In a recent post, I argued that it was still important to take measures to keep our community safe from COVID including getting boosters and masking while indoors. At this point, I hope that it is just common sense that N95 or equivalent masks basically work, especially if most people in a room are wearing them and they are properly fitted. I’ve done some prior posts on the science behind this. In this post I’m going to go in a different direction and look at the exercise physiology involved with masking and how it may benefit you (aside from keeping you well).
If you have ever trained with a mask on, you know that airflow is restricted. If you’ve been in one of our padwork classes, you have probably been sucking air at the end of a round, dying to rip off your mask and take in the sweet oxygen from the surrounding room. If that’s the case, your mask is working to protect you and others around you, and you may be getting an unintentional benefit to your training.
N95 masks and their clones are surprisingly similar to altitude simulation masks (ASM), which started becoming popular a few years ago with athletes seeking to enhance their conditioning. The original idea was that such masks would simulate the conditions faced by athletes who train at higher altitudes, such as the US Olympic Training Center (USOTC) in Colorado. At such altitudes, there is less oxygen, and as such, the body has to work harder to do the same amount of exercise.
In particular, your body needs to produce more of a hormone called erythropoietin (EPO). This hormone helps your body to produce red blood cells. Since red blood cells carry oxygen molecules, having more means being more efficient in your exercise, right? The usual endpoint measure of this is VO2max which is measured in milliters per kilogram of body weight per minute. The higher this is the better since it means you’ve got more red blood cells doing their thing. EPO may also improve insulin resistance in skeletal muscle as shown by mice models and thereby increase fat oxidation (fat burning) in muscles. There’s even been some debate about EPO leading to muscle hypertrophy (growth), but the jury still seems to be out on that one. So given all this, why wouldn’t you want to train with an ASM? After all, it’s supposed to simulate a trip to the Rockies.
First of all, we need a reality check on the differences between being at higher altitude and training with an ASM. The fundamental one is that athletes who are at the USOTC live there and stay at altitude even when they aren’t training. They aren’t “taking off” the altitude when they are uncomfortable. Work by Sinex & Chapman (2015) has shown that even for those using more sophisticated means of hypoxic (low oxygen) training, a minimum of 12 h/day for 21 days is needed for an effect. How big an effect will probably depend on what sport you play. Most users of ASMs will likely use them for training sessions and then remove them during break as they step outside to breath and recover. If this is what’s happening, then you’re definitely not even in the ballpark of the time needed for high altitude type physiology gains. This means that you won’t see an improved VO2max from the mask use compared to someone who does the same training without the mask. You are also unlikely to see any EPO improvements.
This is backed up by a study by Porcari et al (2016) which found that after a twice a week, 6-week high intensity cycle ergometer training program, VO2max was not improved in the masked group compared to the control group (no masks). In this study subjects’ workouts were comprised of 5 minutes warmup, 20 minutes of intervals, and 5 minutes of cool down. Masks were progressively adjusted as time went on to simulate higher and higher altitudes starting at about 914 m above sea level at week 1 (Chamonix, France ~90% O2 at sea level), to 3658 m above sea level at weeks 5 and 6 (La Paz, Boliva ~ 63.2% O2 at sea level).
But Porcari et al did find something curious – both the ventilatory threshhold (VT) and the power output (PO) at the ventilatory threshhold were significantly improved in the masked group. What’s the ventilatory threshhold? If you’ve ever run to the point where you feel you can’t get enough air in, you’ve reached it. In short, the VT is the point at which you need more oxygen than you are able to take in, regardless of how quickly you breath. So an improvement in VT means that you can go longer OR with more effort before you reach this point. Their interpretation of this finding is that wearing such masks may improve the conditioning of your respiratory muscles. This is no small thing, especially in sports which demand sudden high efforts. But how do surgical or N95 masks compare?
Part of this answer comes from Poon et al’s work in 2021 which looked at how surgical masks affect an exerciser’s rate of perceived exertion (RPE) as well as some physiological variables. This measure, selected by the subject to rate an activity, ranges from 6-20 and was originally supposed to be a quick guesstimate of heart rate, since heart rate measures intensity. For example, an RPE of 6 should equate approximately to 60 beats per minute which is close to a typical adult’s resting heart rate. Thirteen colleged aged volunteers were randomized into doing graded exercise tests on treadmills either with or without masks. The randomization, in this case, worked such that some volunteers went with the mask first, and then later repeated the test without, and vice verca. While physiological parameters with the masks were no different than without, the RPE was found to be significantly higher with the mask on. In another larger study by Lin et al (2022) using a similar crossover design with 34 volunteers, use of surgical masks did significantly affect subjects’ work rate, heart rate, oxygen consumption, and other indices implying that it may not just be a feeling that you’re struggling, but something real.
How do we square these reduced performance parameters with the improved VT from Porcari’s work? In the case of Lin et al, it was a test/retest use of a mask, whereas Porcari’s work involved a 6 week training protocol, and the measurements were made at the start of the study and then at its conclusion.
So what about the N95 masks? How do they stack up in all this? They are better at keeping out germs than the ASMs (which actually have vents), and for all intents and purposes seem to work as respiratory resistance in that they do reduce oxygen flow similarly to the surgical masks and the ASMs. I’ve written extensively about how they compare to other masks (as have many authors), and N95s are definitely a step up in restricting air flow. Whereas Lin et al showed that surgical masks may reduce the volume of O2 (VO2/kg) by 5-8% dependent on the phase of the exercise, work by Tong et al (2015) indicated that VO2 may be reduced by about 14% on average. This is similar to training in Boulder, CO which has only about 86% of the oxygen at sea level. Now Tong et al’s work was on pregnant healthcare workers, but it tracks pretty closely with what we know about filtration efficiency as N95s are known to be about twice as good as surgical masks.
Now to be clear – there’s a lot of “it stands to reason” going on in this discussion. In science, if we want to truly test something, then we have to specifically test it. But often before one gets to that point, one has to have a pretty good idea of if it’s even worth looking at. If you have a lab and a K5 Cosmed O2 sensor, have at it! Test those N95s or KN95s and see if regular exercise with such a mask improves your subject’s ventilatory threshold. In the meantime, we have a pretty good educated guess that it does, presuming that your subjects are working hard enough, long enough, and with enough frequency. So if you are wearing that mask while you train with us, despite the discomfort, you may be not just keeping your classmates well, but also improving your performance. Neat, right?
All the best,
Sifu Tim Niiler