Energy for muscle contraction

ATP has to be continually generated so exercise can continue - this happens in 3 main ways:

1. Aerobic respiration 

• most ATP is generated via oxidative phosphorylation in the cell's mitochondria
• It only works where there is oxygen so it is good for long periods of low intensity exercise e.g a long walk 

2. Anaerobic respiration

• ATP is made rapidly by glycolysis. The end product of glycolysis is pyruvate, which is converted to lactate by lactate fermentation.
• Lactate can quickly build up in the muscles and cause muscle fatigue. 
• it is good for short periods of hard exercise, e.g a 400m sprint

3. ATP-phosphocreatine(PCr) system-

• ATP is made by phosphorylating ADP (taken from PCr). PCr is stored in cells and the ATP-PCr system generates ATP very quickly. It runs out very quickly, is anaerobic and alactic.