It is because individuals with mitochondrial disease are unable to extract and fully use oxygen, which results in a limited ability to generate energy for even normal activities. These people are not always weak or tired.They do harness some adequate amount of energy for periods of time, but it is generally for smaller duration.
So, they experience fatigue and exercise intolerance more easily. Both of them dont remain limited to large muscles, but they also affect small group of muscles as well.The people get muscle cramps and tremors. They are not even able to write as well. Too much writing leads to fatigue in them. If they exaggerate their exercise routine, they experience muscle spasm, respiratory muscle fatigue in chest wall and diaphragm.
So, this was the reason why these two symptoms are common in people with mitochondrial disease.
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Why are fatigue and “exercise intolerance” common symptoms of mitochondrial diseases?