in controlled laboratory studies. The interventions passed testing recommended by the NOCSAE and have been worn during competitive regular season play by NCAA athletes. While these interventions cannot offer the same level of protection as fitted masks and respirators, they may help reduce the risks of on-field transmission of disease via respiratory droplets in otherwise well-ventilated outdoor environments.

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