Matt Brown ND2B

Task 4


The body uses food as energy as we have discussed in task 3 but when the body is low on what it needs it becomes fatigued.  Often the thing the body is low on is oxygen, this is a major factor in fatigue.

 (Wilmore and Costill, 1988) described Fatigue as a general sensation of tiredness as well as a decrease in muscular performance. Muscular fatigue occurs in athletes after a tough training session. This description is very general and does not explain what causes fatigue.

(, 2005) believe fatigue is the decreased capacity or complete inability of an organism to function normally because off excessive stimulation. This description is better then the first as it states that excessive stimulation, even lack of sleep, will cause the body to fatigue. It is the body’s way of saying it needs rest.

(Gandevia et al., 1995; Hagberg, 1981; Hawley et al., 1997) describes fatigue as the inability to continue functioning at the level of one's normal abilities. This is also very general but it is clear in what it describes.

performance may decrease for a number of reasons:(can performance improve)

  • accumulation of waste products lactic acid
  • depletion of energy stores glycogen
  • changes in physio chemical state of the muscle electrolytes
  • disturbances in the processes of muscular co-ordinbation-CNS

Neuromuscular fatigue - neural fatigue and muscular fatigue

CNS has 2 basic processes:  

  • Excitation of the necessary muscle fibers
  • Inhibition of nueral firing

Fatigue can be caused due to the inability of the CNS to activate the required muscle fibres. This occurs when the impulse doesn’t get to muscles so they don’t contract. this is because of the reduction in the release or synethesis of ACH (acetylcholine). ACH is responsible for helping the impulse jump from the nerve to the muscles (synaptic cleft).

Reasons for muscle fatigue are due to the impulse not being able to jump from the nerves to the muscles. This could occur from:

There is an increase in the amount of cholinesterase (which is responsible for destroying ACH) this means that impulse can not reach the muscle because there is nothing to help it.

There is a decrease in the amount of cholinesterase, this results in a build up of ACH. Then overloaded-muscle fibres develop a higher threshold for the ACH so the body does not produce it when it needs just a little bit. This occurs in people who do a lot of exercise like athletes. If you are an athlete your body is used to getting the ACH. the muscle gets used to having all this ACH so it doesn’t contract and needs more to fire up.

Fatigue during exercise may also be due to, less calcuim being avaliable for muscle contraction.

Result of neuromuscular fatigue is that there is a decresae in the rate at which motor units activate muscle contraction.

The effects of metabolic bi-products (lactate/carbon dioxide etc)

(Meyerhof, 1920; Hill, 1932) state it has been known that isolated muscles made to contract until fatigue accumulates lactic acid. Further, it was observed that if oxygen was present in recovery, lactic acid level declined while glycogen concentration and contractile function were restored.

The system that creates the most fatigue is the lactic acid system. This uses glucose as an energy source, this gets broken down into pyruvic acid (which gets turned into lactic acid) and hydrogen. The lactate and hydrogen ions in the muscle affect muscle contraction and cause fatigue.  It does this by interfering with the connection between actin and myosin, changes in acid base status and ca2+ ion function. Pyruvic acid can also be converted into acetyl coa. It depends if oxygen is present or not to what it gets turned into to. No oxygen presents means lactic acid, oxygen present means acetyl coa.

Join now!

(Brain Mac) states the conversion of glucose to pyruvic acid leaves a hydrogen ion which gets picked up by nicotinamide adenine dinucleotide (NAD), this becomes NADH. This drops the hydrogen off at the mitochondria to be combined with water. If there is insufficient oxygen then NADH cannot release the H+ and they build up in the cell. To prevent the rise in acidity pyruvic acid accepts H+ forming lactic acid which then dissociates into lactate and H+. Some of the lactate diffuses into the blood stream and takes some H+ with it as a way of reducing the H+ ...

This is a preview of the whole essay