Muscle contractions use more ATP than another other process. The ATP supply has to be constant due to the fact that the muscle cell only contains enough ATP for a contraction to last three seconds.
Muscle cells are able to produce ATP through three systems:
- the aerobic system
- the anaerobic or glycogen-lactate system
- the creatine phosphate system
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The aerobic system
When the muscles are resting or only moderately active they can produce ATP via aerobic respiration. This system produces ATP at a constant rate however the contractions are quite slow because the rate depends on how fast the blood supplies oxygen and the substrates required. They’re the only system which respire fats which makes aerobic exercise a good way to lose weight.
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The anaerobic or glycogen-lactate system
As the rate of muscle contraction increases there comes a point where not enough ATP can be produced through aerobic respiration. Instead, the muscles switch to anaerobic respiration of glycogen. Due to the fact that there’s no need to wait for substances in the blood, this system is faster. However, the waste product lactate builds up and leads to muscle fatigue. It’s also limited and can create ATP for about 90 seconds of muscle contractions only. This system can be used for short distance races.
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The creatine phosphate system
When muscle contractions reach their maximum speed an even faster process is required: the creatine phosphate system. In it ATP is produced from creatine phosphate. Like glycogen, it’s also stored in the muscle cells and can create ATP very quickly. In fact, it’s actually made from ATP during the period in which the muscles are relaxed. It’s able to produce around 10 seconds of rapid contractions for little bursts of intense activity, like a sprint.
Hopefully this will have helped with your As and A level biology revision.