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Mechanisms of Fatigue

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BTEC National Diploma in Sport and Exercise Science Unit 4 Exercise Physiology Assignment 3 Metabolic by- products Lactic acid is the main by- product of anaerobic glycolysis. Blood always contains a small amount of lactic acid. However this increases with high intensity exercise. The pH level of blood decreases. This may affect the muscle and neural functions. The mechanisms of fatigue are: * Onset of Blood Lactate Accumulation (OBLA) OBLA is also known as the anaerobic threshold. Which is the point at which lactate begins to accumulate in the muscles. OBLA is considered to occur at approximately 85% of maximum heart rate. * Excess Post Exercise Oxygen Consumption (EPOC) Oxygen debt is sometimes known as excess post exercise oxygen consumption (EPOC). EPOC refers to the amount of oxygen consumed after exercise in excess of a pre- exercise baseline level. EPOC occurs when a person is exercising at a high intensity where oxygen cannot be supplied to the muscle fibres. ...read more.


The higher the fitness level of the person the higher the oxygen debt this is because training increases the PCr content within the muscle cells. However the recovery time is reduced as they have superior methods of oxygen delivery, such as increased capillarisation which will increase the rate of ATP production from the aerobic energy system. * Lactacid Oxygen Debt The Lactacid oxygen debt takes much longer to complete depending on the intensity of the exercise. The process involves oxygen, which is required to break down lactic acid into pyruvate. This can then enter the aerobic system and eventually be broken down into carbon dioxide and water. Lactic Acid + Oxygen= Pyruvate Neuromuscular Fatigue Neuromuscular fatigue means that muscles are either not able to receive signals from the central nervous system that stimulate muscle contraction or that the muscle tissue is unable to function properly. This is because exercise can eventually interfere with calcium release, which is required for muscle contraction. ...read more.


Not enough ATP us produced aerobically so glycolysis takes over as the predominate method of ATP supply with its rapid depletion of muscle glycogen and production of lactic acid as a by- product. Oxymyoglobin stores supply a limited amount of oxygen to muscle to generate ATP anaerobically. Eventually, ATP production via the anaerobic system will by used up and exercise must. During the exercise period an oxygen deficit is created. This is because the muscle requirement for oxygen is larger than the oxygen supply. The oxygen deficit for a specific exercise regime is calculated as the difference between the oxygen required and oxygen actually consumed. \ The breakdown of glucose or glycogen produces lactate and hydrogen ions - for each lactate molecule, one hydrogen ion is formed. The presence of hydrogen ions makes the muscle acidic that will eventually halt muscle function. As hydrogen ion concentrations increase the blood and muscle become acidic. This acidic environment will slow down enzyme activity and ultimately the breakdown of glucose itself. Acidic muscles will aggravate associated nerve endings causing pain and increase irritation of the central nervous system. ...read more.

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