The ATP-PCr (Alactic) System
- ATP needs to be recycled. However rapid increase in activity means there is no Oxygen available. The body therefore relies upon an energy rich compound found in the muscles- PCr (Phosphocreatine).
- Breakdown of phosphocreatine takes place in the sarcoplasm and is facilitated by the enzyme Creatine Kinase.
- The release of Creatine Kinase is stimulated by the increase of ADP and Pi (Inorganic Phosphates).
PCr----> Creatine + Pi +Energy
Unlike ATP, the energy released from breakdown of phosphocreatine is not used for muscle contraction but instead used to recycle ATP so that it can be broken down to maintain a constant energy supply.
Energy + ADP + Pi ----------> ATP
(from PCr)
This is an endothermic reaction as energy is required for it to take place.
Coupled Reaction
Because PCr exists alongside ATP in the sarcoplasm as rapidy as energy is released from ATP during exercise it is restored through the breakdown of PCr. This occurs almost simultaneously. It takes one molecule of PCr to recycle one molecule of ATP.
Advantages of ATP-PC System to the athlete-
- Very quick at resynthesising ATP by PCr.
- PCr stored are recovered quickly- within 2-3 mins after stopping exercise
- Anaerobic process so doesnt need to wait for 3 mins or so for oxygen to be present.
- No fatiguing by-products which delays recovery
- Some athletes may try to extend the time they can used this energy system for by creatine supplementation
Drawbacks to ATP-PCr system to athlete
- Only a limited supply of PCr stored in muscle cell. Only sufficient to resynthesise ATP for 10 secs. Fatigue occurs when concentrations of PCr fall and can no longer sustain ATP resynthesis
- Resynthesis of PCr can only occur when there is sufficient oxygen available- usually resting conditions after exercise has stopped.
- Only one mole of ATP can be recycled through one mole of PCr
Practical Application of Knowledge
http://www.youtube.com/watch?v=-Gu1nr5n4HU&feature=related
Usain Bolt split time shows fatigue from ATP-PCr system
http://www.sport-fitness-advisor.com/energysystems.html
http://physiqueconsultant.com/tag/atp-pcr-system/
Further Reading