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NBME 23 Answers
An 18-year-old woman comes to the physician because ...
Maximum oxygen consumption (VO2max): decreased;
Venous blood lactate: increased;
Energy production by glycolysis: increased
... pyruvate is shunted over and is used by LDH (lactate dehydrogenase) to generate lactate*.
It's hinted in the answer, but I would like to clarify: max O2 consumption is decreased because O2 is consumed in the Electron Transport Chain, which occurs in the mitochondria. With the mitochondria not working, the ETC cannot work, and thus there is less demand for Oxygen.
Apparently ragged red fibers are the result of coarse subsarcolemmal or intermyofibrillar mitochondrial accumulations.. https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/mitochondrial-myopathy