Energy Systems

ATP

Adenosine triphosphate, the immediate usable energy source for cells.

ATP resynthesis

The process of producing ATP again after it has been broken down.

ADP

Adenosine diphosphate, a product of ATP breakdown.

Phosphocreatine (PC)

A high-energy compound stored in muscle that helps rapidly resynthesise ATP.

ATP-PC system

Anaerobic system that rapidly resynthesises ATP using phosphocreatine.

Anaerobic

Without oxygen.

Aerobic

With oxygen.

Glycolysis

Breakdown of glucose.

Glycogen

Stored form of carbohydrate.

Lactate

A substance produced during anaerobic metabolism that can be transported and used as a fuel.

Mitochondria

Cell structures where much aerobic ATP production occurs.

Krebs cycle

A stage of aerobic energy production.

Electron transport chain

Stage of aerobic respiration where most ATP is produced.

Oxygen deficit

The gap between the oxygen required at the start of exercise and the oxygen actually being taken up.

EPOC

Excess Post-Exercise Oxygen Consumption, the elevated oxygen consumption after exercise.

Steady state

A state where oxygen uptake and energy demand are relatively stable during moderate exercise.

VO₂ max

Maximum rate of oxygen uptake and use.

Anaerobic glycolytic system

Also known as the lactate system, it rapidly produces ATP from glucose or glycogen without requiring oxygen.

Aerobic system

Energy system that produces ATP using oxygen and is dominant during longer-duration exercise.

Phosphocreatine recovery

The process in which phosphocreatine stores are replenished primarily through aerobic metabolism after exercise.

Muscle glycogen

Stored form of carbohydrate primarily found in muscles and liver.

Carbohydrate loading

A nutritional strategy to increase muscle glycogen stores before prolonged endurance events.

Fatigue

A state that can occur when ATP demand exceeds ATP resynthesis, leading to decreased performance.

Energy system adaptations

Improvements in the body's ability to produce and use energy as a result of training.

Lactate production

The process by which lactate is generated during anaerobic glycolysis and its role in exercise.

Hydrogen ion accumulation

The increase of hydrogen ions in the muscles that can lead to increased acidity and fatigue during high-intensity exercise.