At the 2018 Winter Olympics in Pyeongchang, something unusual caught the attention of sports journalists: elite athletes were wearing breathing devices during warm-ups and between events. When asked, many said the same thing: the devices helped protect their lungs and made breathing easier in the bitter Korean cold.
These weren't trendy accessories. They were Heat and Moisture Exchangers (HMEs), devices that capture and recycle the warmth and humidity from exhaled breath. And what those athletes knew intuitively, science has now confirmed: airway humidification isn't a luxury. It's a performance variable.
This article examines the growing body of peer-reviewed research demonstrating how dry air, whether from cold weather, climate-controlled gyms, or high-altitude training, impairs respiratory function, degrades athletic performance, and increases injury risk. More importantly, it explores the emerging science suggesting that proactive airway humidification may offer athletes a legal, drug-free edge.
The Respiratory System Under Athletic Stress
Before exploring the science of humidification, it helps to understand what happens inside your airways during intense exercise, and why they're more vulnerable than most athletes realize.
The Body's Natural Air Conditioning System
The human respiratory tract is an engineering marvel. With every breath, it performs three critical functions: warming incoming air to body temperature (37°C or 98.6°F), saturating it to 100% relative humidity, and filtering out particles and pathogens.
According to research published in Intensive and Critical Care Nursing, air entering the nose at room temperature (20°C) with 50% relative humidity carries approximately 8.7 mg of water per liter. By the time it reaches the lower airways, it must contain 44 mg of water per liter, a five-fold increase. The respiratory mucosa donates this moisture from its own tissue, drawing from a dense network of capillaries and approximately 45,000 mucus-producing glands.[1]
This system works beautifully at rest. But during intense exercise, everything changes.
When Demand Exceeds Supply
At rest, adults breathe approximately 6 to 8 liters of air per minute through the nose. During maximal exercise, ventilation rates can exceed 150 liters per minute, and much of this air enters through the mouth, bypassing the nose's superior conditioning capacity.
"Your nose does a much better job at humidifying and warming the air than your mouth. Cold air is generally drier, and your body works to humidify this. In that process, it can cause irritation to the airways, which results in bronchospasm, where those airways narrow and tighten, and you get that feeling of shortness of breath."
Dr. Aryan Shiari, Pulmonologist, Mayo Clinic Health System[2]
The research quantifies this effect. A controlled study published in Allergy, Asthma & Immunology Research (Kennedy et al., 2018) placed 17 female athletes through running trials at five different temperatures: 0°C, -5°C, -10°C, -15°C, and -20°C in an environmental chamber.[3] The results clearly demonstrated that lung function was impaired at low temperatures:
- Forced expiratory volume (FEV₁) decreased by 4 to 5% at temperatures down to -15°C, and by 7% at -20°C
- Forced expiratory flow (FEF₂₅₋₇₅) decreased by up to 11% at the coldest temperatures
- Respiratory symptoms (cough, wheeze, chest tightness) increased significantly at -15°C and below
- Recovery to baseline lung function required 15 to 20 minutes post-exercise
Notably, high-ventilation athletes, those accustomed to sustained heavy breathing during training, showed even greater dysfunction, suggesting that years of cold, dry air exposure may create cumulative airway sensitivity.
The Mucociliary System: Your Airways' First Line of Defense
Beyond the immediate effects of bronchospasm, dry air exercise creates a more insidious problem: it compromises the mucociliary clearance system, the airways' primary defense mechanism.
The tracheal and bronchial epithelium is coated by a two-layer mucus blanket. The deeper layer is fluid and watery; the superficial layer is more viscous. Millions of hair-like cilia beat continuously in the fluid layer, 12 to 15 times per second, propelling the mucus carpet upward toward the throat at approximately 1 cm per minute. This "mucociliary elevator" traps and removes inhaled particles, pathogens, and debris.
When athletes breathe large volumes of dry air, the moisture gradient between the incoming air and the mucus layer accelerates evaporation. The viscous layer thickens. In extreme cases, it can form a crust covering the airway surface. The consequences cascade:
- Thickened mucus resists ciliary propulsion, slowing clearance
- Secretion accumulation increases airway resistance
- Mucosal crusting creates susceptibility to bronchial infection
- Repeated exposure may lead to chronic airway inflammation
A landmark 2019 study published in PNAS (Kudo et al.) demonstrated that humidity directly determines innate immune competence, not merely comfort.[4] The mucociliary system requires adequate hydration to function as an effective barrier against respiratory pathogens.
Understanding VO₂ Max: The Oxygen Uptake Connection
To understand why airway health matters for athletic performance, we need to understand VO₂ max, the single most important measure of aerobic fitness.
What is VO₂ Max?
VO₂ max (maximal oxygen uptake) is the maximum rate at which your body can consume oxygen during intense exercise. Think of it as your body's "engine size," it determines how much power you can sustainably produce.
The number is expressed in milliliters of oxygen consumed per kilogram of body weight per minute (mL/kg/min). Typical values range from 30 to 45 mL/kg/min in sedentary individuals up to 85 to 90+ mL/kg/min in world-class endurance athletes like elite marathoners and cross-country skiers.
As the American Heart Association notes, VO₂ max is such a powerful predictor of health and performance that it should be considered a "clinical vital sign."[8] A 2023 meta-analysis confirmed a strong inverse relationship between VO₂ max and all-cause mortality risk: the higher your VO₂ max, the longer you're likely to live.
The Oxygen Delivery Chain
VO₂ max depends on a chain of physiological systems working together:
- Lungs: Take in oxygen from the air and transfer it to the bloodstream
- Heart: Pumps oxygen-rich blood throughout the body
- Blood vessels: Transport oxygenated blood to working muscles
- Muscles: Extract and use oxygen to produce energy for movement
Here's the critical insight: the lungs are the first link in this chain. If the airways are constricted, inflamed, or functioning inefficiently, less oxygen enters the bloodstream, and every downstream system suffers.
How Airway Dysfunction Limits Oxygen Uptake
When cold, dry air causes bronchoconstriction (airway narrowing), several things happen that directly reduce the body's ability to take in and use oxygen:
- Increased airway resistance means the respiratory muscles must work harder just to breathe, diverting energy away from locomotion
- Reduced ventilation efficiency means less fresh air reaches the alveoli (the tiny air sacs where oxygen enters the blood)
- Dynamic hyperinflation (air trapping) reduces tidal volume, how much air you can move with each breath
- Less oxygen in the blood means less oxygen available for muscles to produce energy
Research confirms this connection. Studies in cold environments show reduced VO₂ and reduced time to fatigue, suggesting decreased exercise economy: athletes cannot sustain the same pace for the same energy cost. The Kennedy et al. study found that athletes required significantly greater effort to maintain the same workload in cold conditions, with heart rate paradoxically dropping while perceived exertion increased, a sign the body was shifting toward less efficient anaerobic metabolism.
Beyond Winter Sports: The Cold, Dry Air Challenge in All Outdoor Athletics
While the most dramatic research has focused on winter endurance athletes, the cold, dry air challenge extends to virtually every outdoor sport played in fall and winter conditions.
The NFL Night Game Scenario
Consider an NFL game played on a cold November night in Denver, Colorado. Kickoff temperature: 25°F (-4°C). Relative humidity: 35%. The thin mountain air at 5,280 feet elevation already contains less oxygen per breath than at sea level.
Now layer on the respiratory challenge: players are breathing heavily through their mouths, pulling in massive volumes of cold, dry air with every sprint, tackle, and play. The body's airway conditioning system, designed for moderate nasal breathing at rest, cannot keep up. Airways dry out. Smooth muscles around the bronchi constrict. Inflammation begins.
The result? Less oxygen reaches the blood. Less oxygen reaches the muscles. Players fatigue faster. Recovery between plays takes longer. Decision-making in the fourth quarter suffers.
This isn't speculation, it's physiology. The Australian Institute of Fitness notes that breathing through the nose during exercise is beneficial because the nasal passages filter, warm, and humidify the air, allowing for better oxygen exchange in the lungs.[5] When athletes must mouth-breathe during high-intensity activity, they lose this protection.
Optimal Conditions for Oxygen Absorption
The science is clear: gas exchange in the lungs, where oxygen enters the bloodstream, is most efficient when air reaching the alveoli is warm (body temperature) and fully saturated with moisture. This is called the "Isothermic Saturation Boundary," normally located about 5 cm below the windpipe.
When athletes breathe cold, dry air at high ventilation rates, the body cannot condition the air quickly enough. The Isothermic Saturation Boundary shifts deeper into the lungs, forcing the delicate alveolar tissue to do work it wasn't designed for. This triggers protective responses (bronchoconstriction, mucus production, coughing) that further impair oxygen uptake.
Conversely, when inhaled air is properly warmed and humidified before reaching the lower airways, several beneficial effects occur:
- Airways remain relaxed and open (reduced resistance to airflow)
- Mucociliary function remains intact (maintaining airway health)
- The alveolar-capillary membrane remains optimally hydrated for gas exchange
- Oxygen transfer into the blood proceeds efficiently
This is why the implications extend far beyond Nordic skiing. Any sport played in cold, dry conditions, football, soccer, rugby, field hockey, lacrosse, distance running, cycling, presents the same respiratory challenge. The athletes who can maintain optimal airway function will have a measurable advantage in oxygen delivery to working muscles.
The Performance Penalty: From Airways to Muscles
Understanding the connection between airway function and whole-body performance requires following the oxygen from the lungs to the muscles, and understanding what happens when that supply is compromised.
Reduced Oxygen Uptake and Endurance Capacity
Research from the Scandinavian Journal of Medicine & Science in Sports confirms that cold air exercise reduces maximal oxygen uptake (VO₂ max) and depresses lung function for up to 30 minutes post-exercise in healthy athletes.[6] This isn't just discomfort, it's a quantifiable reduction in aerobic capacity.
"Research shows that your muscles may be affected enough to cut your endurance capacity, measured as how long you can hold your target pace, by 30 percent. If your core temperature drops, you can tack on another 30 percent."
Dr. Stephen Cheung, Exercise Physiology Researcher, Brock University
The Cascade to Muscle Function
Here's the critical link that connects airway function to whole-body performance: muscles need oxygen to produce energy efficiently.
When muscles have adequate oxygen, they produce energy through aerobic metabolism, a highly efficient process that can sustain performance for extended periods. One molecule of glucose burned with oxygen produces 36 units of ATP (the body's energy currency).
When oxygen supply is limited, because airways are constricted and less oxygen is reaching the blood, muscles must rely more heavily on anaerobic metabolism. This process produces only 2 ATP per glucose molecule and generates lactate as a byproduct. It's fast but inefficient, and it cannot be sustained.
The result: athletes running low on oxygen burn through their glycogen (stored carbohydrate) faster, accumulate lactate sooner, and fatigue earlier. They may also feel like they're working harder for the same pace, because they are.
Accelerated Glycogen Depletion
Cold weather compounds the problem by fundamentally changing how the body metabolizes fuel. Research shows that exercising in cold conditions shifts the body away from fat oxidation and toward glycogen consumption. Shivering alone can deplete glycogen stores five to six times faster than normal.
For endurance athletes, this has direct race-day implications: hitting "the wall," the dreaded point where glycogen stores are exhausted, happens sooner in cold conditions, even when training and nutrition are optimized.
The HME Solution: Evidence from Controlled Trials
Given the clear physiological burden of dry air exercise on both respiratory function and downstream performance, researchers have investigated whether Heat and Moisture Exchangers, devices that capture exhaled warmth and humidity and return them on inhalation, can mitigate these effects.
Understanding the Measurements: What Scientists Look For
Before examining the research, it helps to understand the key measurements scientists use to assess lung function. These are obtained through a test called spirometry, where a person breathes forcefully into a measuring device:
- FVC (Forced Vital Capacity): The total amount of air you can forcefully exhale after taking the deepest breath possible. Think of it as your lungs' "tank size."
- FEV₁ (Forced Expiratory Volume in 1 second): How much air you can blow out in the first second of that forced exhale. This measures how easily air flows through your airways; if they're constricted, FEV₁ drops.
- FEF₂₅₋₇₅ (Forced Expiratory Flow at 25 to 75%): The average airflow rate during the middle portion of your exhale. This is sensitive to changes in the smaller airways and is often one of the first indicators of bronchial irritation.
When these values drop after exercise, it indicates the airways have narrowed, a condition called exercise-induced bronchoconstriction (EIB). The lower the values, the harder it is to breathe and the less efficiently oxygen can enter the body.
The Landmark Study
The most compelling research was published in 2020 in the Scandinavian Journal of Medicine & Science in Sports by Frischhut, Kennedy, Niedermeier, and Faulhaber.[7] The randomized controlled trial placed 13 elite winter sport athletes (7 male, 6 female, with VO₂ max values of 52 to 62 mL/kg/min) through intense running trials at -20°C, with and without an HME device.
The results were unambiguous:
- Without HME: Mean FVC decreased 5.9% and FEV₁ decreased 4.2% at 3 minutes post-exercise
- With HME: FEV₁, FEF₂₅₋₇₅, and FEF₅₀ actually increased post-exercise compared to pre-exercise baseline
- Respiratory symptoms were significantly lower in the HME condition (p = .046)
- Significant interaction effects confirmed that the HME intervention, not other variables, drove the improvement
In plain language: athletes breathing through an HME device maintained better lung function after intense cold-air exercise than they had before starting, while athletes without protection experienced significant decline.
Connecting Respiratory Benefits to Whole-Body Performance
The Frischhut study focused on respiratory outcomes, but the implications for overall performance follow directly from the oxygen delivery chain discussed earlier:
- Better lung function → More oxygen enters the bloodstream
- More blood oxygen → Better oxygen delivery to working muscles
- Better muscle oxygenation → More efficient aerobic energy production
- Efficient energy production → Preserved glycogen stores, delayed fatigue
- Delayed fatigue → Sustained pace, better performance
By protecting the respiratory system, the first link in the chain, HME technology preserves the entire downstream cascade that determines athletic performance.
Current Recommendations and Gaps in the Market
Medical and sport science authorities have begun to recognize the importance of airway protection during exercise:
- Mayo Clinic Health System recommends breathing through the nose and wearing a ski mask or scarf over the nose and mouth during cold weather exercise, noting these items can trap some of the heat and moisture from your breath
- The American Lung Association advises that your nose warms and humidifies incoming air more effectively than the mouth does, and recommends face coverings that retain heat and moisture[9]
- The International Olympic Committee has issued consensus statements on thermoregulatory challenges for high-level athletes, acknowledging the respiratory burden of extreme environments
- Researchers recommend not exercising outdoors when temperatures drop below -15°C, or to cover one's mouth as a protective measure
Yet as the Frontiers in Sports and Active Living review (2020) noted, there is a lack of knowledge at present about the extent of positive and negative effects of HME use, precisely with respect to their capacity to heat and humidify inhaled air, the resistance they pose to breathing, and the effects they have on athletes' ventilation, energy cost, and performance.[10]
In other words: the science supports airway protection, the recommendations exist, but the solutions available to athletes remain limited. Scarves and ski masks provide passive thermal retention but lack the engineered moisture-exchange properties of medical-grade HMEs. And medical HMEs, designed for clinical ventilation, are neither practical nor designed for athletic use.
Implications for Athletes and the Sports Market
The convergence of respiratory physiology research and athletic performance science points toward a clear opportunity: purpose-built airway humidification technology designed for athletic use.
The athlete populations who would benefit most include:
- Winter sports athletes (Nordic skiers, biathletes, ice hockey, snowboarding, speed skating)
- Cold-weather field sport athletes (football, soccer, rugby, lacrosse, field hockey)
- Endurance athletes training through fall and winter months (runners, triathletes, cyclists)
- Altitude training athletes exposed to cold, dry mountain air
- Frequent-traveling competitors experiencing cabin air dehydration before events
- Athletes with exercise-induced bronchoconstriction (EIB), estimated at 90% of asthmatics and elevated among elite athletes
Conclusion: From Lab to Field
The science is increasingly clear: airway humidification during exercise is not a comfort measure, it's a physiological factor that directly impacts respiratory function, oxygen uptake, muscle performance, and athletic results.
The chain of evidence is now well established:
- Cold, dry air causes airway dehydration and bronchoconstriction
- Bronchoconstriction reduces lung function and oxygen uptake
- Reduced oxygen uptake forces muscles into less efficient metabolism
- Less efficient metabolism accelerates fatigue and degrades performance
- HME devices support airway function, and potentially preserve the entire downstream cascade
Elite athletes at the 2018 Pyeongchang Olympics weren't following a trend, they were following the evidence. And that evidence has only grown stronger in the years since.
References
- Jackson C. Humidification in the upper respiratory tract: a physiological overview. Intensive and Critical Care Nursing. 1996;12(1):27-32. View on PubMed ↩
- Shiari A, quoted in "Is the extreme cold bad for your lungs?" Mayo Clinic News Network. View source ↩
- Kennedy MD, Faulhaber M. Respiratory function and symptoms post cold air exercise in female high and low ventilation sport athletes. Allergy, Asthma & Immunology Research. 2018;10(1):43-51. View on PubMed ↩
- Kudo E, Song E, Yockey LJ, et al. Low ambient humidity impairs barrier function and innate resistance against influenza infection. Proceedings of the National Academy of Sciences. 2019;116(22):10905-10910. View on PubMed ↩
- Respiratory Physiology: Breathing Techniques for Performance. Australian Institute of Fitness. View source ↩
- Kennedy MD, Lenz E, Niedermeier M, Faulhaber M. Are respiratory responses to cold air exercise different in females compared to males? Implications for exercise in cold air environments. International Journal of Environmental Research and Public Health. 2020;17(18):6662. View on PubMed ↩
- Frischhut C, Kennedy MD, Niedermeier M, Faulhaber M. Effects of a heat and moisture exchanger on respiratory function and symptoms post-cold air exercise. Scandinavian Journal of Medicine & Science in Sports. 2020;30(3):591-601. View on PubMed ↩
- Ross R, Blair SN, Arena R, et al. Importance of assessing cardiorespiratory fitness in clinical practice: a case for fitness as a clinical vital sign. A scientific statement from the American Heart Association. Circulation. 2016;134(24):e653-e699. View on PubMed ↩
- Tips for Outdoor Exercise in Cold Temperatures. American Lung Association. View source ↩
- Hanstock HG, Ainegren M, Stenfors N. Exercise in sub-zero temperatures and airway health: implications for athletes with special focus on heat-and-moisture-exchanging breathing devices. Frontiers in Sports and Active Living. 2020;2:34. View on PubMed ↩
Additional sources referenced in the original research but not cited above with a specific claim: Sandsund M, Faerevik H, Reinertsen RE, Bjermer L. Effects of breathing cold and warm air on lung function and physical performance in asthmatic and nonasthmatic athletes during exercise in the cold. Ann N Y Acad Sci. 1997;813:751-756 (verified, DOI 10.1111/j.1749-6632.1997.tb51778.x). Bassett DR, Howley ET. Limiting factors for maximum oxygen uptake and determinants of endurance performance. Med Sci Sports Exerc. 2000;32(1):70-84 (verified, DOI 10.1097/00005768-200001000-00012). Keck T, Dürr J, Leiacker R, et al. Influence of passive humidification on nasal conditioning. American Journal of Rhinology. 2006;20(5):430-433 (verified, DOI 10.2500/ajr.2006.20.2919).
This article is for general educational purposes and does not constitute medical advice. Consult a healthcare provider with questions about respiratory health or exercise conditions.