5105SPOSCI: Physiological responses to exercise training
90TITLE: Cardio-metabolic changes in response to exercise training.
Module: 5105SPOSCI: Physiological responses to exercise training
The three main energy systems in the body used during exercise are ATP-PCr system, Glycolytic system and Aerobic system.
ATP-PCr is the system that is active only active up to first 15 seconds of exercise regardless of intensity and that is when potential power output rate is the biggest. This system is considered anaerobic, as it does not need oxygen to resynthesize. It uses creatine kinase enzyme to control the breakdown of phosphocreatine (PCr). It is most useful when doing short-term, an intensive exercise that needs a large amount of energy to be produced. It is the fastest system to resynthesize ATP (Robergs & Roberts 1997). If exercise carries on, the body would have to rely on remaining energy system as this one switches off.
Glycolytic system or lactate system do not need oxygen either, it relies on carbohydrate breakdown, which it takes either from blood glucose or muscle glycogen broken down into glucose through glycogenolysis. The product of glucose breakdown is pyruvate, which then is converted into either lactate or acetyl-CoA. Oxygen demand determines what pyruvate would be converted into however it is not required for the process itself. If there is enough oxygen, then pyruvate is being converted into acetyl-CoA and enters mitochondria to get oxidised and produce more ATP (Robergs & Roberts 1997). This process is called Krebs cycle which is linked to the last system. Alternatively, if oxygen demand is higher than the supply then pyruvate is being converted into lactate which enters the bloodstream and is cleared by the liver. Eventually, it might get to the point where production of lactate is quicker than its clearance which causes in lactate threshold when lactic acid starts to store in the bloodstream. As a result of this acidity of the blood obstruct the use of fatty acids as fuel increasing body’s reliance on CHO and glycolysis. After a while, carbohydrate stores are running out causing the muscle to fatigue.
The last system is an aerobic system which generates the most ATP. It uses Krebs cycle, blood glucose, glycogen and fat as fuel (Karp 2009). Ability to use fat as fuel is a key component of this system as our bodies have an unlimited capacity of storing fat which provides more energy per gram than protein or carbohydrate. It is much slower than another system because of its complexity and because it relies on oxygen supply, but it provides energy for an extended period of time. On top of that aerobic system provides ATP used by the body to for example control body temperature or repair muscle tissue.
The difference between relative and absolute exercise intensity is that absolute is a general measurement of intensity and it doesn’t take personal fitness level into consideration. It mostly uses METs to calculate how hard...