How is ATP resynthesised by the three energy systems, and how do they interplay across the energy continuum?
Energy for exercise: ATP as the immediate energy source, the ATP-PC, glycolytic and aerobic systems (fuel, site, yield and by-products), the energy continuum, thresholds, and the factors affecting VO2 max.
A focused answer to Eduqas A-Level PE on energy for exercise: ATP and its resynthesis, the three energy systems (fuel, site, controlling enzyme, ATP yield and by-products), the energy continuum and thresholds, and the factors that affect VO2 max, with worked relative-contribution reasoning.
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What this dot point is asking
Eduqas wants you to explain how ATP is the immediate energy currency, describe how the three energy systems (ATP-PC, glycolytic and aerobic) resynthesise it (site, fuel, controlling enzyme, ATP yield and by-products), explain the energy continuum and thresholds, and outline the factors affecting VO2 max.
ATP, the energy currency
The ATP-PC system
The lactic acid (anaerobic glycolytic) system
The point at which lactate begins to accumulate faster than it can be removed is the lactate threshold (often expressed as OBLA, the onset of blood lactate accumulation, around 4 mmol per litre). Endurance training raises this threshold, so a trained athlete can work at a higher percentage of VO2 max before lactate accumulates.
The aerobic system
The energy continuum, thresholds and VO2 max
The three systems work together, not in isolation; the energy continuum describes the changing relative contribution of each as intensity and duration change. A 100 m sprint is almost wholly ATP-PC; a 1500 m race blends all three; a marathon is almost wholly aerobic. The thresholds are the points where the predominant system switches (for example the lactate threshold).
Exam-style practice questions
Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Eduqas 20194 marksA 400 m runner sprints flat out for around 50 seconds. Identify the energy system that predominates, state its fuel and its main by-product, and explain one consequence of that by-product for performance.Show worked answer →
A Component 1 applied physiology question. One mark for the system, one for the fuel, one for the by-product, one for the consequence.
The predominant system is the lactic acid (anaerobic glycolytic) system, because the effort is maximal and lasts roughly 10 to 60 seconds, beyond the 8 to 10 second capacity of the ATP-PC system. The fuel is glucose (or muscle glycogen), broken down by anaerobic glycolysis. The main by-product is lactate (and hydrogen ions, ). The accumulation of lowers muscle pH (acidosis), which inhibits enzyme activity and the contractile proteins, causing fatigue and forcing the runner to slow in the final metres.
A common dropped mark is naming "lactic acid" only as a fuel; the fuel is glucose or glycogen, and lactate is the by-product.
Eduqas 20216 marksCompare the ATP-PC system and the aerobic system in terms of their site, fuel, relative ATP yield and the type of activity each best supports. Use a named sporting example for each.Show worked answer →
A Component 1 structured comparison. Markers reward a point-by-point contrast and two named examples.
Award marks for: the ATP-PC system works in the sarcoplasm (cytoplasm) and uses phosphocreatine (PC) as its fuel, broken down by creatine kinase; it yields only 1 ATP per molecule of PC but resynthesises ATP extremely fast, so it powers very short, explosive efforts such as a shot put or a 100 m start. The aerobic system works in the mitochondria and uses glucose, glycogen and fats (with oxygen), passing through glycolysis, the Krebs cycle and the electron transport chain; it yields up to about 38 ATP per glucose molecule (commonly quoted as 36 to 38) but resynthesises ATP slowly, so it powers prolonged, lower-intensity efforts such as a marathon. The ATP-PC system is anaerobic and alactic (no fatiguing by-product) but limited by tiny PC stores; the aerobic system is the most efficient but cannot meet a sudden high power demand.
A top answer uses the figures (1 ATP versus around 38 ATP) and contrasts speed of resynthesis against total yield, with a named sport for each.
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Sources & how we know this
- Eduqas A Level Physical Education Specification — Eduqas (2016)