What is exercise intolerance called?: A Guide to Understanding This Symptom

September 29, 2025 •

5 min read

According to the Institute of Medicine, exercise intolerance is a central characteristic of systemic exertion intolerance disease (SEID), formerly known as chronic fatigue syndrome. So, what is exercise intolerance called? The answer depends on the underlying health condition causing the symptom.

Quick Summary

This condition is a complex symptom, not a disease, that can be a hallmark of various medical issues, including Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), sometimes referred to as Systemic Exertion Intolerance Disease (SEID). It also frequently points to problems with the heart, lungs, or energy metabolism.

Key Points

Symptom, Not Disease: Exercise intolerance is a symptom of an underlying medical issue, not a diagnosis in itself.
Key Terminology: It can be a defining feature of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), also called Systemic Exertion Intolerance Disease (SEID).
Underlying Causes: This condition can be caused by heart, lung, metabolic, mitochondrial, or other health problems.
Distinct from Deconditioning: Unlike being out of shape, exercise intolerance involves a severe, disproportionate, and debilitating reaction to physical activity.
Pacing Over Pushing: For many with this symptom, especially those with ME/CFS, pacing activity levels is safer and more effective than trying to push through the discomfort.
Specialized Diagnosis: Proper diagnosis relies on specialized tests like Cardiopulmonary Exercise Testing (CPET) to evaluate the body's response to exertion.

What Exactly is Exercise Intolerance?

Exercise intolerance describes a condition where an individual experiences unusual or disproportionate fatigue, pain, or other symptoms during or after physical activity that would normally be well-tolerated. Unlike simply being out of shape, where physical exertion leads to predictable, temporary discomfort, exercise intolerance involves a significant and often debilitating adverse reaction to minimal or mild exercise.

This is not a diagnosis in and of itself, but rather a red-flag symptom that points toward an underlying medical issue. The inability of the body's cardiovascular, respiratory, or musculoskeletal systems to meet the metabolic demands of even mild physical activity can trigger a variety of distressing symptoms.

Exercise Intolerance vs. Being Out of Shape

It is critical to distinguish between exercise intolerance and simple deconditioning or being out of shape. The key lies in the severity and nature of the body's response to physical effort.


Feature	Exercise Intolerance	Being Out of Shape
Onset	Often sudden or unexplained; may follow an illness or a change in health.	Gradual, related to a period of inactivity or sedentary lifestyle.
Symptom Severity	Disproportionately severe symptoms like extreme fatigue, pain, dizziness, or nausea.	Mild to moderate fatigue, muscle soreness, and shortness of breath that improves with training.
Recovery	Recovery is unusually long, potentially taking days or longer (post-exertional malaise).	Recovery is predictable and improves with regular exercise.
Progression	Does not improve with typical training and may worsen with exertion.	Improves steadily as fitness levels increase.

Medical Conditions Associated with Exercise Intolerance

Exercise intolerance can be a symptom of a wide range of medical conditions, and identifying the underlying cause is essential for effective treatment.

Myalgic Encephalomyelitis / Chronic Fatigue Syndrome (ME/CFS)

One of the most prominent conditions associated with exercise intolerance is Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), also known by the more descriptive term Systemic Exertion Intolerance Disease (SEID). For individuals with ME/CFS, even minimal mental or physical exertion can trigger a severe worsening of symptoms, known as post-exertional malaise (PEM), which can last for days or weeks.

Cardiovascular Causes

Exercise intolerance is a primary symptom of many heart-related problems because the cardiovascular system is central to delivering oxygen to the muscles during activity.

Heart failure: When the heart cannot pump blood efficiently, the body receives inadequate oxygen, leading to fatigue and shortness of breath with exertion.
Arrhythmias: Irregular heartbeats can disrupt blood flow, causing dizziness or palpitations during exercise.
Coronary artery disease: Blocked or narrowed arteries can prevent the heart from receiving enough oxygen during exercise, causing chest pain (angina) or shortness of breath.

Respiratory Conditions

Issues with the lungs can directly impair oxygen intake, causing exercise intolerance.

Chronic Obstructive Pulmonary Disease (COPD): This progressive lung disease limits airflow, making breathing difficult during physical activity.
Asthma: Exercise-induced asthma can cause airway narrowing, leading to wheezing, coughing, and breathlessness with exertion.
Pulmonary hypertension: High blood pressure in the arteries leading to the lungs can cause shortness of breath and fatigue with activity.

Metabolic and Mitochondrial Disorders

Mitochondria are the “powerhouses” of the cells, responsible for converting food into energy. Impairments can lead to exercise intolerance.

Mitochondrial diseases: These genetic conditions interfere with energy production within cells, resulting in muscle weakness and pain during exercise.
Iron deficiency anemia: A lack of iron can reduce the blood's oxygen-carrying capacity, hindering performance during exercise.

Other Medical Causes

Several other health issues can contribute to exercise intolerance, including:

Post-viral syndromes: Conditions like Long COVID often involve lingering fatigue and exercise intolerance, sometimes due to a combination of factors including cardiovascular and mitochondrial damage.
Postural Orthostatic Tachycardia Syndrome (POTS): This dysautonomia causes an abnormal heart rate increase when standing, leading to dizziness, lightheadedness, and exercise intolerance.
Neuromuscular diseases: Disorders like multiple sclerosis can cause muscle weakness and fatigue that interfere with exercise.

Symptoms of Exercise Intolerance

Recognizing the signs is crucial for seeking medical attention. Symptoms often occur soon after activity begins and can include:

Excessive or disproportionate fatigue
Shortness of breath (dyspnea) with minimal effort
Dizziness or lightheadedness
Rapid or irregular heartbeat (palpitations)
Muscle pain, soreness, or cramping that is unusual for the activity level
Nausea or vomiting
Pain, pressure, or tightness in the chest, neck, or jaw

How is Exercise Intolerance Diagnosed?

To find the underlying cause, a doctor will conduct a thorough physical examination and may order several tests.

Cardiopulmonary Exercise Testing (CPET): The "gold standard" for evaluating exercise tolerance. A patient walks or cycles while their heart rate, breathing, oxygen levels, and blood pressure are monitored to assess how their cardiovascular and respiratory systems respond to exertion.
Six-Minute Walk Test: A simpler test to measure how far a patient can walk in six minutes.
Cardiac Stress Test: Assesses the heart's function under stress by monitoring it during exercise.
Blood Tests: Used to check for metabolic conditions, anemia, thyroid issues, or inflammation markers.
Imaging: An ECG, echocardiogram, or other imaging can provide more detail on heart structure and function.

Management and Treatment

Managing exercise intolerance depends entirely on the underlying cause. Simply "pushing through" the symptoms is often ineffective and can be harmful, especially for those with conditions like ME/CFS where it can trigger a debilitating crash.

Address the Root Cause: Treatments for heart disease, respiratory illness, or other medical conditions are the first line of defense.
Graded Exercise Therapy (GET): Historically recommended for conditions like ME/CFS, GET is now viewed with caution and often replaced with pacing strategies due to the risk of post-exertional malaise. Pacing involves balancing rest and activity to stay within a person's energy envelope.
Supervised Exercise Programs: For appropriate cases, such as deconditioning or heart conditions, a supervised program can safely and gradually build fitness.
Lifestyle Changes: A balanced diet, adequate hydration, sufficient rest, and stress management are vital for managing symptoms.

It is essential to work closely with a healthcare provider to develop a safe and personalized plan. Seeking help from specialists, such as a cardiologist, pulmonologist, or rheumatologist, may be necessary to identify the specific cause. For those with complex conditions, joining a support group can also provide valuable insights and emotional support.

For more detailed information on specific medical conditions, always consult authoritative medical sources like the U.S. National Institutes of Health. For instance, the National Institutes of Health website offers extensive resources on ME/CFS and other health topics.

Frequently Asked Questions

Exercise intolerance is a symptom that can be a hallmark of various conditions. Most notably, it's a key feature of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), which is sometimes referred to as Systemic Exertion Intolerance Disease (SEID).

While being out of shape causes a predictable level of fatigue and recovery that improves with training, exercise intolerance involves a disproportionately severe and often debilitating adverse reaction to minimal physical activity. Recovery time is unusually long, and symptoms may not improve or can even worsen with typical exercise.

Post-exertional malaise (PEM) is a characteristic symptom of ME/CFS and is a specific form of exercise intolerance. It is the delayed and prolonged worsening of symptoms following physical, mental, or emotional exertion that would not have caused a problem before the illness.

To diagnose the underlying cause, doctors may use a variety of tests, including Cardiopulmonary Exercise Testing (CPET), which is the gold standard, as well as a Six-Minute Walk Test, cardiac stress tests, blood tests, and imaging like an echocardiogram.

While panic attacks or high anxiety can sometimes mimic symptoms of cardiopulmonary issues, anxiety alone is not typically the cause of exercise intolerance. However, the conditions can coexist. Objective testing, such as CPET, helps differentiate the root cause.

If you experience unusual or debilitating symptoms during or after physical activity, you should see a doctor. It's crucial to rule out serious underlying conditions, especially if you experience chest pain, severe shortness of breath, or dizziness.

Yes, exercise intolerance is treatable, but the treatment focuses on addressing the specific underlying cause, such as heart disease or a metabolic disorder. For some conditions, management involves pacing activities and lifestyle adjustments rather than pushing through with strenuous exercise.