Exercise intolerance is a condition of inability or decreased ability to perform physical exercise at the normally expected level or duration for people of that age, size, sex, and muscle mass. It also includes experiences of unusually severe post-exercise pain, fatigue, nausea, vomiting or other negative effects. Exercise intolerance is not a disease or syndrome in and of itself, but can result from various disorders. 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. Dysfunctions involving the pulmonary, cardiovascular or neuromuscular systems have been frequently found to be associated with exercise intolerance, with behavioural causes also playing a part. Signs and symptoms Exercise in this context means physical activity, not specifically exercise in a fitness program. For example, a person with exercise intolerance after a heart attack may not be able to sustain the amount of physical activity needed to walk through a grocery store or to cook a meal. In a person who does not tolerate exercise well, physical activity may cause unusual breathlessness (dyspnea), muscle pain (myalgia), tachypnoea (abnormally rapid breathing), tachycardia (having a faster heart rate than normal) or increasing muscle weakness; or exercise might result in severe headache, nausea, dizziness, occasional muscle cramps or extreme fatigue, which would make it intolerable. The three most common reasons people give for being unable to tolerate a normal amount of exercise or physical activity are: breathlessness – commonly seen in people with lung diseases, and heart disease. fatigue – when it appears early in an exercise test, it is usually due to deconditioning (either through a sedentary lifestyle or while convalescing from a long illness), but it can indicate heart, lung or neuromuscular diseases. pain – can be caused by a variety of medical conditions, such as arthritis, claudication, peripheral vascular disease, or angina. Chronic pain that makes a person unwilling to undertake a physical activity is not, by itself, a form of exercise intolerance. Causes Neurological disorders Multiple sclerosis Respiratory disorders Cystic fibrosis: CF can cause skeletal muscle atrophy, however more commonly it can cause exercise intolerance. The exercise intolerance is associated with reduced pulmonary function that is the origin of CF. Bronchiectasis Chronic fatigue syndrome (CFS) Post-exertional malaise is one of the main symptoms of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). PEM can be described as "a delayed and significant exacerbation