Lactate at the cellular level. Usually not oxygen shortage per se, but acute energy requirements is a key determinant of lactate levels. a Under stable conditions, glucose is converted to pyruvate, generating 2 ATP, and pyruvate is then subsequently fully oxidized to CO2 generating ~36 ATP. b Under stress, glycolysis can increase by a factor 100 to 1,000, provided that glucose is present and pyruvate is converted to lactate. Irrespective of optimal mitochondrial function and oxygenation, such a rate of pyruvate production will saturate the mitochondrial tricarboxylic acid cycle and oxidative phosphorylation (OxPhos). c During recovery, lactate is converted back to pyruvate and fully oxidized.