Altitude masks don’t simulate real altitude in the way their marketing suggests, but they may still offer some training benefits. These masks, which cover your nose and mouth and use adjustable valves to restrict airflow, are sold as a way to replicate training at elevations up to 5,500 meters. The reality is more nuanced: they primarily make your breathing muscles work harder, and whether that translates into meaningful performance gains depends on what you’re hoping to get out of them.
They Don’t Work Like Real Altitude
At genuine high altitude, the air itself contains less oxygen. Your body responds to this over days and weeks by producing more red blood cells, which improves your ability to carry oxygen. This is why elite athletes travel to places like Boulder, Colorado, or train in altitude tents for weeks at a time.
An altitude mask does something fundamentally different. It restricts the flow of air into your lungs using valves, making each breath harder to take. The oxygen concentration of the air you’re breathing is the same as everyone else at your elevation. You’re breathing the same air, just less of it per breath. This turns the normally passive act of inhaling into active muscular work, recruiting muscles in the neck and chest that don’t usually contribute much during breathing. In that sense, the mask functions more like a resistance trainer for your breathing muscles than a portable mountain.
That said, the distinction isn’t perfectly clean. A study published in Biology of Sport found that wearing a training mask during high-intensity cycling at 70% of maximum capacity did produce modest drops in blood oxygen levels. The mask creates mild hypoventilation (you’re moving less air through your lungs per minute), which can reduce the amount of oxygen that reaches your blood. So the mask does create a mild oxygen stress, just through a completely different mechanism than actual altitude.
The Case for VO2 Max and Power Gains Is Weak
The most commonly cited benefit of altitude masks is improved aerobic capacity, often measured as VO2 max. But the controlled studies tell a less exciting story. In a six-week trial published in the Journal of Sports Science and Medicine, both a mask group and a control group completed the same cycling program twice a week, with 20 minutes of high-intensity intervals per session. The mask group improved their VO2 max by 16.5% and peak power output by 13.6%. Impressive numbers, until you see that the control group, doing the exact same workouts without masks, improved by 13.5% and 9.9% respectively.
The difference between groups was not statistically significant. In other words, the training program itself drove the improvements, and the mask didn’t add a measurable extra benefit. This is a consistent finding across several studies: the exercise works, and the mask doesn’t clearly amplify the results.
Where They Might Actually Help
The most defensible benefit of altitude masks is respiratory muscle training. By forcing you to inhale against resistance, the mask strengthens the muscles involved in breathing. Research on dedicated respiratory muscle training devices (which work on a similar principle) shows meaningful gains. In one eight-week study, participants increased their inspiratory muscle strength by an average of 14 cm H₂O, with 26 out of 27 participants showing improvement. Stronger breathing muscles improve breathing efficiency and can reduce the sensation of breathlessness during hard efforts.
For most healthy athletes, breathing muscles aren’t a limiting factor in performance. But for people returning to fitness after a long break, those working on endurance in sports that involve restricted breathing patterns (like swimming or combat sports), or anyone who simply wants to feel less winded during hard efforts, this respiratory muscle training effect is real and potentially useful.
Some Blood Changes May Occur
One area where newer research complicates the “masks don’t work” narrative involves blood chemistry. A pilot study published in the Journal of Functional Morphology and Kinesiology found that five weeks of high-intensity interval training with intermittent mask use led to significant increases in red blood cell count, hemoglobin concentration, and hematocrit, with large effect sizes. The roughly 9.9% increase in red blood cell count was comparable to what’s seen with moderate-altitude training.
The proposed explanation is that the restricted ventilation creates mild oxygen deprivation at the lung level, which could trigger the body’s oxygen-sensing systems and stimulate red blood cell production over time. Researchers described this as “cumulative functional hypoxia,” where repeated bouts of restricted breathing during intense exercise accumulate enough of an oxygen stress to provoke adaptation. However, the study did not directly measure the molecular signals that would confirm this mechanism, and it was a small pilot study. These findings are intriguing but far from settled science.
The Trade-offs to Consider
Wearing a mask during training forces you to work harder just to breathe, which can reduce the intensity of the actual exercise you’re doing. If you’re gasping through a restricted valve, you may not be able to sustain the pace, power output, or volume of training that would otherwise drive adaptation. For athletes whose primary goal is getting faster or stronger, that’s a real cost. The mask may make the workout feel harder without making it more effective.
There are also comfort and safety considerations. Restricting airflow increases carbon dioxide levels in the air you rebreathe. In any device that creates a sealed space over the face, exhaled carbon dioxide can accumulate and get inhaled again. Elevated CO2 levels can cause dizziness, headaches, and respiratory distress. For healthy adults using a well-designed training mask during moderate sessions, the risk is low. But if you feel lightheaded, confused, or develop a headache during a masked workout, remove the mask immediately. These are signs of excessive carbon dioxide buildup or oxygen deprivation.
How People Use Them
In the research that does exist, the most common protocol involves wearing the mask during high-intensity interval sessions rather than all training. A typical structure from an ACE-sponsored study: two sessions per week, each lasting 30 minutes total, with a five-minute warm-up, 20 minutes of intervals (30 seconds hard, 90 seconds recovery, repeated 10 times), and a five-minute cool-down. Training intensity was adjusted over the six-week program based on perceived effort after each session.
This points to a practical approach: if you want to try a training mask, use it selectively during shorter, structured interval sessions rather than wearing it for every run or gym visit. Start at the lowest resistance setting and progress gradually. Keep your easy and recovery sessions unmasked so you can maintain the volume and intensity those workouts require.
The Bottom Line on Altitude Masks
Altitude masks are not altitude simulators. They don’t reliably produce the red blood cell adaptations that make real altitude training valuable, though emerging research suggests some hematological changes are possible with consistent use. They do strengthen breathing muscles, and they may help you become more comfortable with the sensation of breathing hard. For most recreational athletes, the same time and money spent on a well-designed training program will produce better results. If you’re drawn to the respiratory muscle training aspect specifically, a dedicated inspiratory muscle trainer may be a more targeted tool than a mask that restricts both inhalation and exhalation while potentially compromising your workout intensity.