Monday, 16 July 2012

Fatigue And How The Body Recovers From Exercise


Fatigue

Depletion of energy sources

Creatine phosphate

Depletion of Creatine phosphate is found at the muscles. Creatine phosphate is synthesised in the liver and then goes to the skeletal muscles to be stored. Creathine phosphate is used to form ATP from ADP. It is also important for intense exercise for up to ten seconds like 100 metres maximum power cannot be maintained.

Muscle and liver glycogen    

Muscle and liver glycogen can occur despite that there is enough oxygen and ATP through metabolic pathways. Glycogen is a readily available source of energy under both aerobic and anaerobic conditions. When glycogen stores are depleted muscles stop contracting because the body is unable to use fat as a sole source of fuel. Fatty acids from fat stores cannot be fully oxidised to release all their energy if there is insufficient breakdown of carbohydrates at the same time.     

Effects of waste products

Blood lactate accumulation

Muscle lactate is disposed by oxidation at first then to pyruvate and then turned to carbon dioxide and water. Some blood lactate is taken in by the liver which reconstructs it to glycogen. The remaining blood lactate diffuses back into the muscle or other organs to be oxidised. This oxidation forms carbon dioxide which is later excreted by the lungs.    

Carbon dioxide

During exercise carbon dioxide increases the level of blood activity. Carbon dioxide is carried in chemical combinations in the blood. In red blood cells enzymes speed up the reaction of carbon dioxide and water to form carbonic acid. 

Increased blood acidity

When the carbonic acid breaks down it breaks down into hydrogen ions and bicarbonate ions. The hydrogen ion is responsible for the increased blood acidity.  

Neuromuscular fatigue

Depletion of acetylcholine

Acetylcholine is neurotransmitter that is released to stimulate skeletal muscles and the parasympathetic nervous system. Its effect are short because it is destroyed by acetlchilinesterase an enzyme which are realised into the sarcolemma of muscle fibres which then prevent muscle contractions in the absence of additional nervous stimulation.  

Reduced calcium-ion release

Calcium ions are realised allowing actin and myosin to couple and form actomyosin. During relaxation the calcium ions are removed and the muscle returns to its resting state. If the store of calcium ions is reduced the ability of the actin and myosin to couple is compromised which prevents continued muscle contraction.

Recovery

(EPOC) Exercise, post, oxygen, consumption

The two major components of EPOC are fast components and slow components. Fast components are the amount of oxygen required to synthesise and restore ATP and creatine phosphate. Slow components are the amount of oxygen required to remove lactic acid from the muscle cells and blood. After light exercise recovery to a resting state takes place quickly and without realising it. EPOC defines the excess oxygen uptake above the resting level in recovery  

Oxygen debt

When you have a short intense burst of exercise like sprinting you generate energy for this anaerobically or without oxygen, when you stop exercise you are still breathing heavily, this is your body taking in extra oxygen to repay the oxygen debt. The difference between the oxygen the body required and what it actually managed to take in during a sprint is called oxygen deficit. When you stop sprinting and start to recover you will actually need more oxygen to recover than your body. This is called excess post exercise oxygen consumption.

Fast components

Muscle phosphogen stores

Alatacid oxygen debt represents that portion of oxygen used to synthesise and restore ATP and creatin phosphate stores which have been almost completely exhausted during high intensity exercise. During the first three minutes of recovery EPOC restores almost 99 % of the ATP and creatine phosphate used during exercise.

Slow components

Removal of lactic acid

The slow component of EPOC is concerned with the removal of lactic acid from the muscles and the blood. This can take several hours depending on the intensity of the activity. Around half of lactic acid is removed after 15 minutes and most removed after an hour. Lactacid recovery converts most of the lactic acid to pyruvicacid which is oxidised by the kerbs cycle to create ATP  

Replenishment of myoglobin

Myoglobin is an oxygen storage protein found in muscle it forms a loose combination with oxygen while the oxygen supply is full and stores it until the demand for oxygen increases. During exercise the oxygen form myoglobin is quickly used up after exercise additional oxygen is required to pay back any oxygen that has been borrowed from myoglobin stores.

Replacement of glycogen

The replenishment of muscle and liver glycogen stores depends on the type of exercise. Short distance high intensity exercise may take two to three hours and long endurance activates may take several days. Replenishment of glycogen stores is most rapid during the first few hours after training is complete. To restore glycogen stores quicker you can accelerate this with high carbohydrates.  

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