The VCE Phys Ed Network

Ok heres my question guys; How is it possible to use the lactic acid system repeatidly during continuous exercise (which is not possible for the ATP-PC system) without recovery?

Good question. Although both systems are replenished through the aerobic pathway, the ATP-PC system cannot be adequately replenished when exercise intensity is high as oxygen is in higher demand for glucose oxidation, removal of H+ and lactate oxidation. Glycolysis occurs in the cytosol (not the mitochondria) and whether the pyruvic acid that results is oxidised or converted into lactic acid depends on oxygen availability. The first part of both anaerobic glycolysis and aerobic glycolysis is the same. So glucose levels in the muscles don't have a great effect on which energy system is used. The reason why an energy system (in the case of aerobic or lactic acid systems) is used more or less is because an exercise intensity cannot be sustained due to fatiguing by-products such as hydrogen ions. Given that background, the lactic acid system can be used repeatedly, but its contribution diminishes (and also exercise intensity) in each reoccurring effort because it takes a long time for hydrogen ions to be removed. The ATP-PC system once used initially only contributes about 1% to energy output because it needs a passive recovery to be properly replenished. Conversely, lactic acid is best broken down actively during exercise. Does that make sense?

In summary, the Lactic acid system can be used repeatidly because it can be replenished through various levels of intensity, whilst the ATP-PC system requires the body to reduce its level of intensity so that it can fully replenish the PC within the body?