LACTATE SHUTTLE IN EXERCISE
Brooks, G. A. (1986). The lactate shuttle during exercise and recovery. Medicine and Science in Exercise and Sports, 18, 360-368.
More than 75% of the lactate formed during sustained, steady-state exercise is removed by oxidation during exercise. Only a minor fraction (approximately 20%) is converted to glucose. Of the lactate which appears in the blood, most will be removed and combusted by oxidative muscle-fibers in the active muscle bed and the heart.
During recovery from sustained exhausting exercise, most of the accumulated lactate will continue to be removed by direct oxidation. Practically all of the newly formed liver glucose will be released into the circulation to serve as a precursor for cardiac and skeletal muscle glycogen repletion. Liver glycogen depots will not be restored and muscle glycogen will not be completely restored until refeeding. This is because the diversion of lactate carbon to oxidation during exercise and recovery represents an irreversible loss of gluconeogenic precursor and because the processes of protein proteolysis and gluconeogenesis from amino acids are insufficient to achieve complete glycogen restitution after exhausting exercise.
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