Ultrarunning Magazine

Take a deep breath. The air you just inhaled took only a few seconds to travel from your nose to your lungs in a system of tubes so extensive that, if you lay them end to end, it would stretch from New York to Miami. The pair of lungs you inflated, two balloons occupying the chest, have a combined surface area the size of a tennis court, and the tiny air sacs responsible for transiting air into the blood are more numerous than people in the US and so thin that oxygen moves through them as a ghostly apparition moves through walls. Your respiratory system is the supercar you never knew you had. At rest, it’s essentially idle, operating at about 5% capacity. During exercise, however, it can rapidly shift gears and, at a moment’s notice, inflate and deflate the lungs once a second, exchanging enough air in a minute to fill a bathtub. Whatever your running ability, whether you’re back of the pack or chasing the podium, a healthy respiratory system is a wonderfully sophisticated piece of machinery that rarely limits performance and is generally overbuilt for its demands (1).

But even supercars degrade when you clock up enough miles. Once we hit middle age, wear and tear causes respiratory health to decline by 1-2% every year (2). And something about the demands athletes place on their bodies can predispose them to worse respiratory health in the long run. The prevalence of asthma and related disorders is twice as high in athletes compared to the general population, and nearly five times higher in endurance athletes – swimmers, rowers, cyclists, runners and triathletes (3). These are essential statistics that too often go unreported and ignored by people who need to know better. Could running increase your chances of developing respiratory issues?

How Does Training Affect the Respiratory System?

John Wooden was known as the “Wizard of Westwood.” The legendary UCLA basketball coach passed away in 2010 at the age of 99, leaving a coaching legacy few could rival. One of his most memorable philosophies was that training and preparation should be considered as long-term financial investments – that athletes needed to accrue “wealth” so they were ready to make big withdrawals when it came time for a major competition. Each training session was money in the bank.

I love this philosophy because it resonates from a biological perspective. Body systems don’t change perceptibly after a single training session. Only after many months or years do tiny, incremental adaptations eventually accumulate, resulting in cardiovascular and musculoskeletal systems capable of performing at a greater capacity than before. You can’t cram for an ultra – it takes time.

However, unlike other body systems that are inherently malleable, you cannot increase your lung capacity or make your lungs “stronger,” no matter how hard you train. Much like your height, your lung size is determined by the blueprint in your DNA and set in stone by the time you reach adulthood. Only the respiratory muscles (e.g., the diaphragm and abdominals) can be trained, becoming stronger and more fatigue-resistant with time. Training them increases their ability to generate force, partly explaining athletes' superior lung function scores relative to population norms (4). It’s also likely that people with better lung function are predisposed to high-level sport, bringing us back to the steadfast question of nature vs. nurture.

Endurance training is a double-edged sword, and some respiratory adaptations can leave us worse off. The airways are usually the weak link. With each breath, the airways give up heat and water so that oxygen reaches the lungs warmed and humidified. This is great for gas diffusion into the blood but dehydrates the airways, causing inflammation, airway narrowing and mucous production in susceptible people. This is known as having a “hyperresponsive airway,” and it’s more likely to happen in cold, dry conditions. Repeatedly injuring the airway smooth muscle in this way can cause the development of scar tissue, cellular remodeling and long-term damage (5).

There are many other triggers for respiratory symptoms. Airborne allergens like pollen, dust mites, mold spores, pet dander, smoke and pollution can all trigger airway inflammation. For people with pre-existing asthma, poor air quality is a real concern, and lung illnesses are far more likely to occur in places with high pollution levels and lower air quality (6).

Competing with Respiratory Problems

Russel Winwood is a 58-year-old Australian-born individual who, in 2004, was diagnosed with chronic obstructive pulmonary disease (COPD) – a progressive respiratory disease characterized by airway obstruction. But, unlike most patients with COPD who shy away from physical activity due to unpleasant breathlessness, Winwood tackled the disease head-on. Driven by a desire to improve his health and manage the challenges of his condition, he began an endurance and strength training regimen. Soon thereafter, he entered a triathlon to test his fitness. Since 2005, Winwood has become a multiple-time marathon and Ironman finisher, showcasing his resilience and ability to thrive despite living with COPD.

Of course, it has been an ongoing struggle for Winwood, who continues to accomplish these feats due to his dogged determination and thoughtful and realistic approach to training. He tailors his program to his abilities, uses physician-prescribed bronchodilators and corticosteroids and follows a healthy diet and breathing exercises. His journey is an inspiration, and he truly embodies the quote on the front page of his website (copdathlete.com): “Never let your disease define you.”

Winwood started training after his diagnosis, but many athletes develop respiratory symptoms decades into their athletic careers. In 2022, I was approached by a female ultrarunner who had developed severe respiratory symptoms during her long runs. Primarily, she had breathlessness and chest tightness, but in demanding conditions, she described how it felt like she was “breathing through a straw.” It wasn’t uncommon for her unpleasant respiratory symptoms to force her to withdraw from a race, and longer runs caused a “productive cough,” which is a polite way of saying she had a lot of phlegm. Her symptoms steadily worsened over the years and were generally worse when it was cold outside.

If any of this sounds familiar, you should first see a respiratory expert. Little therapeutic advice can be given without a clinical assessment to diagnose any issues. That’s what I recommended to the athlete. When she eventually secured an appointment, her pulmonologist performed a series of tests and determined she had exercise-induced bronchoconstriction (EIB) – a disorder with symptoms similar to asthma but generally only arising during exercise.

She was prescribed albuterol, a beta-agonist that helps the airways to relax and expand, thereby relieving much of her breathing discomfort. However, she still had lingering symptoms, especially when running in the cold, so I suggested a heat exchanger as an adjunct to the albuterol. Heat exchangers are facemasks worn during exercise that capture heat and moisture from the exhaled breath, making it available for subsequent inhalation. There’s some interesting, albeit limited, evidence for the benefits of heat exchangers (8), but it made a substantial difference to her perceptions, and that’s much of the battle. Something similar, albeit less effective, can be achieved with any face covering that traps heat and moisture: a buff is perfect for this, and it’s thin so it won’t add much resistance to breathing. With this conservative management, she’s since run dozens of races and broken several records.

These two examples should be all the evidence you need that respiratory symptoms, as long as they’re effectively managed, don’t have to derail your training and racing.

How Do the Lungs and Airways Respond to Ultrarunning?

A few years ago, a team of intrepid researchers and I ventured to Chamonix, France, to study runners at the Ultra-Trail du Mont Blanc (UTMB) – one of the world’s most grueling 100-milers. The nature of the race, which traverses the French, Swiss and Italian Alps, added logistical complexity to an already complicated study. We first had to transport our fragile measuring devices – ultrasound scanners, lung spirometers, blood sampling apparatus – from the United States to Geneva and then onto Chamonix via minibus. It then took 5 hours to transform a series of bare rooms at the National School of Mountain Sports into a sophisticated physiology laboratory.

Our data collection lasted more than a day, accommodating the first of our athletes who finished CCC in 15 hours and the last who finished UTMB in 45 hours. It was exhausting but rewarding work. The unique observation was that finishers tended to retain water in the lungs, a condition known as pulmonary edema (9). I know what you’re thinking: the lungs are for air, not water. And that’s the problem. Due to fluid in the lungs and the downstream effects, athletes’ ability to diffuse oxygen through the lungs and into the blood was diminished. Although none of the runners needed medical attention, it took some of them weeks to recover, and we don’t yet know whether repeated pulmonary edema (from periodic racing) will lead to damaged soft tissue in the lungs.

Our study at UTMB was published earlier this year and is only the most recent investigation in a discipline that began in 1981 when researchers studied finishers of the Lake Waramaug Ultramarathon in Connecticut. They, too, saw lung function decline considerably after the race, indicating airway obstruction in the marathon runners (10), probably due to airways that’d become inflamed and, therefore, narrowed. Since then, roughly a dozen papers have shown something similar in various distances and timed events: lung function generally declines by 10-15% after a race (11). Function typically recovers within a few days, but, as with pulmonary edema, we’re still exploring if there could be lingering effects.

A Note on COVID

Contrary to our hopes and expectations, COVID isn’t over. The rates of severe disease and death remain considerably higher than for other respiratory infections (e.g., the common cold and influenza), and COVID is now endemic, with rates of infection continuing to wax and wane. The good news is that the disease severity has generally declined, and we have effective vaccines that considerably reduce the risk of hospitalization. Based on the current advice, most runners can expect to return to training within 1-2 weeks of an infection (12). The process shouldn’t be rushed but guided by the severity of the infection and individual symptoms.

A small percentage of individuals may suffer long-term symptoms and even Long COVID. The CDC defines Long COVID as “a chronic condition that occurs after SARS-CoV-2 infection and is present for at least three months.” The symptoms vary wildly from person to person, with more than 200 symptoms so far linked to the disorder, mostly extreme tiredness, especially after activity, memory problems or “brain fog,” dizziness, problems with taste or smell, sleep issues, shortness of breath, persistent cough, headaches, irregular heartbeat and digestive issues.

Being young and fit is also no guarantee. Many elite distance runners have been hit hard by COVID. A recent report in the British Medical Journal highlighted the case of an elite distance runner in his late 30s who had a marked decline in performance that persisted long after he initially had COVID (13). Even at five months post-infection, his anaerobic threshold (also called the gas exchanged threshold) remained 13% lower than pre-infection levels – more than enough to put the podium beyond reach. So, even if you escape severe symptoms, the long-term effects on training and racing can be debilitating.

As is often the case, the best cure is prevention. Stay updated on your vaccines when made available to you, avoid diminishing your immune system by overtraining and be proactive about reducing your risk of contact with an infected person. All of this will be even more important in the lead-up to an important race. At that time, you should consider avoiding large gatherings, wearing a facemask and implementing other behavioral changes. After all, it’d be a shame to diligently train for an event only to be sniped by an infection at the final hour.

Actionable Takeaways

Most of us don’t think about respiratory health until it starts to wane. Modern medicine has gifted us effective medications and therapies to manage respiratory issues. Still, they’re primarily aimed at symptom relief: by the time you need them, the damage has already been done. As endurance athletes, we’re perhaps more susceptible to poor long-term respiratory health because of the strain we put on the breathing apparatus and the conditions in which we run, exposing us to additional hazards in the form of cold, dry air, pollutants and allergens. Although we’re far from having a complete picture of how the lungs and airways respond to ultrarunning, each new study adds another piece to the puzzle. Fortunately, we know enough to give actionable advice to stop your respiratory health from running away from you:

1. Monitor your breathing during exercise. Are you disproportionately breathless, given the pace? Does your chest feel tight? Are you producing a lot of phlegm? Do you cough during or after your run? Consider diarizing your experiences or using a validated respiratory survey, like the four-item Respiratory Symptoms Questionnaire (14). If you’re concerned about your respiratory health, speak to your physician.

2. Avoid exercising outdoors when it’s very cold and dry, especially if your symptoms are noticeably worse in these conditions. If you do run in the cold, consider using a face covering, e.g., a thin buff, which will trap heat and moisture, making it available for the next inhalation. If your symptoms are severe, consider a more dedicated heat-exchanger.

3. Check air quality before training outdoors, especially in cities or wildfire-prone areas. During a typical 1-hour run, you'll take 2,000 - 3,000 breaths, exposing you to high levels of particulate matter and volatile compounds. Minimize risk by wearing a mask, training indoors, or, perish the thought, rescheduling your workout.

References

1. Dempsey JA, La Gerche A, Hull JH. Is the healthy respiratory system built just right, overbuilt, or underbuilt to meet the demands imposed by exercise? J Appl Physiol Bethesda Md 1985 129: 1235–1256, 2020. doi: 10.1152/japplphysiol.00444.2020.

2. American Lung Association. Lung Capacity and Aging [Online]. 2024. https://www.lung.org/lung-health-diseases/how-lungs-work/lung-capacity-and-aging [5 Oct. 2024].

3. Rasmussen SM, Hansen ESH, Backer V. Asthma in elite athletes – do they have Type 2 or non-Type 2 disease? A new insight on the endotypes among elite athletes. Front Allergy 3: 973004, 2022. doi: 10.3389/falgy.2022.973004.

4. Williams Z, Jackson A, Ranson C, Hull J. 834 EP103 – Lung function in elite athletes: the recipe for a long life? Br J Sports Med 58: A122–A122, 2024. doi: 10.1136/bjsports-2024-IOC.218.

5. Anderson SD, Kippelen P. Airway injury as a mechanism for exercise-induced bronchoconstriction in elite athletes. J Allergy Clin Immunol 122: 225–235; quiz 236–237, 2008. doi: 10.1016/j.jaci.2008.05.001.

6. Behinaein P, Hutchings H, Knapp T, Okereke IC. The growing impact of air quality on lung-related illness: a narrative review. J Thorac Dis 15: 5055–5063, 2023. doi: 10.21037/jtd-23-544.

7. Cross-Country Runner Saved with CPR on Race Course [Online]. Run. World: 2023. https://www.runnersworld.com/news/a45615314/paramedics-save-cross-country-runner/ [12 Oct. 2024].

8. Jackson AR, Hull JH, Hopker JG, Fletcher H, Gowers W, Birring SS, Dickinson JW. The impact of a heat and moisture exchange mask on respiratory symptoms and airway response to exercise in asthma. ERJ Open Res 6: 00271–02019, 2020. doi: 10.1183/23120541.00271-2019.

9. Stewart GM, Fermoyle CC, Wheatley-Guy CM, Robach P, Tiller NB, Taylor BJ, Ziegler B, Schwartz J, Gavet A, Chabridon L, Murdock RW, Constantini K, Johnson BD. Effect of Ultramarathon Trail Running at Sea Level and Altitude on Alveolar-Capillary Function and Lung Diffusion. Med Sci Sports Exerc 56: 1759–1769, 2024. doi: 10.1249/MSS.0000000000003448.

10. Mahler DA, Loke J. Pulmonary dysfunction in ultramarathon runners. Yale J Biol Med 54: 243–248, 1981.

11. Tiller NB. Pulmonary and Respiratory Muscle Function in Response to Marathon and Ultra-Marathon Running: A Review. Sports Med Auckl NZ 49: 1031–1041, 2019. doi: 10.1007/s40279-019-01105-w.

12. Hughes DC, Orchard JW, Partridge EM, La Gerche A, Broderick C. Return to exercise post-COVID-19 infection: A pragmatic approach in mid-2022. J Sci Med Sport 25: 544–547, 2022. doi: 10.1016/j.jsams.2022.06.001.

13. Barker-Davies RM, Ladlow P, Chamley R, Nicol E, Holdsworth DA. Reduced athletic performance post-COVID-19 is associated with reduced anaerobic threshold. BMJ Case Rep 16: e250191, 2023. doi: 10.1136/bcr-2022-250191.