Analyse the contribution of the ATP-PC, anaerobic glycolysis and aerobic energy systems to performance, and how they interplay across an activity.

What this dot point is asking

You must explain how each energy system resynthesises ATP, the fuel it uses, its rate and capacity, its by-products, and how the three systems interplay during real activity rather than switching on and off.

ATP is the universal energy currency

Muscle contraction is driven by adenosine triphosphate (ATP) splitting into ADP + Pi and releasing energy. The body stores only enough ATP for roughly 1-2 seconds of maximal work, so it must be continuously remade. The three energy systems differ in how fast they make ATP (rate/power) and how much they can make before fatiguing (capacity).

ATP-PC (alactic anaerobic) system

• Fuel: phosphocreatine (PC) stored in the muscle.
• Process: the enzyme creatine kinase breaks PC into creatine + Pi, and that Pi is used to rebuild ADP into ATP. No oxygen and no glucose are needed.
• Rate: the fastest of all three systems, so it powers maximal efforts.
• Duration/capacity: dominant for about 0-10 seconds because PC stores are very small; largely depleted by around 10-12 seconds of all-out work.
• By-products: heat only (no fatiguing by-product), which is why this system is called alactic.
• Recovery: PC stores replenish quickly; roughly half restored in about 30 seconds and almost fully within 2-3 minutes of rest.

Used in a 100 m sprint, a single shot put, a tennis serve or a powerlift.

Anaerobic glycolysis (lactic anaerobic) system

• Fuel: glucose and muscle/liver glycogen.
• Process: glucose is partially broken down without oxygen to resynthesise ATP.
• Rate: very fast (slower than ATP-PC, much faster than aerobic), so it dominates high-intensity efforts once PC runs low.
• Duration/capacity: the main system from about 10 seconds to roughly 1-2 minutes of maximal effort.
• By-products: hydrogen ions accumulate (often described via lactate/lactic acid). Rising H+ lowers muscle pH and is associated with the burning sensation and fatigue. Lactate itself is not the villain; it can be reused as fuel, but the acidity that accompanies its production impairs contraction.

Used in a 400 m run, a 100 m swim or repeated high-intensity efforts in team sport.

Aerobic system

• Fuel: carbohydrates (glycogen/glucose), fats (fatty acids) and, in extreme cases, protein, broken down with oxygen.
• Process: glycolysis followed by the Krebs cycle and the electron transport chain in the mitochondria.
• Rate: the slowest to produce ATP, so it cannot meet very high-intensity demands.
• Duration/capacity: virtually unlimited capacity at submaximal intensities, so it dominates any activity lasting longer than about 2-3 minutes.
• By-products: carbon dioxide and water, which are easily removed; no fatiguing acid build-up.

At low intensity, fats supply most of the energy; as intensity rises toward the LIP, the body shifts toward carbohydrate because it yields ATP faster per unit of oxygen.

Energy system interplay

The systems never work in isolation. At the start of any activity all three switch on, but the dominant contributor shifts with intensity and duration. In a soccer match, a player jogs aerobically, sprints for a 50:50 ball using ATP-PC, and sustains a long press using anaerobic glycolysis, with the aerobic system replenishing PC and clearing lactate during recovery periods. This is why interval-based team sports rely on all three.