As a running coach, one of the most common concerns I hear—especially from newer runners—is this: “Why am I so out of breath when I run?”
If that sounds familiar, you’re not alone. Struggling to breathe while running can be frustrating, discouraging, and confusing. However, the good news is that, in most cases, it’s something we can address and improve.
There are several possible reasons you might feel breathless during a run, from pacing too fast for your current fitness level to undiagnosed asthma or simply being early in your training journey.
We’ll explore why breathing feels so hard sometimes, what could be going on under the surface, and most importantly, how to start running without feeling like you’re gasping for air.
Breathless On The Run? Here’s What Could Be Going On
Feeling out of breath while running is common—and often, it simply comes down to fitness. If you’re new to running or building back consistency, your body is still adapting. With time, patience, and regular training, your breathing should improve.
That said, shortness of breath isn’t something to ignore—especially if it happens frequently, across different runs, or despite solid fitness. In some cases, it can point to an underlying issue.
Conditions like asthma, whether undiagnosed or not well managed, can make breathing during exercise much more difficult. The good news is that with proper diagnosis and treatment, symptoms can improve significantly and risks—like asthma attacks—can be reduced.
This sensation of difficult or uncomfortable breathing during exercise is known as dyspnea. It can impact performance, increase fatigue, and make running feel discouraging—after all, it’s hard to stay motivated when every run leaves you gasping for air.
In most cases, breathlessness while running comes down to one of four things: you’re still building fitness, you’re running harder than your current ability supports, your breathing mechanics need work, or there’s an underlying respiratory condition at play.
Let’s break down each of these.
#1: Your Fitness Is Poor
One of the most common—and completely normal—reasons runners feel out of breath is simply because they are not yet in “good shape” and their bodies have not yet adapted to the rigors of running.1Romero, S. A., Minson, C. T., & Halliwill, J. R. (2017). The Cardiovascular System after Exercise. Journal of Applied Physiology, 122(4), 925–932. https://doi.org/10.1152/japplphysiol.00802.2016 If you’re newer to the sport or coming back after a break, your cardiovascular system, lungs, and respiratory muscles may not be conditioned enough to handle the sustained effort running requires.
When you’re not yet in “running shape,” your heart has to work harder to pump oxygen-rich blood to your working muscles, and your lungs have to breathe faster and deeper to keep up. This can leave you feeling breathless, even at a moderate pace.
However, the good news is that with consistent aerobic training, these systems begin to adapt. Your heart becomes more efficient at circulating blood, your breathing muscles get stronger, and your lungs learn to manage the faster rhythm of your breathing during runs.
#2: You Are Running Too Fast
Another common reason why you might feel out of breath while running is that you are running too fast for your current fitness level.
Remember, running is a total-body workout. Your heart and muscles require significantly more oxygen and nutrients than at rest, necessitating that your lungs work harder and faster to take in oxygen and exhale carbon dioxide, a metabolic waste product.2Romero, S. A., Minson, C. T., & Halliwill, J. R. (2017). The Cardiovascular System after Exercise. Journal of Applied Physiology, 122(4), 925–932. https://doi.org/10.1152/japplphysiol.00802.2016
The faster you run, the higher the energy cost per minute. This means that as exercise intensity increases, so does the rate at which your muscles and heart need oxygen.
As a result, your body tries to breathe faster and deeper, aiming to inhale as much oxygen as possible per minute.
Once you cross the anaerobic threshold, your body can no longer produce energy (ATP) fast enough through aerobic metabolic pathways (the Krebs cycle and electron transport chain).
Thus, the reliance on anaerobic glycolysis increases significantly.
Anaerobic glycolysis does not require oxygen to produce energy, and it’s not as efficient an energy-generating pathway. Additionally, anaerobic glycolysis produces end products that, in turn, cause rapid fatigue and a further increase in respiration.
When energy is produced in your muscles without oxygen, lactate and hydrogen ions (acid) are created. Lactate molecules can be further broken down to produce usable energy, but hydrogen ions accumulate, creating an acidic environment in your muscles and lowering pH in both your muscles and blood.
This creates the dreaded burning sensation you have probably experienced in your legs when running fast, and the resulting fatigue that makes your legs feel heavy and leaden.
There are various means to buffer this acid and attenuate metabolic acidosis, but this can increase the carbon dioxide level in your blood.
The body can only safely operate within a finite concentration of carbon dioxide because excessive amounts of this compound are toxic. Fortunately, we have a built-in mechanism to rid the body of excess carbon dioxide—exhalation.
Therefore, you will start breathing harder and faster as you rely more and more on glycolysis to expel the excess carbon dioxide that begins accumulating in the body. This, in turn, will further contribute to you feeling out of breath while running.
Slowing down and maintaining a pace below your anaerobic threshold will help prevent this sharp increase in ventilation needs.
#3: You Have Asthma
If you’ve been running for quite some time but still have trouble breathing while running, you might have undiagnosed or poorly-managed asthma.
Asthma is a chronic lung disease that causes inflammation in the airways.
Some runners have chronic asthma that can be problematic during most activities of daily living, but it’s also common to have exercise-induced asthma, wherein your asthma symptoms are triggered by physical activity and exacerbated by activities such as running.3Mayo Clinic. (2022, December 7). Exercise-induced asthma – Symptoms and causes. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/exercise-induced-asthma/symptoms-causes/syc-20372300
Untreated or poorly managed asthma can increase the risk of experiencing an asthma attack, an acute and potentially serious fit of asthma symptoms that can make getting an adequate amount of oxygen extremely difficult, even at rest.
Rescue inhalers are designed to help rapidly open up the airways and reduce inflammation, allowing you to breathe more easily.
The American Lung Association recommends that people with exercise-induced bronchoconstriction (EIB, or exercise-induced asthma) try a couple of things to reduce how much their asthma symptoms affect their ability to exercise.4Association, A. L. (n.d.). Feeling Out of Breath after a Run? It might be EIB. Www.lung.org. https://www.lung.org/blog/out-of-breath-run-eib
For starters, warming up with some gentle cardio and stretching will gradually increase your heart and breathing rates, so it isn’t such a shock to your system when you start moving at a more vigorous pace. A 5 to 10-minute warm-up is recommended.
This might include brisk walking, gradually increasing the pace, gentle cycling on a stationary bike, marching in place, or other light aerobic activities.
Dynamic stretches such as walking lunges and skipping can then get your muscles and joints moving and continue to prime your cardiovascular and respiratory systems for the workout ahead.
Discussing the best medication management plan with your healthcare provider and pre-medicating before your workout can make it easier to breathe during exercise and reduce the severity of asthmatic symptoms.
It’s also helpful to pay attention to your specific triggers aside from exercise in general. For example, is it harder to breathe when running in cold weather or in extremely dry air? Is your asthma worsened by seasonal allergies when pollen counts are high?
Keeping a log of triggers for your EIB can help you determine the best time of day to run and/or ways to modify your workout to reduce the incidence of breathing difficulties.
For example, if cold, dry air makes it especially hard to breathe while running, consider wearing a buff or a face mask to help warm and humidify the air.
Try to breathe through your nose, as nasal breathing during running warms and moisturizes the air before it reaches your lungs, thereby reducing the irritation of cold, dry air that would otherwise reach your airways.
#4: Other Medical Reasons
According to research, exercise-induced bronchoconstriction (EIB), as discussed, and exercise-induced laryngeal obstruction are two common causes of dyspnea in athletes. Both essentially involve some degree of airway dysfunction. 5Smoliga, J. M., Mohseni, Z. S., Berwager, J. D., & Hegedus, E. J. (2016). Common causes of dyspnoea in athletes: a practical approach for diagnosis and management. Breathe, 12(2), e22–e37. https://doi.org/10.1183/20734735.006416
However, there are also other potential health reasons why you may experience shortness of breath during exercise. For example, iron deficiency and anemia both affect your body’s ability to transport enough oxygen to your working muscles.
This can cause you to breathe more rapidly while still feeling insufficiently satisfied in meeting your oxygen needs.
If you’re new to running and struggling to breathe, be patient with your body as it adapts, take walking breaks as necessary, and slow down. Your fitness will improve, but you must slow down to allow your body to take in enough oxygen per minute.
If you have concerns about asthma or other medical issues, be sure to speak with your healthcare provider.
If you would like to learn about the differences between mouth and nose breathing while running to see what you should be doing, check out this next guide:
Age can also be an issue. I’m 64 and have been running consistently over the past couple of years, and compared to my younger days, I require up to a whole mile of walk/run warm-up done after active stretching, before my breathing and legs feel ready to begin my actual run. Once I’m very warmed up, I can maintain a good pace and steady breathing, plus be able to turn it on for the last mile or two picking up the pace and my heart rate. Maybe my low resting heart rate (45) has something to do with it also because once I’m in my groove, my steady running heart rate is 145-160.