Exercise Intolerance is a medical term used to describe a condition where the patient who is unable to do physical exercise at the level that would be expected of someone in his or her general physical condition, or who 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. Dyspnea (Latin dyspnoea, Greek dyspnoia from dyspnoos - short of breath) or shortness of breath (SOB) is perceived difficulty breathing or pain on breathing. ... Myalgia means muscle pain and is a symptom of many diseases and disorders. ... Weakness is the inability to exert force with ones muscles to the degree that would be expected given the individuals general physical condition. ... A headache is a condition of mild to severe pain in the head; sometimes upper back or neck pain may also be interpreted as a headache. ... Nausea (Greek Ναυτεία) is the sensation of unease and discomfort in the stomach with an urge to vomit. ... Fatigue is a feeling of excessive tiredness or lethargy, with a desire to rest, perhaps to sleep. ...

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 which is likely to be exercise intolerance. Chronic fatigue syndrome (CFS), also known as myalgic encephalomyelitis (ME), post-viral fatigue syndrome (PVFS) and various other names, is a disorder of the central nervous system (CNS) characterized by a number of features, the most common and notable one being severe fatigue, usually made worse by even modest exertion. ... Fibromyalgia is a debilitating chronic syndrome (constellation of signs and symptoms) characterized by diffuse pain, fatigue, and a wide range of other symptoms. ...