Energy systems — AQA A-Level Physical Education

Energy systems are the metabolic pathways the body uses to resynthesise ATP for muscle contraction: the ATP-PC system (immediate, 0-10 seconds), the anaerobic glycolytic system (short-term, 10 seconds-2 minutes), and the aerobic system (long-term, 2 minutes+). Understanding their intensity, duration, fuel sources, and by-products is essential for explaining fatigue, recovery, and training adaptations in AQA A-Level PE.

The energy systems topic covers how the body resynthesises ATP (adenosine triphosphate) to provide energy for muscle contraction. It examines three systems: the ATP-PC system (immediate), the anaerobic glycolytic system (short-term), and the aerobic system (long-term). Each system differs in fuel source, duration, intensity, ATP yield, and by-products, and they interact during physical activity.

This topic is fundamental to understanding fatigue, recovery, and training adaptations in A-Level PE. It links to other areas such as muscle contraction, sports performance, and training programmes. Exam questions often require application to sporting examples, analysis of data, and evaluation of energy system contribution.

• →ATP is the only usable form of energy for muscle contraction; it is broken down into ADP + Pi, releasing energy, and must be resynthesised continuously.
• →The ATP-PC system uses phosphocreatine to rapidly resynthesise ATP anaerobically for up to 10 seconds, producing creatine and phosphate as by-products.
• →The anaerobic glycolytic system breaks down glucose to pyruvate, producing 2 ATP per glucose and lactic acid as a by-product, lasting up to 2 minutes.
• →The aerobic system uses oxygen to break down glucose, fats, or proteins, producing large amounts of ATP (up to 38 per glucose) with carbon dioxide and water as by-products.
• →The interplay of energy systems means all three contribute to ATP resynthesis at any time, but the dominant system depends on exercise intensity and duration.

• 💡Always use specific sporting examples to illustrate energy system use. For example, a 100m sprint (ATP-PC), a 400m race (glycolytic), and a marathon (aerobic).
• 💡When explaining fatigue, link the by-products to their effects: lactic acid lowers pH, inhibiting enzymes; PC depletion reduces ATP resynthesis; glycogen depletion causes hypoglycaemia.
• 💡Use correct terminology: 'resynthesis' not 'production' of ATP; 'anaerobic' not 'without oxygen'; 'predominant' not 'only' energy system.

• Students often think the ATP-PC system produces lactic acid. Correction: The ATP-PC system produces creatine and inorganic phosphate, not lactic acid. Lactic acid is a by-product of the anaerobic glycolytic system.
• Students believe that only one energy system is used at a time. Correction: All three systems contribute simultaneously, but one is predominant depending on intensity and duration. For example, the aerobic system contributes even during short sprints.
• Students confuse the order of energy system recruitment. Correction: The ATP-PC system is used first for explosive efforts, followed by the anaerobic glycolytic system, then the aerobic system as duration increases.

1. 1Day 1-2: Create a detailed comparison table of the three energy systems including fuel, duration, intensity, ATP yield, by-products, and sporting examples.
2. 2Day 3-4: Learn the stages of aerobic respiration (glycolysis, Krebs cycle, electron transport chain) and the ATP yield at each stage.
3. 3Day 5-6: Practice applying energy systems to different sporting activities, explaining the interplay and predominant system.
4. 4Day 7-8: Complete past paper questions on energy systems, focusing on 6-mark structured questions and data analysis.
5. 5Day 9-10: Review examiner reports and mark schemes to understand common pitfalls and refine exam technique.

• 📋Short answer questions (2-4 marks) asking for definitions, by-products, or duration of specific energy systems. Advice: Be precise with terminology and use correct units.
• 📋Structured 6-mark questions requiring explanation of energy system interaction during a specific sport. Advice: Use a clear structure: introduce the systems, explain the predominant system at each stage, and conclude with interplay.
• 📋Data analysis questions presenting graphs of ATP resynthesis or lactic acid concentration. Advice: Identify the dominant system from the data and explain the trends using physiological knowledge.
• 📋Evaluation questions (9-15 marks) on training programmes to improve specific energy systems. Advice: Link training methods (e.g., interval training, continuous training) to energy system adaptations and justify choices.