Another mask to add to your wardrobe?
These masks will not provide protection from Covid-19, however, they may be key to preventing breathing problems into the future for cross-country skiers.
Whilst it may not be news to any of the readers here, but cross-country skiing as a winter sport exposes us to some quite extreme conditions both in training and competition. The FIS cut-off of -4°F (-20°C) was primarily established to prevent cold-based injuries during competition such as hypothermia and frostbite but is well below the cut-off for asthma and its associated symptoms to be exacerbated. Once a threshold of circa 20°F is crossed, the absolute humidity of the air remains very low regardless of the relative humidity due to the curvilinear relationship between the moisture capacity of air, relative humidity and absolute humidity. This means that all cold air is dry air, which has to be heated and humidified to 98°F and 100% humidity in the lungs, then exhaled, causing dehydration in the epithelial tissue of the bronchus and potentially causing inflammation which leads to a narrowing of the airways. This phenomenon, once it affects the ability to exhale by >10% (in relation to the volume of forcefully exhaled air in the first second) is defined as exercise-induced asthma. This can also occur to a lesser extent in non-asthmatics when exercising in cold air, without crossing the threshold for a diagnosis of asthma, this is bronchoconstriction.
Facial skin temperature may have an effect on the extent on bronchoconstriction you experience during exercise in cold temperatures (Gavhed et al. 2000; Koskela et. al 1995) due to temperature sensors in the nose, cheek and forehead. Solutions for this are “buffs”, headbands or hats (toques for those Canadian readers) and fabric taping of those areas, which has the added bonus of preventing frostbite. Skin temperature is also associated with reduced double poling performance wearing a race suit at 7°F (Wiggen et. al 2016) so windproof underlayers and appropriate clothing during training and competition may allow you to perform at your best in extreme cold.
A recent meta-analysis by Mäki-Heikkilä et. al (2020) found that worldwide, circa 20% of cross-country skiers have physician-diagnosed exercise-induced asthma with higher occurrences in female athletes. This is about double the rate of the normal, active human population. Eriksson et. al (2018) found specifically that being a young adolescent, female cross-country skier was a significant risk factor for the development of exercise-induced asthma. Similar tendencies are seen in swimmers (where chlorine acts as an irritant) and long-distance runners (where pollen and air pollution may play a role), so we assume that the accumulation of high ventilation training volume in the presence of an irritant such as cold, dry air is a likely cause of exercise-induced asthma in skiers. Kennedy et. al (2016) found an increase in airway inflammation and frequency of coughing between the dryland training season and competition season in 18 female cross-country skiers. We also see some slight differences based on climate, with Sue-Chu et. al (1996) observing a higher incidence of asthma in drier, inland Sweden compared to the more coastal and damp Norway. We could potentially compare Anchorage and Fairbanks, Alaska in a similar way. However, this discussion is relevant to all skiers who train and compete in temperatures below 20°F on a regular basis across North America.
To prevent asthma attacks athletes are typically prescribed a beta-agonist such as albuterol (salbutamol). This medication has had some negative press in the cross-country ski world recently with Martin Sundby’s suspension and a near-constant flow of criticism directed at the number of Scandinavian athletes who are diagnosed asthmatics. Potential performance-enhancing effects have so far only been found in power-based sports at much larger doses than are usually prescribed for asthma management, with very little evidence to suggest that using albuterol with or without asthma will create any form of performance benefit for cross country skiers who are not asthmatic (Riiser et. al 2020). Nevertheless, there is also some concern that overuse of albuterol may result in reduced effectiveness of the medication over a long period of time.
The other method available to prevent exercise-induced asthma and bronchoconstriction is to use a heat-and-moisture exchanging mask (HME). These have been available for around 30 years for sporting use. The two options you may be familiar with and that are readily available in the USA and Canada are Airtrim and Lungplus. Both are effective at preventing bronchoconstriction during exercise and reducing the amount of lung damage caused by exercising in extreme-cold temperatures. A neck warmer or “buff” is also effective, but actually has higher mechanical resistance to breathing (Ainegren et. al, accepted for publication) and easily wets out, rendering it difficult to breathe through after a few minutes. Lungplus has the advantage of being dishwasher friendly and small whilst Airtrim has an advantage in airflow capabilities, facial coverage and being crash-safe. Ultimately in training, you should use what you are comfortable with and what gives you the best feeling. In competition, you will very rarely see a mask being used, and until recently we haven’t had definitive data as to why.
Preliminary results from research I was involved in this past year at the Swedish Winter Sports Research Centre suggest that during sprint-type competition scenarios the Airtrim mask may affect ventilation enough to cause a decrease in performance in people without asthma. How much? On average about two to three seconds during a typical sprint distance of three and a half to four minutes. At the elite level, this is significant and could cost you around 15 places when you line up in Ruka at the World Cup as the only person with a mask on. However, it is worthwhile to note that individual results did vary across the sample group significantly, so some non-asthmatics will experience a performance benefit from mask use in short, maximum intensity competitions such as sprint races. Another study (Frischut et. al 2020) found no negative effects of the Lungplus HME on performance, however, it is worthwhile to note that the protocols and durations of studies differed by about 25 minutes and self-paced vs. fixed-speed. Our recommendation is therefore that you should test and decide what works for you until further data becomes available for generalized advice. During training, a mask may raise your heart rate and feelings of perceived exertion slightly, but not enough to take you from L1 to L2, and in return, they may actually improve lung function and certainly protect the airways a little from the cold.
So what does this mean? Based on the available literature, if you are asthmatic you probably should be training with an HME below circa 20°F to prevent a decrease in ventilation. That part is quite simple, where it gets more complex and where many questions remain unanswered is what non-asthmatics and young adolescents should do to prevent lung damage and/or improve performance and comfort in cold weather. Our preliminary results show a tendency towards a lesser negative effect of performance the smaller you are, with the regression line crossing the axis at circa 110lbs, which means that children and smaller adults are less likely to experience performance loss compared to a larger adult when wearing a HME. About half of our sample used HME at least occasionally in temperatures below 12°F to prevent potential future decreases in lung function and the Airtrim Mask with Sport filter was the most commonly used amongst Swedish Elite Ski Gymnasium athletes.
