Metabolic myopathies include inherited disorders of muscle fat, carbohydrate, and mitochondrial muscle metabolism.

The major energy sources for muscle contraction are glycogen, glucose and fatty acids, whose metabolic pathways converge as acetyl-CoA for final intramitochondrial oxidation through the Krebs cycle and the respiratory chain. Defects of substrate utilization in muscle cause two main clinical presentations: (1) Acute, recurrent, reversible muscle dysfunction, manifesting as exercise intolerance, myalgia with or without painful cramps (contractures), often culminating in muscle breakdown and myoglobinuria; or (2) Fixed, often progressive weakness, sometimes simulating dystrophic or neurogenic processes.

Glycolytic defects refer to disorders that interfere with the breakdown of glycogen or glucose; Lipid disorders refer to defects in the breakdown of long chain fatty acid; and mitochondrial disorders to defects that impair both carbohydrate and lipid metabolism.