Causes
Exercise intolerance is primarily found in cardiorespiratory disorders. It is also a common symptom in chronic fatigue syndrome. 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. Overtraining and (undiagnosed) anemia can also cause the intolerance. Exercise intolerance may result from mutations in mitochondrial Complex III, a complex of Co-enzyme Q10 (ubiquinol) and several proteins. Ubiquinol depletion caused by statin drug usage may also lead to muscle fatigue or exercise intolerance in some cases.
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