Anaerobic energy systems (ATP-PC system, anaerobic glycolytic system).

The idea

Anaerobic systems resynthesise ATP without oxygen and are used at the onset of exercise and during high-intensity efforts. The ATP-PC (phosphocreatine) system uses creatine kinase to break down phosphocreatine, and the energy released rebuilds ATP from ADP and inorganic phosphate; it is very fast but lasts only a few seconds because phosphocreatine stores are small. The anaerobic glycolytic (lactate) system breaks down glucose or glycogen to pyruvate in the sarcoplasm, producing ATP quickly without oxygen; when pyruvate is converted to lactate, hydrogen ions accumulate and contribute to fatigue, limiting the system to roughly ten seconds to about two minutes of maximal work. Both systems have a low ATP yield compared with the aerobic system but a much faster rate, which suits sprinting, jumping and repeated high-intensity efforts.

What earns the marks

• The ATP-PC system uses phosphocreatine breakdown, catalysed by creatine kinase, to resynthesise ATP from ADP and inorganic phosphate.
• The ATP-PC system is very fast but limited by small phosphocreatine stores, lasting only a few seconds.
• The anaerobic glycolytic system breaks down glucose or glycogen to pyruvate in the sarcoplasm without oxygen.
• Pyruvate conversion to lactate is associated with hydrogen ion accumulation, which contributes to fatigue and limits duration.
• Anaerobic systems have a low ATP yield but a fast rate, suiting high-intensity, short-duration exercise.
• Anaerobic glycolysis supplies ATP for roughly ten seconds to about two minutes of maximal work.

Common mistakes and how to put them right

• Saying the ATP-PC system uses oxygen.

  Put it right: It is anaerobic and relies on phosphocreatine breakdown.

• Believing lactate itself is the sole cause of fatigue.

  Put it right: Hydrogen ion accumulation is the key contributor, and lactate is a by-product.

• Thinking anaerobic glycolysis occurs in the mitochondrion.

  Put it right: It takes place in the sarcoplasm.

• Confusing the duration of the two systems.

  Put it right: ATP-PC lasts only a few seconds, while anaerobic glycolysis extends to about two minutes.

Exam tips

• Name the enzyme creatine kinase when describing ATP-PC breakdown to show precise knowledge.
• Distinguish clearly between lactate as a by-product and hydrogen ions as the cause of fatigue.
• Link each system to a sporting example, such as a 100 m sprint for ATP-PC and a 400 m or 800 m race for anaerobic glycolysis.
• Compare anaerobic and aerobic systems in terms of rate, yield and duration to answer 'explain' questions fully.