3.1.1.6 Energy systems Typeit

At the onset of exercise, whether that be low- or high-intensity, there is a lag in  delivery to the muscle and/or inertia of the mitochondria to carry out aerobic respiration, which inhibits resynthesis of  via this pathway for the first ~2–5 minutes. This appears as the oxygen , which accrues sub-maximally during low-intensity exercise and maximally during high-intensity exercise. Either way, it must be repaid in equal quantity during the recovery process. Most of us have experienced the acute increase in ventilation that occurs as soon as we finish exercise. This is a practical example of how  (EPOC) aims to restore the oxygen deficit accumulated at the beginning of exercise.

The overarching role of EPOC is to return the body to its pre-exercise state. It does this through two components:

1. component: This is concerned with the survivalist instinct of replenishing the oxygen content of  in the blood (oxygen saturation), and the oxygen content of  (the oxygen-binding pigment in the muscle). Additionally, adenosine triphosphate (ATP) and phosphocreatine (PC) – the components of the ATP-PC system that provide the most rapid release of energy for muscle contraction – are resynthesised. This involves the reverse of the reaction which breaks down PC in the first place: this time  combines with phosphate (P) and the free energy from aerobic respiration to replenish ATP, while + P + free energy → PC. Even when fully depleted, PC stores are usually restored to 50 % complete within 30 seconds post-exercise, making an almost full recovery within ~3–4 minutes.
2.  component: The processes in this component ensure an elevated ventilation, blood circulation and body  for an extended period of time post-exercise. The elevation of these systems can last up to ~60 minutes, until the body returns to homeostasis. These processes help remove the  from the muscle and the blood which is produced as a by-product in anaerobic glycolysis. As well as being removed, lactate can also be utilised by the body as a fuel source. When lactate is transported to the liver, gluconeogenesis occurs in the liver, which converts it to for storage. This process is known as the Cori cycle, named after the two brothers who discovered it.