What is exercise intolerance?

woman suffering from exercise intolerance
(Image credit: Getty Images)

Ever felt out of breath and tired while pushing through an intense workout? These are signs that the body is working hard to pump oxygen and nutrients to your cells to produce the energy needed for strenuous movement. Exercise intolerance, however, involves extreme fatigue and shortness of breath that is not typical for your age and can occur even during lighter activities. If you have exercise intolerance, you struggle to build stamina, unlike someone who is simply out of shape.

Exercise intolerance can affect your quality of life, but there are ways to alleviate symptoms depending on the underlying cause. Exercise intolerance is associated with long Covid or post-Covid syndrome, so increasing numbers of people are experiencing these symptoms.

Exercise intolerance is still relatively unknown. We’ll cover all you need to know about the signs of exercise intolerance, the causes, and how to treat it. We’ve also asked the experts to delve into the science behind why you might experience these symptoms. 

What is exercise intolerance?

So what is exercise intolerance? “Exercise intolerance is the inability to exercise and engage in physical activity that would be typical for the individual's age,” explains physician Hallie Zwibel, D.O. and Director of the Center for Sports Medicine at the New York Institute of Technology. “It is different from someone being ‘out of shape’ due to not exercising regularly. Individuals with exercise intolerance cannot build the necessary stamina with exercise. Exercising can cause more discomfort to people with this condition.”

You may notice a significant change in your exercise tolerance, such as decreased stamina following a period of severe illness. 

Dumbbells, mat, water, on the floor in the bedroom preparing for home sports

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Exercise intolerance: Symptoms

Exercise intolerance happens when you attempt to engage in activity, but your body struggles to keep up with the demands. The symptoms can be varied but often consist of: shortness of breath, a faster heart rate, heaviness or fatigue in the legs, generalized fatigue, and weakness,” says Dr. Benjamin Levine, Professor of Internal Medicine at UT Southwestern, and Director of Texas Health Presbyterian’s Institute for Exercise and Environmental Medicine.

The symptoms of exercise intolerance may sound familiar if you’ve ever challenged yourself during a workout. So what’s the difference? Exercise intolerance is more extreme and occurs during lighter activities or everyday tasks. You may also experience other symptoms like skin discoloration. A lack of oxyhemoglobin, a bright red substance, can make your skin appear blue or purple. Post-exercise fatigue can be debilitating if you have exercise intolerance. Some people experience delayed onset of symptoms, so it’s difficult to know if you’ve pushed yourself too hard.

man lying on the sofa

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What causes exercise intolerance?

Dr. Levine explains that the symptoms of exercise intolerance show up when there is a problem with the oxygen cascade process. The process involves oxygen entering the lungs and then diffusing into the bloodstream. The heart pumps this oxygen to the muscles, and the muscles convert it into energy. Issues at any stage in the process can result in symptoms of exercise intolerance. An underlying condition is often the cause. Here are a few common ones.

Heart problems

According to Zwibel, exercise intolerance is often a symptom of “cardiac conditions where the oxygenated blood does not reach the tissues where it is needed”. 

Exercise intolerance is the primary symptom of heart failure. With this condition, the heart struggles to fill up with blood during the relaxed stage of the heartbeat. As a result, the heart transports insufficient oxygen and nutrients to the muscles. When you exert yourself, demand outstrips supply, meaning you may experience symptoms like extreme fatigue.

Respiratory conditions

It is not only your heart but your lungs that influence your exercise performance. Both organs play an essential role in supplying your muscles with energy. “Any respiratory condition can affect the ability of the lungs to move air in and out of the body and get oxygen from the lung sacs into the blood,” explains Dr. Levine. It’s no surprise that exercise intolerance is associated with conditions like Chronic Obstructive Pulmonary Disease (COPD) and asthma.

Post-viral fatigue

Recovery from a viral infection takes time — you may experience tiredness for weeks or months afterward. “Post-viral exercise intolerance is linked with Covid-19 infection,” says Zwibel. “Even after symptoms from acute Covid-19 have resolved, exercise intolerance can persist. The mechanism for this remains unclear but may be related to lung or cardiac issues.”

Chronic fatigue syndrome

Chronic fatigue syndrome is an often overlooked condition where you experience persistent, extreme tiredness, even when you first wake up. It affects your ability to carry out everyday activities. Strenuous movement like exercise can be challenging for anyone with this condition, according to the American Myalgic Encephalomyelitis and Chronic Fatigue Syndrome Society.

Can you treat exercise intolerance?

If you are diagnosed with exercise intolerance, you may be wondering whether you can treat it. The good news is that you can make changes to alleviate the symptoms and improve the quality of your life in most scenarios.

The first step is to figure out what has changed and ask why the individual has exercise intolerance,” says Dr. Levine. “Specific problems require specific therapies. For example, if the patient has coronary artery disease, they might need a stent or bypass surgery. If they have asthma, they might need drugs to dilate the lung airways. Once the specific problem has been addressed, a dedicated and individual plan of rehabilitation and exercise training is essential to restoring normal function.”

It’s best to seek support from a health professional who can give you tailored advice depending on your circumstances. Don’t forget to listen to your body — you’ll want to recognize when you’ve reached your limit. You can nip symptoms in the bud if you slow down when you first start to experience symptoms of fatigue.

Exercise can be a concern if you have exercise intolerance. A health professional can advise on whether exercise would be beneficial for you. Adaptations like performing shorter, lighter workouts under supervision can give you peace of mind. 

Louise Bond

Louise Bond is a UK-based writer specializing in health and wellbeing. She has over eight years of experience in management within health and care and brings this passion and expertise to her writing. Louise has been published in The Guardian, Planet Mindful and Psychreg among others. She is at her happiest when she is out in nature, whether that’s on an invigorating hike or pottering in the garden.