Exercise Intolerance

by | Jul 18, 2023 | Blog, General Wellness

You used to be an active person. Going for a walk or an easy yoga workout wasn’t a big deal. But suddenly, any time you try to exercise, you feel exhausted and out of breath. Not even two minutes on your bike or even walking your dog feels exhausting. You are not out of shape — but something is going on.

You may have exercise intolerance. Exercise intolerance can significantly decrease your ability to exercise or even perform daily activities that used to feel normal. You may develop exercise intolerance for a number of reasons, including mast cell activation, long hauler syndrome, diabetes, chronic fatigue syndrome, and heart failure. 

In this article, I want to go over what exercise intolerance is. You will understand the signs and symptoms, major causes, and diagnosis of exercise intolerance. I will also offer some recommendations to improve your symptoms of exercise intolerance and regain your normal lifestyle.

What Is Exercise Intolerance

Exercise (EI) refers to a decreased ability or inability to exercise and perform physical activities typical for your age and size. If you have exercise intolerance, it may mean that you are suddenly not able to exercise as vigorously as before. You may get fatigued or out of breath very quickly. Even if you were moderately or seriously active before, you might start to experience difficulty performing light exercise and even everyday activities. 

You may develop exercise intolerance due to a variety of health reasons. I will go over some of the potential underlying issues behind exercise intolerance later in this article. However, exercise intolerance may also be a primary symptom of diastolic heart failure (1). This means that you have to take it seriously and rule out heart issues as a potential cause.

Exercise Intolerance vs Lack of Fitness

Don’t confuse exercise intolerance with a lack of fitness. If you haven’t exercised in a while due to injuries, illness, surgery, or any life circumstances, it is understandable that exercise and even everyday tasks feel more difficult at first. If you’ve never been active and are perhaps overweight or have health issues, it is normal that it will be challenging at first. 

You have to slowly build up strength and endurance to be able to exercise longer or perform more difficult movements. This is not exercise intolerance though. If you have exercise intolerance, it means that physical activities will suddenly become increasingly difficult without any apparent reason and even if you were in shape before.

Exercise Intolerance vs PEM

Post-exertional malaise (PEM) is similar to exercise intolerance. However, it’s not the same. It may also make physical activity difficult or prevent you from exercising. However, PEM causes a delayed reaction, while symptoms of exercise intolerance show up as soon as you begin exercising. 

If you have PEM, your symptoms (often pre-existing medical symptoms) tend to get worse after 12 to 48 hours post-exercise. These symptoms may last for several days or even a few weeks. Dealing with PEM can be difficult because you may not know that you’ve done too much until a day or two later (2).

Signs and Symptoms of Exercise Intolerance

Signs and symptoms of exercise intolerance show up soon after you start your physical activity. They may include feeling:

  • Exhausted and fatigued
  • Weak
  • Out of breath
  • In pain
  • Nauseous or vomiting
  • Heaviness in the limbs
  • Muscle soreness
  • Irregular heartbeat

When to Seek Emergency Help

Since exercise intolerance may be a symptom of heart failure and may also be confused with some serious issues, it’s important to know when to seek emergency help. Call 911 if you notice the following symptoms:

  • Chest pain, pressure, or squeezing
  • Difficulty breathing
  • Pain in arms, jaw, or neck
  • Blue or white lips
  • Feeling faint or fainting
  • Loss of consciousness

Causes of Exercise Intolerance

There may be a number of underlying causes behind your exercise intolerance. Let’s look at some potential issues:

Respiratory Issues

Certain respiratory conditions, including asthma, lung cancer, and chronic obstructive pulmonary disease (COPD), can lead to a decreased ability to breathe and make it more challenging to get enough oxygen. This may cause you to feel lightheaded, short of breath, or dizzy when you work out. It may also cause asthma symptoms, coughing, wheezing, or tightness in your chest (3).

Long Hauler Syndrome

Exercise intolerance is another potential symptom of long hauler syndrome, also known as long COVID, and other post-viral syndromes. Long hauler syndrome may cause fatigue, body aches, lingering respiratory and lung problems, immune health issues, and other problems that can trigger exercise intolerance. According to a 2021 review published in the Journal Brasiliano de Pneumenologia, COVID-19 may cause chronic symptoms for weeks and months in a large percentage of patients (4). This may not only lead to physical deconditioning and fatigue but also cardiocirculatory issues and pulmonary problems, which may play a role in exercise intolerance post-COVID.

Mast Cell Activation Syndrome

Mast cell activation syndrome (MCAS) may also lead to exercise intolerance. Since MCAS may play a role in many long hauler syndrome, it may be another reason behind exercise intolerance post-COVID (5). According to a 2017 review published in Exercise and Sports Sciences Review, histamine may play a role in exercise (6). Exercise, particularly cardiovascular activity, can increase histamine levels. This may cause an increase in allergy symptoms and inflammation. Exercise also puts stress on the body which may activate your mast cells and cause histamine release. While at a normal level, this may actually help your recovery process, if you have mast cell issues or histamine intolerance, it may lead to exercise intolerance or histamine-related symptoms (7, 8).


Postural orthostatic tachycardia syndrome (POTS) is a type of dysautonomia that affects your heart rate, breathing, and blood pressure. If you have POTS, when you stand up the blood flow to your heart will decrease. To correct this, your body will increase your heart rate by 30 beats per minute or more. This can lead to lightheadedness, dizziness, fainting, and other symptoms that usually resolve when sitting or laying down. Since symptoms come up when standing up or moving into an upright position, this can clearly cause poor exercise tolerance (9).

Chronic Fatigue Syndrome

Chronic fatigue syndrome (CFS), also known as myalgic encephalitis (ME) is characterized by an ongoing lack of energy and extreme fatigue despite rest and sleeping. Having CFS can make exercise and even daily activities increasingly difficult. Research has shown that experiencing viral infection, or significant stress are among the main reasons one may develop CFS. This suggests that post-viral syndrome and/or post-viral mast cell activation issues may play a role in CFS-related exercise intolerance and symptoms (10, 11).


Insulin resistance, pre-diabetes, and type 2 diabetes may all play a role in exercise intolerance. These conditions affect how your body uses glucose for energy. According to a 2015 study published in the Journal of Applied Physiology, people with type 2 diabetes may experience exercise intolerance even if they don’t have other issues that can affect exercise abilities, such as heart disease (12). In diabetes-related exercise intolerance, your circulation may be affected due to the blood vessels not working properly. Since exercise may help to improve diabetes symptoms, experiencing diabetes-related exercise intolerance may hinder treatment.

Metabolic Myopathies

Metabolic myopathies are caused by genetic conditions that affect how your body uses energy. If you have metabolic myopathy, exercise may cause muscles to break down, causing kidney issues. This is called rhabdomyolysis (13). Metabolic myopathies may cause exercise intolerance, heart problems, muscle cramps, and rust-colored urine.

Motor Neuron Diseases

Motor neuron diseases are a group of health conditions that develop when your nerves and brain are unable to communicate with your muscles properly, leading to issues with movement. This can lead to increased fatigue, weaker muscles, and difficulty or an inability to move (14). Amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS) are some examples of this disease that, in early stages, cause muscle cramps, spasms, muscle weakening, fatigue, and unexplained weight loss.

Heart Failure

Finally, exercise intolerance may be a sign of chronic heart failure. Most heart conditions can impact your heart’s ability to pump blood which can lead to difficulty exercising. However, in heart failure, your heart is no longer able to pump blood around as it should. According to a 2019 review published in the Journal of American College of Cardiology, exercise intolerance in heart failure patients may worsen the outcomes and increase the risk of cardiac arrest (15).

Exercise Intolerance and Mitochondrial Dysfunction

The mitochondria is the powerhouse of your health. Without mitochondrial health, your cells and body can’t function normally. This also means not having enough energy. Research has shown that there may be a connection between exercise intolerance and mitochondrial dysfunction. 

According to a 2012 study published in Neuromuscular Disorders, using coenzyme Q10 (CoQ10) may help to improve mitochondrial function and exercise intolerance (16). According to a 2017 study published in Open Heart, exercise intolerance may be an issue in people with metabolic dysfunction, heart failure, or diabetes (17). The patient group with mitochondrial issues was a younger subset with exercise intolerance. As with everything, mitochondrial dysfunction is on a spectrum. It may affect people at various levels. 

Moreover, COVID-19 may also impact mitochondrial function. According to a 2022 research published in Biomedicines, mitochondrial dysfunction may characterize long COVID (18). Thus, it may be important to look for underlying long hauler issues if you have exercise intolerance and address these issues. You may learn more about long hauler syndrome here and here.

Diagnosis of Exercise Intolerance

Diagnosis of exercise intolerance may involve a number of tests, including cardiopulmonary exercise testing (CPET), also referred to as VO2 (maximal oxygen consumption) testing to check aerobic capacity, cardiac stress tests with an electrocardiogram (ECG) to check heart test, a nuclear test for a more advanced cardiac test, imaging (ultrasound, PET scan, SPECT scan, myocardial perfusion imaging, etc.), as needed, and other tests. You may also need some blood or other tests to check for underlying reasons behind exercise intolerance, such as MCAS, post-viral syndrome, POTS, or diabetes.

Recommendations for Exercise Intolerance

Your treatment and recovery from exercise intolerance may greatly depend on your symptoms and the underlying issues behind your problems. It’s critical that you work with a knowledgeable doctor that can help to address any underlying health issues and offer appropriate strategies to overcome this.

As a general recommendation, it’s important that you understand your individual limits, triggers, and symptoms. Keeping a diary of your activities and symptoms can be very helpful for your healthcare professionals and yourself. 

If you have exercise intolerance, you may benefit from adapting your physical activities or trying new exercise options. If you have trouble with daily tasks, you may try to prepare food and cook while sitting down, using a stool in the shower, or using other assistive equipment as needed. However, if you are ready to start exercising, you may try low-impact, light activities, such as yoga, light swimming, easy walks, stretching, or Pilates. You may also work with a physical therapist or occupational therapist to guide you.

Dietary and Lifestyle Modifications

If your underlying issues include mast cell activation syndrome, histamine intolerance, post-viral syndrome, chronic fatigue syndrome, diabetes, or other chronic issues, you may greatly benefit from dietary and lifestyle modifications:

  • Remove inflammatory foods from your diet, including refined sugar, refined oil, artificial ingredients, junk food, and overly processed food. Focus on anti-inflammatory, nutrient-dense foods, such as greens, vegetables, fruits, herbs, spices, sprouts, nuts, seeds, pasture-raised poultry and eggs, grass-fed meat, and wild-caught fish. If you have MCAS or histamine intolerance, you may benefit from a low-histamine diet. 
  • Reduce your stress levels and learn to manage stress better. Try meditation, mindfulness, breathwork, guided relaxation, visualization, and journaling. Spend time in nature. Increase joy in your life.
  • Improve your sleep. Avoid electronics, stress, and heavy food before bedtime. Choose relaxing activities, such as journaling, reading, taking a bath, or listening to music. Aim for 7 to 9 hours of sleep a night.
  • Reduce exposure to environmental toxins. Choose organic and natural cleaning, body, and beauty products instead of conventional ones. Reduce the use of plastic. Reduce mold exposure. Use an indoor HEPA air filtration system and drink purified water.
  • You may also benefit from specific vitamins or herbal supplements depending on your underlying condition. I recommend working with a functional medicine doctor to get personalized recommendations.
  • Address underlying mitochondrial dysfunction and improve mitochondrial function with amenable to nutrient therapy, such as with B vitamins and CoQ10. If you have long hauler syndrome, work with a practitioner to reduce your symptoms.  I recommend working with a functional medicine doctor to get personalized recommendations.

Always listen to your body and how you feel. Take your time and be patient with yourself. As for help from professionals, family, and friends, as needed. You are not alone.

Next Steps

If you are experiencing symptoms of exercise intolerance or underlying related health issues, I recommend that you speak with your doctors first for more personalized health information and support. I invite you to schedule a consultation with me here to see if you can benefit from the strategies listed in this article. 

If you are dealing with any chronic health issues, for advice on how to improve your nutrition and health, I welcome you to start a functional medicine consultation with me for further personalized guidance. You may book your consultation here

Check out my Histamine Intolerance Course here. Learn on your own time, from anywhere. Get an inside look at the most helpful functional medicine tests for pinpointing imbalances, ways to identify and manage the most common (and sometimes surprising) mast cell triggers, and learn what to eat, what to avoid, and why.

Learn more about working with Dr. Gannage