Mitochondrial myopathy has a variety of manifestations and can be induced by exercise or persist. Exercise intolerance is common and is manifested by easy fatigue even for daily activities, such as climbing a flight of stairs, which can be continued after rest, but can be followed by fatigue again. The phenomenon of excessive easy fatigue is not proportional to muscle weakness, and muscle atrophy is not obvious. Patients complain of heaviness and muscle discomfort in the lower extremities after exertion, but do not experience muscle spasm, stiffness or diaphoresis similar to glycogen accumulation disease. It is easily misdiagnosed as chronic fatigue syndrome or fibromyalgia. The majority of patients with mitochondrial myopathy have mutations in the cytochrome b gene of complex 3 or the ND gene of complex 1, and muscle biopsies are positive for RRF and COX. mtDNA rearrangements or tRNA point mutations are the most common manifestations of mitochondrial myopathy, while mutations in the gene encoding the complex subunit protein are only partially manifested as mitochondrial myopathy. Some patients with mutations in nuclear genes may exhibit mitochondrial myopathy and RRF, such as autosomal dominant CPEO or mtDNA depletion syndrome. Mutations in the nuclear gene encoding subunits 1 and 2 of the complex tend to manifest clinically as leigh, but usually not as mitochondrial myopathy or RRF, whereas patients with mutations in the SURF1 gene, which causes defects in complex 4, show widespread COX deficiency in myofibers and no RRF. Some patients with mtDNA may have exercise-induced headache, vomiting, exercise-induced deafness, or even encephalopathy. Symptoms of exercise intolerance are seen in certain conditions that are more dependent on mitochondrial energy metabolic function, such as starvation, infection. Blood ck may be normal, or mildly elevated, not exceeding 5-fold. In severe cases, respiratory muscles may be involved, mostly to a lesser degree. Blood lactate sensitivity is low, specificity is high, but there are false positives. Urinary organic acid analysis may show elevated ethylmalonic acid, 3-methylglutenedioic acid and ferredoxic acid.