Muscle Respiration

Muscle Respiration

For muscles to contract, energy is required.

This energy can only be provided by the breakdown of a chemical called Adenosine Triphosphate (ATP).

Muscle Respiration

Now see this reaction in action:

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During this reaction, energy is released and two new chemicals are formed:Adenosine Diphosphate (ADP) and phosphate (P).

There is a limited quantity of ATP in the muscle cells.

For muscle contraction to continue ATP has to be re-built from ADP and P.


This re-building of ATP is known as Muscle Respiration.

There are two pathways by which ATP can be reformed:

  • The Anaerobic Pathway
  • The Aerobic Pathway

Anaerobic is without oxygen.

This means there is no oxygen present when ATP is reformed.

There are two methods of Anaerobic Respiration:

1. The Alactic or Creatine Phosphate (CP) System.

There is another chemical present in the muscle cell called Creatine Phosphate (CP).

When there is a demand, due to muscle contraction, for ATP to be re-built CP breaks down, giving up its P to add to ADP to form ATP + C.

ADP + CP = ATP + C.

Like ADP, the cell has a limited quantity of CP in it, so this method of muscle respiration can only be used when short burst of energy are required such as in shot-putt or sprint starting.

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Because there is a limited amount of CP, if further muscle contractions are required then another method of muscle respiration is necessary.

2. The Lactic Acid System.

Present in all cells of the body is a food substance called glycogen, which is made from glucose obtained from digested food.

When glycogen breaks down in the cell it releases energy. This energy is then used to re-build ATP from ADP and P.

ADP + P + glycogen = ATP + pyruvic acid

As the lactic acid system is anaerobic, there is no oxygen present. Pyruvic acid without the presence of oxygen forms lactic acid.

It is the build up of lactic acid in the muscle that causes pain, discomfort and fatigue.

Consequently this method of muscle respiration can only be used for events lasting short periods of time form between two to two and a half minutes.

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Examples of this are the longer sprints or the final part of longer events.

For longer events the body muscles must work with oxygen present, that is, aerobically.

This pathway begins like the lactic acid system.

ADP + P + glycogen = ATP + pyruvic acid

However, because oxygen is present pyruvic acid is not converted into lactic acid but goes on to form another 34 molecules of ATP.

Muscle Respiration
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