Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Exercise Intolerance is a term used to describe a condition where the patient is unable to do physical exercise at the level that would be expected of someone in his or her general physical condition, or experiences unusually severe post-exercise pain, fatigue, or other negative effects. Exercise intolerance is not a disease or syndrome in and of itself, but a symptom.
Since there are many possible specific reasons why exercise could be inhibited, this is a rather slippery term. For instance, the patient may experience unusual breathlessness (dyspnea), muscle pain (myalgia), or increasing muscle weakness while exercising, or may, after exercise, experience severe headache, nausea, or extreme fatigue. In most cases the specific reason that exercise is not tolerated is of considerable significance when trying to isolate the cause down to a specific disease.
Exercise intolerance is primarily found in organic brain diseases, mitochondrial disease and neuromuscular disease.
Many diseases have exercise intolerance as one of the only symptoms, as in the case of some of the less severe metabolic myopathies. Nonspecific fatigue or pain syndromes such as chronic fatigue syndrome, fibromyalgia and Overtraining Syndrome are all collections of symptoms, one of likely to be exercise intolerance.
Exercise intolerance can also be caused by specific health conditions, such as heart conditions or conditions that cause back pain. Several heart conditions, such as a cardiac arrhythmia (abnormal heart rate or rhythm) or an aortic valve insufficiency, if severe enough can cause activity problems such as shortness of breath and/or exercise intolerance. People with acute back pain from an injury or chronic back pain (e.g., from a degenerative condition) may also experience exercise limitations due to muscle spasms or limited range of spinal motion. Exercise is key for many heart and back patients, and a variety of specific exercise techniques are available for both groups. Some exercise specialists (e.g., physical therapists, athletic trainers) are trained in modifications specific to these patients.
Certain conditions in particular exist where exercise, particularly rehabilitation, may be contraindicated, including:
- decompensated heart failure
- recent MI
- hypertrophic cardiomyopathy or cardiomyopathy from recent myocarditis
- active or suspected myocarditis or pericarditis
- low left ventricular ejection fraction
- severe aortic stenosis
- unstable ischemia
- unstable arrhythmia
- irregular or resting pulse greater than 100 bpm
- resting systolic blood pressure >200 mm Hg or resting diastolic blood pressure >110 mm Hg
- severe pulmonary hypertension
- suspected or known dissecting aneurysm
- recent systemic or pulmonary embolus
- pneumothorax and haemoptysis
Other conditions may also preclude exercising under certain conditions. Passive physiotherapy can in some instances be an alternative for some patients unable to safely self-power.