What Is Exercise Intolerance?

Exercise intolerance (EI) is the reduced capacity or inability of someone’s body to perform physical activities typical for their age. People with exercise intolerance often experience debilitating fatigue when they engage in moderate-to-vigorous physical activity, but EI can also prevent people from doing light exercise and everyday activities. Although various medical conditions can cause exercise intolerance, it is the primary symptom of diastolic heart failure.

This article discusses the signs, symptoms, and causes of exercise intolerance. It also covers how the inability to engage in physical activity due to exercise intolerance is diagnosed and treated.

Signs and Symptoms

Post-exertional malaise (PEM) and severe exhaustion are the most common symptoms of exercise intolerance. People with EI typically experience a feeling of tiredness and shortness of breath when they engage in physical exercise of any intensity, including mild exertion during everyday activities.

In those who experience disproportionate fatigue to the energy exerted during physical activity, exercise triggers what scientists call post-exertional exacerbation of fatigue. This term refers to people with exercise intolerance experiencing a "crash" in their energy levels after engaging in physical activity.

Below are some typical signs and symptoms of exercise intolerance:

• Extreme fatigue
• Tiredness
• Exhaustion
• Sluggishness
• Chest pain (angina)
• Nausea, vomiting
• Heaviness in the limbs
• Muscle soreness
• Shortness of breath (dyspnea)
  
• Irregular heartbeat (cardiac arrhythmia)

Exercise intolerance is among the most common clinical symptoms experienced by patients with atrial fibrillation (AFib or AF).

Causes

Left-sided heart failure is a leading cause of exercise intolerance. However, any medical condition that prevents oxygen-rich blood from being delivered to working muscles during physical activity (like mitochondiral diseases or metabolic disorders) can cause exercise intolerance.

For example, respiratory conditions such as chronic obstructive pulmonary disease (COPD), asthma, emphysema, and other chronic lung diseases that reduce someone's ability to take deep breaths significantly reduce the amount of oxygen available to fuel muscle contractions.

People with chronic fatigue syndrome (ME/CFS) are prone to exercise intolerance. This condition is also called systemic exertion intolerance disease (SEID). As the name suggests, chronic fatigue and "exertion intolerance" make it extremely challenging for people with ME/CFS or SEID to perform strenuous activities. Even mild exertion levels can make symptoms worse.

Although researchers aren't completely sure why ME/CFS and SEID cause severe exercise intolerance, a 2019 Norwegian study found that chronic fatigue syndrome is associated with abnormal blood lactate accumulation during physical activity, significantly reducing exercise tolerance.

The SARS-CoV-2 (COVID-19) virus can also cause exercise intolerance. An October 2022 systematic review and meta-analysis found that among those with long COVID symptoms, exercise capacity was significantly reduced more than three months after SARS-CoV-2 infection.

Diagnosis

Cardiopulmonary exercise testing (CPET), also known as VO2 (maximal oxygen consumption) testing, is a highly effective way to assess aerobic capacity and to measure how someone's body responds to physical activity at varying intensities.

CPET is used to diagnose exercise intolerance. In addition to quantifying someone's exercise tolerance, non-invasive cardiopulmonary exercise testing can identify which of multiple medical conditions are causing exercise intolerance alone or in combination.

Cardiac stress tests are a common in-office diagnostic tool that uses an electrocardiogram (ECG) to assess how the heart responds to physical activity. These cardiac exercise tests are non-invasive and don't require any injections, but they don't provide a window into the inner workings of the heart.

A nuclear stress test is more advanced than a cardiac stress test. It lets your healthcare provider see what's happening inside your heart during exercise using different imaging technologies (e.g., PET scan, SPECT scan, myocardial perfusion imaging). They inject trace amounts of radioactive material that the machines look for to see how the heart is functioning.

Other exercise tolerance tests (ETT) include:

• Exercise stress echocardiogram (ultrasound imaging)
• Dobutamine stress echocardiogram (DSE)
• Myocardial perfusion stress test
• Microvolt T-Wave alternans stress test

Treatment

Treating the root cause of exercise intolerance can create an upward spiral by making it possible for people with EI to start engaging in more physical activities and reap the health benefits of exercise. Because so many different things can cause exercise intolerance, it's important to work with a healthcare provider to get and accurate diagnosis and come up with a personalized treatment plan. This might include supervised exercise sessions. the goal is to work with a provider to come up with attainable goals specific to your needs.

Summary

Exercise intolerance is the reduced capacity to engage in physical activity experienced by people with exercise intolerance can be caused by any medical condition that prevents working muscles from getting the energy they require to exercise.

Heart problems are the most common cause of exercise intolerance, but any medical condition that prevents oxygen-rich blood from getting to the muscles that drive physical activity can cause EI. Lung issues, chronic fatigue, and long COVID can all cause exercise intolerance. Extreme tiredness, breathlessness, and irregular heartbeats are common symptoms. Many different exercise tolerance tests are used to diagnose exercise intolerance, but cardiopulmonary exercise testing is considered by many to be the gold standard.

A Word From Verywell

Before you start beating yourself up or blaming your inability to exercise on a "lack of willpower," talk to a healthcare provider about the debilitating symptoms you experience during or after physical activity. Once you've treated the issue that makes exercise so unbearable, daily physical activity can be you feel better, not something that makes you feel like you've been put through the wringer.